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THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute



 
 
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  #1  
Old June 3rd 09, 12:35 AM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
Andre Jute[_2_]
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Posts: 8,818
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

THE LOGIC OF TRIKES
an outsider's viewpoint
by Andre Jute

When an uncommitted cyclist comes to look at recumbents, he sees
bicycles in which everything has been sacrificed for aerodynamic
advantage. Recumbents were originally presented as solving the problem
of the bike saddle, the last pressure point (pun intended) of diamond
frame design, by getting the rider's weight off his butt and onto his
back, and by lowering the seat on the bike to make it easier for older
people and the less nimble to mount and dismount. So much for good
intentions.

TWO WHEELERS
Beyond aero advantage -- and its resultant of speed -- two-wheel
recumbents have no advantage over a well-designed bicycle of
traditional geometry, even over the standard diamond frame.

They do however have a great many disadvantages. The greatest of these
is near-invisibility to drivers, symbolized by a flag on a flexible
antenna carried on many recumbents.

And designers have now taken the designs to such extremes that, far
from solving the problems of mounting and dismounting, recumbents
require distortions to mount and dismount, and a flexible spine even
to see the road from the extreme recumbent positions.

The mainstream of recumbents are in such a mess both as design and
marketing exercises that a whole new concept of so-called Compact Long
Wheelbase Semi-Recumbent bicycles was created to solve the same old
saddle and mounting problems all over again, of which the Giant Revive
is already off the market again, the USED Scooterbike isn't doing too
well, and the Utopia Phoenix sells well enough into its upmarket niche
recently to have been further developed.

RECUMBENT TRIKES
At first recumbent trikes seem to have an advantage: the stability of
three wheels. We can dismiss the socalled delta tricycles with the
single wheel at the front: they are inherently unstable when compared
like for like (wheel size and seat height) with the socalled tadpole
tricyles which carry the single wheel at the rear. We can also dismiss
the novelty of rear wheel steering as unsolved and very likely
inherently unstable.

Unfortunately, even on three wheels, designers have again gone to the
extremes for a sporting advantage and thereby frittered away the
advantage of the topology for everyone heyond the speedfreak minority.
In particular, they have gone for small wheels and consequently were
forced to install seats a very few inches off the ground, suitable
only for the young and flexible to drop into, from which no one can
rise gracefully. They have also, to gain the least frontal area, made
trikes pretty narrow (which again forces a very low seat to avoid the
thing overturning on the least taxing corner taken at low speed), so
that the nominal advantage of static stability doesn't carry over very
far into the dynamics of the trike in motion.

Because of the way trikes sacrifice everything for aerodynamics, I
have severe doubts whether any trike on the market will be faster
around a downhill corner than a recumbent bicycle with the same
frontal area. The road holding and handling of a two-wheeler will in
all respects be superior on a dry road and on clean wet roads too,
leaving the exceptional case of slippery roads (cow dung, mud) as the
natural milieu of the recumbent trike -- and who wants his face inches
above that ****?

OTHER COMMON PROBLEMS
Common recumbent two-wheelers and trikes place the rider's feet
vulnerably out in front of the wheels; you can forget riding these
things in mixed automobile and pedestrian traffic. You can't use them
for a dash across a piece of pavement as you can an upright bike.
Given that the rider's height on them is conducive to a feeling of
insecurity in traffic, that limits their use severely. I define a
utility bicycle as one the owner rides from his door on every
occasion; a bicycle that must be carried on an automobile to where one
can ride it is a novelty item, not a useful bike.

Because standard types of recumbents carry the feet way out in front
of the front wheels, the chainlines are grossly inefficient and ugly
and expensive to maintain. That alone is enough to condemn recumbents
for any thoughtful engineer.

CAN A COMFORTABLE AND STABLE TRIKE BE BUILT?
It may be possible. Posit a 29er trike with 700 wheels and balloon
tyres to reduce the spinging excursion at the rear wheel, and thereby
reduce damping and other control requirements, some of the less
obvious ones to be discussed below. Of course it is a tadpole, with
two wheels forward which steer and one at the rear which is driven.
The bottom bracket is on the swing arm carrying the rear wheel and
rear suspension, and the arm is pivoted in front of the bottom bracket
or concentrically with it so that the chain line is straight and
without idlers when an internal gear hub is used. Practically then the
crank must be behind the front axle which is in any event desirable
from a safety and psychological viewpoint. The seat can be put at the
same height as an office chair so that anyone can sit down gracefully
on it and rise equally gracefully from it.

At this point the recumbent faithful will start screeching
hysterically that the thing will fall over. But that is because they
haven't put their minds in gear and are simply assuming that such a
trike will be built to the same dimensions and perverted principles of
current offerings.

WHY DO TRIKES TURN OVER?
Vehicles need a point to flip themselves over sideways: something must
dig in to cause the flip.

Bicycles and motorbikes cannot reach the sticking point that leads to
the flip because their weight and payload lies directly in line with
the wheels under virtually all conditions of tilt; when traction is
lost, the wheels slide away.

The roll centre is defined on the centre line of a multiwheel vehicle
by the suspensions linkages. The centre of gravity is defined by the
distribution of masses in the vehicle; think of it as the pivot of the
scales (a three-dimensional definition is below).

On a fourwheel vehicle the sticking-point is the line between the
centres of the contact patches of the tires of the front and rear
wheels on the inside of the corner. When the weight of the vehicle
reacts with the centripetal force through the roll centre to shift the
centre of gravity of the vehicle and payload outside this line, it
flips: the scales are no longer balanced. It's a little more
complicated than that but for bicycle tires with tiny contact patches
and in an application where zero-scrub radius is in any event de
riguer, we can take the tire centreline as the datum point.

In real life the centre of gravity of the vehicle (including its
occupant) is defined in three dimensions. On a tricycle for one
occupant it very likely falls on the longitudinal centreline, so we
need only to know where the CoG resides at standstill on the wheelbase
and what its static height is. We will of course design suspension
linkages that control dive under braking and squat under acceleration,
so that all that concerns us now is the sideways movement of the CoG
in a turn.

The flipover line on a tricyle runs between the centres of the contact
patches of the front inside tyre in the corner and the single rear
tyre. Thus, to make the thing corner well, it is necessary to move the
CoG as near to over the front axle as is possible in order to get it
as far as possible from the flipover barrier. This is impossible to do
if the rider's feet are to be inside the wheelbase or at least not too
far in front of the front axle line. But there are many ways to skin a
cat if the designer doesn't allow current practice to handcuff him to
fashionable stupidities.

FIRST SOLUTION TO A COMFORTABLE UTILITY TRIKE
We're still assuming a trike with the seat at office height and common
29er balloon wheels. The seat height determines the hub height and
therefore the size of the wheel/tyre combination.

We need the large wheels because, though in theory we can attach
control arms anywhere along the height of the wheel, in practice (and
most especially on a bicycle where ounces count!), the control arms,
which determine the start position of the centre of gravity and its
sideways motion, are best disposed around the vertical centre of the
wheel. 36 inch monocycle wheels, for which Croker can supply tyres,
would be even better because they would put the seat below the hubs,
but such wheels/tyres are less common so let's stick with the common
29er which puts the bottom of the seat at hub height.

Now, the wider the front track, and the longer the wheelbase (on a
tricycle), the further the centre of gravity has to travel to cross
the flipover line between the front and rear contact patches. Having
the bottom bracket inside the wheelbase together with a lowish seat
already makes for a long wheelbase, so that is taken care of.

For stability the track should be as wide as possible. The question
is, will the resulting vehicle be viewed as an invalid carriage, in
which case it should be narrow enough to fit on pavements, or will it
be a general utility vehicle with stability for fast corners on the
open road?

If stability on the open road is wanted, the track should be around
five feet, which would make the bicycle as wide as a small car.

Voila, we now have a tricycle with the seat at a comfortable height
and with stability around corners.

COMPARISON WITH EXISTING RECUMBENT TRIKE DESIGNS
The contortions of the current crop of recumbent trike designers are
seen to be injurious to their sales for no great advantage except that
in some extreme cases their tricycles are narrow enough to go on
pavements -- and in those cases my high but widebase design will kill
them around fast corners. Being aerodynamically fast is no use if the
aero advantage is brought about by being so narrow that the trike
flips in corners taken at more than moderate speed.

In short, current ultra-recumbent trikes are claimed to be extreme but
in fact are compromised on every aspect of performance.

COMPARING THE COMFORT-TRIKE WITH A TWO-WHEELER
At this point my comfortable trike suffers the same *competitive*
problem vis a vis two-wheelers around really fast corners as the
standard ultra-low trike available off the shelf right now from every
run-of-the-mill bent maker: a two-wheel bike is much faster around
corners under all but the least likely circumstances. A skilled and
brave rider on a two-wheeler on a dry road will be hanging in there
long after any tricycle, no matter how low and how wide, has flipped
over: this conclusion is inherent in the angling of the flipover line
between the front and rear wheels. You can see this conclusion easily
when you consider that a four-wheel human powered vehicle of the same
track as the tricycle will give the two-wheeler a much closer run for
its money -- and will still lose unless the track is made grotesquely
wide and the test is conducted on a very wide, uncambered surface (an
airport, a closed multilane road? -- see, we're talking about
extremes).

SECOND SOLUTION: MAKING THE COMFORTABLE TRICYCLE FAST
There is a way to make a trike or a quadricycle hang on to the road
after the two-wheeler has lost traction and balance and slid away in
the ditch. It is, historically, an accident of incompetent suspension
design, in which equal length, parallel wishbones (and other older
suspensions), failed to stop the body of the car tilting, and failed
to hold the wheel upright (the two prime desiderata of automobile
suspension design).

However, with narrow bicycle tyres on a human powered tricycle (or
quadricycle) it is desirable for the wheels and the body to tilt,
because in that way the vehicle can be made to emulate cycle leanover,
and thus hang on to traction longer and, most of all, avoid flipping
over longer, instead sliding. Such a vehicle is generally referred to
as "leaning" or "tilting".

The design requirements of a tilting tricycle or quadricycle are for
the most part simple to anyone with automobile experience: whatever
you learned is totally undesirable in a good racing car will make a
wonderful tilting vehicle!

A tilting vehicle must have its roll centre at ground level and
suspension linkages that allow the body to tilt in roll and the wheel
camber to change proportionally to the roll. That's easily taken care
of parallel, equal length wishbones. Tilting to 35 degrees from
horizontal seems reasonable. A tilting vehicle must have zero scrub
radius and this is easily taken care of by a somewhat extreme kingpin
inclination. Ackermann steering arm angles must be chosen with some
care to avoid the desire for reasonably light steering interfering
with the tilting. Suitable castor and trail to give a tilting vehicle
steering the correct self-centring and weight can be discovered on a
drawing or on a model or on the road by using adjustable links in the
suspension. Adjustable links would be desireable anyway to regulate
the degree of proportionality between roll and camber, that is, to
adjust the suspension ever so slightly away from equal length.
Progressive springing and damping at the front wheels, especially if
the progression is adjustable (a row of mounting points will do fine),
will help control the tilt for various amounts of steer angle. A
common disc brake on any swinging arm can be used to lock the tilting
at standstill.

It all sounds like a great deal of work with parameters which fight
each other, and it is, but the computer makes what was impossible well
within living memory not only easy but comparatively fast.

At this point we have a comfortable and practical tilting tricycle
which, unless it is grossly badly executed, will give a two-wheeler
real competion around a corner even in the dry, and which will shrug
off bad roads.

CAN A TILTING TRI/QUADRICYCLE BE PERFECT?
In theory, yes, if it has electricity for computing power and for
driving stepper motors; it might be possible to run electronic
controls for active tilting suspension off a hub dynamo. (Shimano has
long since commercialized active Di2 suspension forks and gear
changing run off a hub dynamo.) In practice, even powered tilting
devices do not yet respond perfectly to imperfect roads.

Strictly human-powered tilting vehicles with more than two wheels are
far from a solved problem. The difficulty is not tilting: on roads
cambered perfectly appropriately in turns, tilting can be automatic,
look ma, no hands; if such roads between turns were furthermore table-
flat, the perfect tilting trike would need no steering whatsoever.
Read that again: no steering. The problem is that no road is perfectly
flat, nor ever perfectly cambered, and no trike is perfectly built,
nor can the human passenger ever be perfectly symmetrical, sit
perfectly still on the straights or dispose of his weight perfectly
optimally in corners.

Steering is essential and will always be. But steering fights tilting.
In addition, one might wish the vehicle to tilt more or less than
dictated by the real-life camber on real-life roads (as distinct from
the ideal roads in the computer), for instance for something as simple
as a bumpy road or for cutting an apex, so a manual tilt control (in
addition to the stops built into the suspension to limit suspension
arm travel to a tilt of 35 degrees) is desirable. Complications and
weight start to mount, and even the simplest system has a learning
curve.

Riding a tilting tri/quadricycle will never be as intuitive as riding
a bicycle (for a start, the rider needs to set it up for the curve
like a bicycle by first momentarily turning the wrong way, which isn't
what happens in a normal multi-wheel vehicle like a car).

The tilting tri/quadricycle, which seemed simple in conception, has
now been mechanically complicated and weighted up quite a bit, and we
see that to make it work perfectly not only counterintuitive
techniques but also a dangerous new control (the tilt control) will
have to be learned. It is a dangerous control because overenthusiastic
or clumsy or ignorant use can achieve what the tilting mechanism is
intended to prevent, flip the vehicle over.

Or the designer can throw up his hands and say that for safe operation
and the least mechanical complication and light weight, he will
sacrifice theoretical perfections by building the tilting tri/
quadricycle with tilt (directly or indirectly) proportional to the
steering angle and thus controlled through the control already
familiar to riders, the steering.

IN SUMMARY
Current recumbent bicycles have betrayed their original impulse of a
butt-saver on which it was easy to sit down and get up. The same
applies to current recumbent trikes, whose single advantage of static
stability doesn't even apply dynamically to trikes with narrow tracks
(virtually all) for notional aero efficiency -- for what good is speed
if it flips the rider over on corners? Current recumbents are so
extreme (small wheels, groundhugging seats) that they are totally
impractical for everyday use.

It is possible to build a tricycle which is more practical by starting
with an office chair seat height and standard 29er wheels, and by
giving it a much wider track than is now common to make it faster
around corners than the current offerings. It will also seat the rider
high enough to make him feel more secure in traffic. While this
comfortable, practical tricycle by virtue of its wide track will be
faster around corners than the current recumbent trike offerings, it
will never be faster than two-wheelers. Another way of putting it is
that even this good and secure recumbent will always have a lower
cornering limit on good roads than a bicycle; it will only shine in
fast work in really bad conditions.

The good and practical trike can be made faster and more secure with
simple mechanical tilting. There is a learning requirement because
turn-in is different from other multi-wheeled vehicles the rider may
be familiar with. But a simple tilting trike or quadricycle should be
able to approach the cornering abilities of a bicycle on good roads
and exceed it on slippery roads (which means cow dung or mud or oil,
not just water on clean tarmac -- even balloon tyres have too small a
contact patch to hydroplane easily).

For more complication, weight and cost, variable tilting under the
control of the pilote is possible but there will be a steep learning
curve, and clumsy use could turn the controlled-tilting trike into a
more dangerous vehicle than the non-tilting or simple-tilting one.

CONCLUSION
On the whole then, current recumbents are simply fashion, not much
chop even for their stated purpose, perverted beyond any practical use
by their originally intended consumers, and even a good tricycle has
so few advantages that it is probably best limited to those with
balance problems or truly awful roads or for special purposes like
sand-sailing. If speed is required, simple tilting mechanisms on the
tricycle could move the roll-over speed in any corner upwards
appreciably.

Recumbents (two and three wheelers) are an unnecessary niche, nothing
but an extreme fashion accessory.

People (the old and the handicapped) who can truly benefit even from a
more practical tricycle as described above are likely to ride too
slowly to discover the speed advantages of a wide-track fast tadpole
and so should have high-seat tricycles with tracks narrow enough for
versatility on pavements and in doorways.

That makes even my practical, speedy trike design concept superfluous,
an interesting mental exercise of the type: "Well, we have trikes but
they don't deliver on their promises. Let's see if we can design one
that does." We can. So what?

Looks like I've wasted several days considering how recumbents can be
improved...

For the rest of us, it is not surprising that the diamond frame still
dominates. For those who want or need to put their feet flat on the
road without leaving the saddle or seat, the only small surprise is
that the Giant Revive did not survive, but it is no surprise that its
more traditional-appearing spiritual and geometric soul-sisters from
Electra and Trek and RANS are doing well, even becoming trendy. Nor is
it surprising that their makers eschew calling them what they are
(semi-recumbents) because the name "recumbent" is so discredited,
instead preferring "crank forward" or even the somewhat disturbing
"flatfoot".

IN THE END....
I conclude that the upright and the semi-recumbent bicycles and the
narrow wheelbase invalid carriage and the child's tricycle are
necessary human-power formats, and the rest (recumbents regardless of
number of wheels, plus my fast wide-track tadpole) are the unnecessary
jewelry of an excessive society.

Copyright 2009 Andre Jute
Free to use on not-for-profit netsites as longs the entire article,
including this notice, is reprinted intact. Any other use contact
author
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  #2  
Old June 3rd 09, 12:38 AM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
datakoll
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Posts: 7,793
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

ANYONE KNOW JUTE'S COORDINATES ?
  #3  
Old June 3rd 09, 12:43 AM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
AMuzi
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Posts: 9,835
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

datakoll wrote:
ANYONE KNOW JUTE'S COORDINATES ?


Those combined with Kim Jong Il's email address might have
some potential.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971
  #4  
Old June 3rd 09, 01:28 AM posted to alt.rec.bicycles.recumbent
gotbent[_8_]
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Posts: 29
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute


"Andre Jute" wrote in message
...
THE LOGIC OF TRIKES
an outsider's viewpoint
by Andre Jute

snippage of large volumes of trite verbiage

Andre. Andre, Andre, I'm speaking as someone who has an insider's viewpoint
and I must say that you've typed a term paper full of nonsense. You have an
intense prejudice against recumbent bicycles and have gone to great length
to show that, and have not made a single substantial argument that could
stand up the careful scrutiny of a peer review.


gotbent aka FRT rider



  #5  
Old June 3rd 09, 03:20 AM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
Edward Dolan
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Posts: 14,212
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute


"Andre Jute" wrote in message
...
THE LOGIC OF TRIKES

an outsider's viewpoint
by Andre Jute

When an uncommitted cyclist comes to look at recumbents, he sees

bicycles in which everything has been sacrificed for aerodynamic
advantage. Recumbents were originally presented as solving the problem
of the bike saddle, the last pressure point (pun intended) of diamond
frame design, by getting the rider's weight off his butt and onto his
back, and by lowering the seat on the bike to make it easier for older
people and the less nimble to mount and dismount. So much for good
intentions.
[...]

Blah, Blah, Blah ...

You must be an idiot to think anyone in his right mind would read your
exceedingly long, rambling, nonsensical post. Who do you think inhabits
these newsgroups anyway?

A message to a Usenet newsgroup is for making a single point only, and doing
it with as few words as possible. Because you do not have a clue about
anything, I can assure you that no one will read your post, let alone answer
any of it.

Regards,

Ed Dolan the Great - Minnesota
aka
Saint Edward the Great - Order of the Perpetual Sorrows - Minnesota





  #6  
Old June 3rd 09, 07:30 AM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
someone
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Posts: 2,340
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

On 3 June, 00:35, Andre Jute wrote:
THE LOGIC OF TRIKES


They tend to be a bit bigger than you first expect, and then some.

Wondered when the picnic basket would be mentioned along with 5 star
fuel and a linear engine, and where would it all fit?
  #7  
Old June 3rd 09, 04:27 PM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
Andre Jute[_2_]
external usenet poster
 
Posts: 8,818
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

On Jun 3, 7:30*am, someone wrote:
On 3 June, 00:35, Andre Jute wrote:

THE LOGIC OF TRIKES


They tend to be a bit bigger than you first expect, and then some.

Wondered when the picnic basket would be mentioned along with 5 star
fuel and a linear engine, and where would it all fit?


Never a truer word spoken in jest. I was lying in bed this afternoon
-- I sleep during the day and work at night -- thinking that the
tilting quadricycle I took as far as a dimensioned sketch in order to
work out the article below would make a wonderful cyclecar. Think
about it. With the suspension I sketched out at the front front and
triangulated parallel arms locating the rear hubs both transversely
longitudinally, the entire chassis could be two rails of one to one-
and-a-half inch pipe disposed vertically one above the other, with a
few triangulating crosses, and not very long either even as a tandem.
Two riders in tandem sitting on top of this frame, some exiguous
bodywork a la Bugatti T35, a motorbike engine centrally disposed under
the rear seat, and the whole thing could weigh well under 400 pounds
complete with bicycle fenders and a full fuel tank. Be a blast in my
lanes -- and we already have just the picnic basket too.

Actually, I've always thought it odd that my book "Designing and
Building Special Cars" (Batsford, London) is so popular with
Ultralight builders, as it was written on hand of the Bentleys I
turned into sports cars, my Panther Royale chassis, and my 155mph
desert cars -- the lightest thing in there is 120in wheelbase 4-seat
convertible with an ali chassis constructed of rectangular sections
large enough to double as body sides! I didn't become interested in
lightweight construction (meaning for road use, outside racing, lest
some idiot publishes an old photo of me working on a racing frame and
calls me a liar) until I had already given up the car to become a
cyclist. It would be ironic if via bicycles I were reborn as an
ultralight motorist...

Andre Jute
Visit Andre's books at
http://www.audio-talk.co.uk/fiultra/THE%20WRITER'S%20HOUSE.html

Original post:

THE LOGIC OF TRIKES
an outsider's viewpoint
by Andre Jute

When an uncommitted cyclist comes to look at recumbents, he sees
bicycles in which everything has been sacrificed for aerodynamic
advantage. Recumbents were originally presented as solving the problem
of the bike saddle, the last pressure point (pun intended) of diamond
frame design, by getting the rider's weight off his butt and onto his
back, and by lowering the seat on the bike to make it easier for older
people and the less nimble to mount and dismount. So much for good
intentions.

TWO WHEELERS
Beyond aero advantage -- and its resultant of speed -- two-wheel
recumbents have no advantage over a well-designed bicycle of
traditional geometry, even over the standard diamond frame.

They do however have a great many disadvantages. The greatest of these
is near-invisibility to drivers, symbolized by a flag on a flexible
antenna carried on many recumbents.

And designers have now taken the designs to such extremes that, far
from solving the problems of mounting and dismounting, recumbents
require distortions to mount and dismount, and a flexible spine even
to see the road from the extreme recumbent positions.

The mainstream of recumbents are in such a mess both as design and
marketing exercises that a whole new concept of so-called Compact Long
Wheelbase Semi-Recumbent bicycles was created to solve the same old
saddle and mounting problems all over again, of which the Giant Revive
is already off the market again, the USED Scooterbike isn't doing too
well, and the Utopia Phoenix sells well enough into its upmarket niche
recently to have been further developed.

RECUMBENT TRIKES
At first recumbent trikes seem to have an advantage: the stability of
three wheels. We can dismiss the socalled delta tricycles with the
single wheel at the front: they are inherently unstable when compared
like for like (wheel size and seat height) with the socalled tadpole
tricyles which carry the single wheel at the rear. We can also dismiss
the novelty of rear wheel steering as unsolved and very likely
inherently unstable.

Unfortunately, even on three wheels, designers have again gone to the
extremes for a sporting advantage and thereby frittered away the
advantage of the topology for everyone heyond the speedfreak minority.
In particular, they have gone for small wheels and consequently were
forced to install seats a very few inches off the ground, suitable
only for the young and flexible to drop into, from which no one can
rise gracefully. They have also, to gain the least frontal area, made
trikes pretty narrow (which again forces a very low seat to avoid the
thing overturning on the least taxing corner taken at low speed), so
that the nominal advantage of static stability doesn't carry over very
far into the dynamics of the trike in motion.

Because of the way trikes sacrifice everything for aerodynamics, I
have severe doubts whether any trike on the market will be faster
around a downhill corner than a recumbent bicycle with the same
frontal area. The road holding and handling of a two-wheeler will in
all respects be superior on a dry road and on clean wet roads too,
leaving the exceptional case of slippery roads (cow dung, mud) as the
natural milieu of the recumbent trike -- and who wants his face inches
above that ****?

OTHER COMMON PROBLEMS
Common recumbent two-wheelers and trikes place the rider's feet
vulnerably out in front of the wheels; you can forget riding these
things in mixed automobile and pedestrian traffic. You can't use them
for a dash across a piece of pavement as you can an upright bike.
Given that the rider's height on them is conducive to a feeling of
insecurity in traffic, that limits their use severely. I define a
utility bicycle as one the owner rides from his door on every
occasion; a bicycle that must be carried on an automobile to where one
can ride it is a novelty item, not a useful bike.

Because standard types of recumbents carry the feet way out in front
of the front wheels, the chainlines are grossly inefficient and ugly
and expensive to maintain. That alone is enough to condemn recumbents
for any thoughtful engineer.

CAN A COMFORTABLE AND STABLE TRIKE BE BUILT?
It may be possible. Posit a 29er trike with 700 wheels and balloon
tyres to reduce the spinging excursion at the rear wheel, and thereby
reduce damping and other control requirements, some of the less
obvious ones to be discussed below. Of course it is a tadpole, with
two wheels forward which steer and one at the rear which is driven.
The bottom bracket is on the swing arm carrying the rear wheel and
rear suspension, and the arm is pivoted in front of the bottom bracket
or concentrically with it so that the chain line is straight and
without idlers when an internal gear hub is used. Practically then the
crank must be behind the front axle which is in any event desirable
from a safety and psychological viewpoint. The seat can be put at the
same height as an office chair so that anyone can sit down gracefully
on it and rise equally gracefully from it.

At this point the recumbent faithful will start screeching
hysterically that the thing will fall over. But that is because they
haven't put their minds in gear and are simply assuming that such a
trike will be built to the same dimensions and perverted principles of
current offerings.

WHY DO TRIKES TURN OVER?
Vehicles need a point to flip themselves over sideways: something must
dig in to cause the flip.

Bicycles and motorbikes cannot reach the sticking point that leads to
the flip because their weight and payload lies directly in line with
the wheels under virtually all conditions of tilt; when traction is
lost, the wheels slide away.

The roll centre is defined on the centre line of a multiwheel vehicle
by the suspensions linkages. The centre of gravity is defined by the
distribution of masses in the vehicle; think of it as the pivot of the
scales (a three-dimensional definition is below).

On a fourwheel vehicle the sticking-point is the line between the
centres of the contact patches of the tires of the front and rear
wheels on the inside of the corner. When the weight of the vehicle
reacts with the centripetal force through the roll centre to shift the
centre of gravity of the vehicle and payload outside this line, it
flips: the scales are no longer balanced. It's a little more
complicated than that but for bicycle tires with tiny contact patches
and in an application where zero-scrub radius is in any event de
riguer, we can take the tire centreline as the datum point.

In real life the centre of gravity of the vehicle (including its
occupant) is defined in three dimensions. On a tricycle for one
occupant it very likely falls on the longitudinal centreline, so we
need only to know where the CoG resides at standstill on the wheelbase
and what its static height is. We will of course design suspension
linkages that control dive under braking and squat under acceleration,
so that all that concerns us now is the sideways movement of the CoG
in a turn.

The flipover line on a tricyle runs between the centres of the contact
patches of the front inside tyre in the corner and the single rear
tyre. Thus, to make the thing corner well, it is necessary to move the
CoG as near to over the front axle as is possible in order to get it
as far as possible from the flipover barrier. This is impossible to do
if the rider's feet are to be inside the wheelbase or at least not too
far in front of the front axle line. But there are many ways to skin a
cat if the designer doesn't allow current practice to handcuff him to
fashionable stupidities.

FIRST SOLUTION TO A COMFORTABLE UTILITY TRIKE
We're still assuming a trike with the seat at office height and common
29er balloon wheels. The seat height determines the hub height and
therefore the size of the wheel/tyre combination.

We need the large wheels because, though in theory we can attach
control arms anywhere along the height of the wheel, in practice (and
most especially on a bicycle where ounces count!), the control arms,
which determine the start position of the centre of gravity and its
sideways motion, are best disposed around the vertical centre of the
wheel. 36 inch monocycle wheels, for which Croker can supply tyres,
would be even better because they would put the seat below the hubs,
but such wheels/tyres are less common so let's stick with the common
29er which puts the bottom of the seat at hub height.

Now, the wider the front track, and the longer the wheelbase (on a
tricycle), the further the centre of gravity has to travel to cross
the flipover line between the front and rear contact patches. Having
the bottom bracket inside the wheelbase together with a lowish seat
already makes for a long wheelbase, so that is taken care of.

For stability the track should be as wide as possible. The question
is, will the resulting vehicle be viewed as an invalid carriage, in
which case it should be narrow enough to fit on pavements, or will it
be a general utility vehicle with stability for fast corners on the
open road?

If stability on the open road is wanted, the track should be around
five feet, which would make the bicycle as wide as a small car.

Voila, we now have a tricycle with the seat at a comfortable height
and with stability around corners.

COMPARISON WITH EXISTING RECUMBENT TRIKE DESIGNS
The contortions of the current crop of recumbent trike designers are
seen to be injurious to their sales for no great advantage except that
in some extreme cases their tricycles are narrow enough to go on
pavements -- and in those cases my high but widebase design will kill
them around fast corners. Being aerodynamically fast is no use if the
aero advantage is brought about by being so narrow that the trike
flips in corners taken at more than moderate speed.

In short, current ultra-recumbent trikes are claimed to be extreme but
in fact are compromised on every aspect of performance.

COMPARING THE COMFORT-TRIKE WITH A TWO-WHEELER
At this point my comfortable trike suffers the same *competitive*
problem vis a vis two-wheelers around really fast corners as the
standard ultra-low trike available off the shelf right now from every
run-of-the-mill bent maker: a two-wheel bike is much faster around
corners under all but the least likely circumstances. A skilled and
brave rider on a two-wheeler on a dry road will be hanging in there
long after any tricycle, no matter how low and how wide, has flipped
over: this conclusion is inherent in the angling of the flipover line
between the front and rear wheels. You can see this conclusion easily
when you consider that a four-wheel human powered vehicle of the same
track as the tricycle will give the two-wheeler a much closer run for
its money -- and will still lose unless the track is made grotesquely
wide and the test is conducted on a very wide, uncambered surface (an
airport, a closed multilane road? -- see, we're talking about
extremes).

SECOND SOLUTION: MAKING THE COMFORTABLE TRICYCLE FAST
There is a way to make a trike or a quadricycle hang on to the road
after the two-wheeler has lost traction and balance and slid away in
the ditch. It is, historically, an accident of incompetent suspension
design, in which equal length, parallel wishbones (and other older
suspensions), failed to stop the body of the car tilting, and failed
to hold the wheel upright (the two prime desiderata of automobile
suspension design).

However, with narrow bicycle tyres on a human powered tricycle (or
quadricycle) it is desirable for the wheels and the body to tilt,
because in that way the vehicle can be made to emulate cycle leanover,
and thus hang on to traction longer and, most of all, avoid flipping
over longer, instead sliding. Such a vehicle is generally referred to
as "leaning" or "tilting".

The design requirements of a tilting tricycle or quadricycle are for
the most part simple to anyone with automobile experience: whatever
you learned is totally undesirable in a good racing car will make a
wonderful tilting vehicle!

A tilting vehicle must have its roll centre at ground level and
suspension linkages that allow the body to tilt in roll and the wheel
camber to change proportionally to the roll. That's easily taken care
of parallel, equal length wishbones. Tilting to 35 degrees from
horizontal seems reasonable. A tilting vehicle must have zero scrub
radius and this is easily taken care of by a somewhat extreme kingpin
inclination. Ackermann steering arm angles must be chosen with some
care to avoid the desire for reasonably light steering interfering
with the tilting. Suitable castor and trail to give a tilting vehicle
steering the correct self-centring and weight can be discovered on a
drawing or on a model or on the road by using adjustable links in the
suspension. Adjustable links would be desireable anyway to regulate
the degree of proportionality between roll and camber, that is, to
adjust the suspension ever so slightly away from equal length.
Progressive springing and damping at the front wheels, especially if
the progression is adjustable (a row of mounting points will do fine),
will help control the tilt for various amounts of steer angle. A
common disc brake on any swinging arm can be used to lock the tilting
at standstill.

It all sounds like a great deal of work with parameters which fight
each other, and it is, but the computer makes what was impossible well
within living memory not only easy but comparatively fast.

At this point we have a comfortable and practical tilting tricycle
which, unless it is grossly badly executed, will give a two-wheeler
real competion around a corner even in the dry, and which will shrug
off bad roads.

CAN A TILTING TRI/QUADRICYCLE BE PERFECT?
In theory, yes, if it has electricity for computing power and for
driving stepper motors; it might be possible to run electronic
controls for active tilting suspension off a hub dynamo. (Shimano has
long since commercialized active Di2 suspension forks and gear
changing run off a hub dynamo.) In practice, even powered tilting
devices do not yet respond perfectly to imperfect roads.

Strictly human-powered tilting vehicles with more than two wheels are
far from a solved problem. The difficulty is not tilting: on roads
cambered perfectly appropriately in turns, tilting can be automatic,
look ma, no hands; if such roads between turns were furthermore table-
flat, the perfect tilting trike would need no steering whatsoever.
Read that again: no steering. The problem is that no road is perfectly
flat, nor ever perfectly cambered, and no trike is perfectly built,
nor can the human passenger ever be perfectly symmetrical, sit
perfectly still on the straights or dispose of his weight perfectly
optimally in corners.

Steering is essential and will always be. But steering fights tilting.
In addition, one might wish the vehicle to tilt more or less than
dictated by the real-life camber on real-life roads (as distinct from
the ideal roads in the computer), for instance for something as simple
as a bumpy road or for cutting an apex, so a manual tilt control (in
addition to the stops built into the suspension to limit suspension
arm travel to a tilt of 35 degrees) is desirable. Complications and
weight start to mount, and even the simplest system has a learning
curve.

Riding a tilting tri/quadricycle will never be as intuitive as riding
a bicycle (for a start, the rider needs to set it up for the curve
like a bicycle by first momentarily turning the wrong way, which isn't
what happens in a normal multi-wheel vehicle like a car).

The tilting tri/quadricycle, which seemed simple in conception, has
now been mechanically complicated and weighted up quite a bit, and we
see that to make it work perfectly not only counterintuitive
techniques but also a dangerous new control (the tilt control) will
have to be learned. It is a dangerous control because overenthusiastic
or clumsy or ignorant use can achieve what the tilting mechanism is
intended to prevent, flip the vehicle over.

Or the designer can throw up his hands and say that for safe operation
and the least mechanical complication and light weight, he will
sacrifice theoretical perfections by building the tilting tri/
quadricycle with tilt (directly or indirectly) proportional to the
steering angle and thus controlled through the control already
familiar to riders, the steering.

IN SUMMARY
Current recumbent bicycles have betrayed their original impulse of a
butt-saver on which it was easy to sit down and get up. The same
applies to current recumbent trikes, whose single advantage of static
stability doesn't even apply dynamically to trikes with narrow tracks
(virtually all) for notional aero efficiency -- for what good is speed
if it flips the rider over on corners? Current recumbents are so
extreme (small wheels, groundhugging seats) that they are totally
impractical for everyday use.

It is possible to build a tricycle which is more practical by starting
with an office chair seat height and standard 29er wheels, and by
giving it a much wider track than is now common to make it faster
around corners than the current offerings. It will also seat the rider
high enough to make him feel more secure in traffic. While this
comfortable, practical tricycle by virtue of its wide track will be
faster around corners than the current recumbent trike offerings, it
will never be faster than two-wheelers. Another way of putting it is
that even this good and secure recumbent will always have a lower
cornering limit on good roads than a bicycle; it will only shine in
fast work in really bad conditions.

The good and practical trike can be made faster and more secure with
simple mechanical tilting. There is a learning requirement because
turn-in is different from other multi-wheeled vehicles the rider may
be familiar with. But a simple tilting trike or quadricycle should be
able to approach the cornering abilities of a bicycle on good roads
and exceed it on slippery roads (which means cow dung or mud or oil,
not just water on clean tarmac -- even balloon tyres have too small a
contact patch to hydroplane easily).

For more complication, weight and cost, variable tilting under the
control of the pilote is possible but there will be a steep learning
curve, and clumsy use could turn the controlled-tilting trike into a
more dangerous vehicle than the non-tilting or simple-tilting one.

CONCLUSION
On the whole then, current recumbents are simply fashion, not much
chop even for their stated purpose, perverted beyond any practical use
by their originally intended consumers, and even a good tricycle has
so few advantages that it is probably best limited to those with
balance problems or truly awful roads or for special purposes like
sand-sailing. If speed is required, simple tilting mechanisms on the
tricycle could move the roll-over speed in any corner upwards
appreciably.

Recumbents (two and three wheelers) are an unnecessary niche, nothing
but an extreme fashion accessory.

People (the old and the handicapped) who can truly benefit even from a
more practical tricycle as described above are likely to ride too
slowly to discover the speed advantages of a wide-track fast tadpole
and so should have high-seat tricycles with tracks narrow enough for
versatility on pavements and in doorways.

That makes even my practical, speedy trike design concept superfluous,
an interesting mental exercise of the type: "Well, we have trikes but
they don't deliver on their promises. Let's see if we can design one
that does." We can. So what?

Looks like I've wasted several days considering how recumbents can be
improved...

For the rest of us, it is not surprising that the diamond frame still
dominates. For those who want or need to put their feet flat on the
road without leaving the saddle or seat, the only small surprise is
that the Giant Revive did not survive, but it is no surprise that its
more traditional-appearing spiritual and geometric soul-sisters from
Electra and Trek and RANS are doing well, even becoming trendy. Nor is
it surprising that their makers eschew calling them what they are
(semi-recumbents) because the name "recumbent" is so discredited,
instead preferring "crank forward" or even the somewhat disturbing
"flatfoot".

IN THE END....
I conclude that the upright and the semi-recumbent bicycles and the
narrow wheelbase invalid carriage and the child's tricycle are
necessary human-power formats, and the rest (recumbents regardless of
number of wheels, plus my fast wide-track tadpole) are the unnecessary
jewelry of an excessive society.

Copyright 2009 Andre Jute
Free to use on not-for-profit netsites as longs the entire article,
including this notice, is reprinted intact. Any other use contact
author

  #8  
Old June 3rd 09, 06:13 PM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
Opus[_2_]
external usenet poster
 
Posts: 414
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

On Jun 2, 11:35 pm, Andre Jute wrote:
THE LOGIC OF TRIKES
an outsider's viewpoint
by Andre Jute
snip
We can also dismiss
the novelty of rear wheel steering as unsolved and very likely
inherently unstable.

Actually the rear-steered tadpole design has been studied to death
since the late 1920s and was in wide use for decades as the landing
gear for airplanes. All it takes is the willingness to look outside a
particular application to other fields that use a similar layout. In
aircraft the parameters if CG height, distance of CG behind the front
wheels, maximum lateral acceleration, and what happens when the limits
of adhesion are exceeded at any of the three wheels have been in the
hot-rodder's parlance "scienced out". By staying within certain ratios
of CG height to track width, and front/rear balance a rear steer
tadpole can be a stable machine with quirks that can be manage with
operator experience, much like a single-track machine.
snip

Because standard types of recumbents carry the feet way out in front
of the front wheels, the chainlines are grossly inefficient and ugly
and expensive to maintain. That alone is enough to condemn recumbents
for any thoughtful engineer.

I don't see recumbent chains as having any more problems than chains
for DF bikes aside from the length needed to get from cranks to drive
wheels and the only additional expense I have seen has been the
requirement for frequent lubrication and cleaning to avoid having to
replace the chain, and the expense of buying multiple pre-packaged
chains to service a single machine.

CAN A COMFORTABLE AND STABLE TRIKE BE BUILT?
It may be possible. Posit a 29er trike with 700 wheels and balloon
tyres to reduce the spinging excursion at the rear wheel, and thereby
reduce damping and other control requirements, some of the less
obvious ones to be discussed below. Of course it is a tadpole, with
two wheels forward which steer and one at the rear which is driven.
The bottom bracket is on the swing arm carrying the rear wheel and
rear suspension, and the arm is pivoted in front of the bottom bracket
or concentrically with it so that the chain line is straight and
without idlers when an internal gear hub is used. Practically then the
crank must be behind the front axle which is in any event desirable
from a safety and psychological viewpoint. The seat can be put at the
same height as an office chair so that anyone can sit down gracefully
on it and rise equally gracefully from it.

At this point the recumbent faithful will start screeching
hysterically that the thing will fall over. But that is because they
haven't put their minds in gear and are simply assuming that such a
trike will be built to the same dimensions and perverted principles of
current offerings.

WHY DO TRIKES TURN OVER?
Vehicles need a point to flip themselves over sideways: something must
dig in to cause the flip.

Bicycles and motorbikes cannot reach the sticking point that leads to
the flip because their weight and payload lies directly in line with
the wheels under virtually all conditions of tilt; when traction is
lost, the wheels slide away.

The roll centre is defined on the centre line of a multiwheel vehicle
by the suspensions linkages. The centre of gravity is defined by the
distribution of masses in the vehicle; think of it as the pivot of the
scales (a three-dimensional definition is below).

On a fourwheel vehicle the sticking-point is the line between the
centres of the contact patches of the tires of the front and rear
wheels on the inside of the corner. When the weight of the vehicle
reacts with the centripetal force through the roll centre to shift the
centre of gravity of the vehicle and payload outside this line, it
flips: the scales are no longer balanced. It's a little more
complicated than that but for bicycle tires with tiny contact patches
and in an application where zero-scrub radius is in any event de
riguer, we can take the tire centreline as the datum point.

OK that is just a bunch of hogwash. The tipover point for a multi-
track vehicle is determined by the ratio of the CG height to the track
width, or in the case of a delta or tadpole trike the effective track
width at the CG location (that would be the CG distance from the
paired wheels over the wheelbase times the track width, or in graphic
terms the width of a pair of lines drawn between the contact points of
the front and rear wheels at the CG). When the lateral acceleration
causes the force on the CG times the CG height divided by half the
track to exceed the static load on the inside wheel of a turn or the
uphill wheel of a side hill vehicle then the wheel will lift and if
traction is maintained the vehicle will turn over. That is it.
Suspension linkages can only make this happen sooner rather than later
by causing the sideways motion of the vehicle load away from the
inside wheel. This is why Karts are some of the best handling vehicles
in racing. No suspension no messing up the pure relationship between
speed and tip over, which allows a driver to develop the feel of when
a vehicle is going to either slide or tip over.

Opus
  #9  
Old June 3rd 09, 07:57 PM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
Andre Jute[_2_]
external usenet poster
 
Posts: 8,818
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute

On Jun 3, 6:13*pm, Opus wrote:
On Jun 2, 11:35 pm, Andre Jute wrote: THE LOGIC OF TRIKES
an outsider's viewpoint
by Andre Jute
snip
We can also dismiss
the novelty of rear wheel steering as unsolved and very likely
inherently unstable.


Actually the rear-steered tadpole design has been studied to death
since the late 1920s and was in wide use for decades as the landing
gear for airplanes. All it takes is the willingness to look outside a
particular application to other fields that use a similar layout. In
aircraft the parameters if CG height, distance of CG behind the front
wheels, maximum lateral acceleration, and what happens when the limits
of adhesion are exceeded at any of the three wheels have been in the
hot-rodder's parlance "scienced out". By staying within certain ratios
of CG height to track width, and front/rear balance a rear steer
tadpole can be a stable machine with quirks that can be manage with
operator experience, much like a single-track machine.snip

Because standard types of recumbents carry the feet way out in front
of the front wheels, the chainlines are grossly inefficient and ugly
and expensive to maintain. That alone is enough to condemn recumbents
for any thoughtful engineer.


I don't see recumbent chains as having any more problems than chains
for DF bikes aside from the length needed to get from cranks to drive
wheels and the only additional expense I have seen has been the
requirement for frequent lubrication and cleaning to avoid having to
replace the chain, and the expense of buying multiple pre-packaged
chains to service a single machine.


You don't consider those disadvantages? It's your list, pal, not mine,
but I must tell you that my bikes have chains serviced twice a year
that last almost forever. Anything less is an imposition on my time
and patience by an incompetent designer.

CAN A COMFORTABLE AND STABLE TRIKE BE BUILT?
It may be possible. Posit a 29er trike with 700 wheels and balloon
tyres to reduce the spinging excursion at the rear wheel, and thereby
reduce damping and other control requirements, some of the less
obvious ones to be discussed below. Of course it is a tadpole, with
two wheels forward which steer and one at the rear which is driven.
The bottom bracket is on the swing arm carrying the rear wheel and
rear suspension, and the arm is pivoted in front of the bottom bracket
or concentrically with it so that the chain line is straight and
without idlers when an internal gear hub is used. Practically then the
crank must be behind the front axle which is in any event desirable
from a safety and psychological viewpoint. The seat can be put at the
same height as an office chair so that anyone can sit down gracefully
on it and rise equally gracefully from it.


At this point the recumbent faithful will start screeching
hysterically that the thing will fall over. But that is because they
haven't put their minds in gear and are simply assuming that such a
trike will be built to the same dimensions and perverted principles of
current offerings.


WHY DO TRIKES TURN OVER?
Vehicles need a point to flip themselves over sideways: something must
dig in to cause the flip.


Bicycles and motorbikes cannot reach the sticking point that leads to
the flip because their weight and payload lies directly in line with
the wheels under virtually all conditions of tilt; when traction is
lost, the wheels slide away.


The roll centre is defined on the centre line of a multiwheel vehicle
by the suspensions linkages. The centre of gravity is defined by the
distribution of masses in the vehicle; think of it as the pivot of the
scales (a three-dimensional definition is below).


On a fourwheel vehicle the sticking-point is the line between the
centres of the contact patches of the tires of the front and rear
wheels on the inside of the corner. When the weight of the vehicle
reacts with the centripetal force through the roll centre to shift the
centre of gravity of the vehicle and payload outside this line, it
flips: the scales are no longer balanced. *It's a little more
complicated than that but for bicycle tires with tiny contact patches
and in an application where zero-scrub radius is in any event de
riguer, *we can take the tire centreline as the datum point.


OK that is just a bunch of hogwash.


Okay, let's see you do better.

The tipover point for a multi-
track vehicle is determined by the ratio of the CG height to the track
width, or in the case of a delta or tadpole trike the effective track
width at the CG location (that would be the CG distance from the
paired wheels over the wheelbase times the track width, or in graphic
terms the width of a pair of lines drawn between the contact points of
the front and rear wheels at the CG).


Yes, that's what I said, but you cut it away. Here it is again:
"The flipover line on a tricyle runs between the centres of the
contact
patches of the front inside tyre in the corner and the single rear
tyre. Thus, to make the thing corner well, it is necessary to move
the
CoG as near to over the front axle as is possible in order to get it
as far as possible from the flipover barrier. This is impossible to
do
if the rider's feet are to be inside the wheelbase or at least not
too
far in front of the front axle line. But there are many ways to skin
a
cat if the designer doesn't allow current practice to handcuff him to
fashionable stupidities."

When the lateral acceleration
causes the force on the CG times the CG height divided by half the
track to exceed the static load on the inside wheel of a turn or the
uphill wheel of a side hill vehicle then the wheel will lift and if
traction is maintained the vehicle will turn over. That is it.


Yes, that's what I said, except I applied it to tricycles, if one puts
the kindest possible interpretation on the hogwash you actually wrote:
"or the uphill wheel of a side hill vehicle". What, for heaven's sake,
is a "side hill vehicle"?

Suspension linkages can only make this happen sooner rather than later
by causing the sideways motion of the vehicle load away from the
inside wheel. This is why Karts are some of the best handling vehicles
in racing. No suspension no messing up the pure relationship between
speed and tip over, which allows a driver to develop the feel of when
a vehicle is going to either slide or tip over.


This is wrong, probably arising from your expectation that any
suspension applied will result in a roll centre above ground. In the
text you cut away I explain carefully that an older suspension, equal
length parallel arms, put the roll centre at ground level, thus making
it relatively harder for the vehicle to overturn. You have fallen into
the same trap you warn me about above, where you talk of rear wheel
steering on aircraft. Note that it is even possible to move the roll
centre below ground.

Here is my full post again; it is internally and externally coherent
and when you snip it carelessly, you make mistakes like the ones
above.

****
THE LOGIC OF TRIKES
an outsider's viewpoint
by Andre Jute
When an uncommitted cyclist comes to look at recumbents, he sees
bicycles in which everything has been sacrificed for aerodynamic
advantage. Recumbents were originally presented as solving the
problem
of the bike saddle, the last pressure point (pun intended) of diamond
frame design, by getting the rider's weight off his butt and onto his
back, and by lowering the seat on the bike to make it easier for
older
people and the less nimble to mount and dismount. So much for good
intentions.
TWO WHEELERS
Beyond aero advantage -- and its resultant of speed -- two-wheel
recumbents have no advantage over a well-designed bicycle of
traditional geometry, even over the standard diamond frame.
They do however have a great many disadvantages. The greatest of
these
is near-invisibility to drivers, symbolized by a flag on a flexible
antenna carried on many recumbents.
And designers have now taken the designs to such extremes that, far
from solving the problems of mounting and dismounting, recumbents
require distortions to mount and dismount, and a flexible spine even
to see the road from the extreme recumbent positions.
The mainstream of recumbents are in such a mess both as design and
marketing exercises that a whole new concept of so-called Compact
Long
Wheelbase Semi-Recumbent bicycles was created to solve the same old
saddle and mounting problems all over again, of which the Giant
Revive
is already off the market again, the USED Scooterbike isn't doing too
well, and the Utopia Phoenix sells well enough into its upmarket
niche
recently to have been further developed.
RECUMBENT TRIKES
At first recumbent trikes seem to have an advantage: the stability of
three wheels. We can dismiss the socalled delta tricycles with the
single wheel at the front: they are inherently unstable when compared
like for like (wheel size and seat height) with the socalled tadpole
tricyles which carry the single wheel at the rear. We can also
dismiss
the novelty of rear wheel steering as unsolved and very likely
inherently unstable.
Unfortunately, even on three wheels, designers have again gone to the
extremes for a sporting advantage and thereby frittered away the
advantage of the topology for everyone heyond the speedfreak
minority.
In particular, they have gone for small wheels and consequently were
forced to install seats a very few inches off the ground, suitable
only for the young and flexible to drop into, from which no one can
rise gracefully. They have also, to gain the least frontal area, made
trikes pretty narrow (which again forces a very low seat to avoid the
thing overturning on the least taxing corner taken at low speed), so
that the nominal advantage of static stability doesn't carry over
very
far into the dynamics of the trike in motion.
Because of the way trikes sacrifice everything for aerodynamics, I
have severe doubts whether any trike on the market will be faster
around a downhill corner than a recumbent bicycle with the same
frontal area. The road holding and handling of a two-wheeler will in
all respects be superior on a dry road and on clean wet roads too,
leaving the exceptional case of slippery roads (cow dung, mud) as the
natural milieu of the recumbent trike -- and who wants his face
inches
above that ****?
OTHER COMMON PROBLEMS
Common recumbent two-wheelers and trikes place the rider's feet
vulnerably out in front of the wheels; you can forget riding these
things in mixed automobile and pedestrian traffic. You can't use them
for a dash across a piece of pavement as you can an upright bike.
Given that the rider's height on them is conducive to a feeling of
insecurity in traffic, that limits their use severely. I define a
utility bicycle as one the owner rides from his door on every
occasion; a bicycle that must be carried on an automobile to where
one
can ride it is a novelty item, not a useful bike.
Because standard types of recumbents carry the feet way out in front
of the front wheels, the chainlines are grossly inefficient and ugly
and expensive to maintain. That alone is enough to condemn recumbents
for any thoughtful engineer.
CAN A COMFORTABLE AND STABLE TRIKE BE BUILT?
It may be possible. Posit a 29er trike with 700 wheels and balloon
tyres to reduce the spinging excursion at the rear wheel, and thereby
reduce damping and other control requirements, some of the less
obvious ones to be discussed below. Of course it is a tadpole, with
two wheels forward which steer and one at the rear which is driven.
The bottom bracket is on the swing arm carrying the rear wheel and
rear suspension, and the arm is pivoted in front of the bottom
bracket
or concentrically with it so that the chain line is straight and
without idlers when an internal gear hub is used. Practically then
the
crank must be behind the front axle which is in any event desirable
from a safety and psychological viewpoint. The seat can be put at the
same height as an office chair so that anyone can sit down gracefully
on it and rise equally gracefully from it.
At this point the recumbent faithful will start screeching
hysterically that the thing will fall over. But that is because they
haven't put their minds in gear and are simply assuming that such a
trike will be built to the same dimensions and perverted principles
of
current offerings.
WHY DO TRIKES TURN OVER?
Vehicles need a point to flip themselves over sideways: something
must
dig in to cause the flip.
Bicycles and motorbikes cannot reach the sticking point that leads to
the flip because their weight and payload lies directly in line with
the wheels under virtually all conditions of tilt; when traction is
lost, the wheels slide away.
The roll centre is defined on the centre line of a multiwheel vehicle
by the suspensions linkages. The centre of gravity is defined by the
distribution of masses in the vehicle; think of it as the pivot of
the
scales (a three-dimensional definition is below).
On a fourwheel vehicle the sticking-point is the line between the
centres of the contact patches of the tires of the front and rear
wheels on the inside of the corner. When the weight of the vehicle
reacts with the centripetal force through the roll centre to shift
the
centre of gravity of the vehicle and payload outside this line, it
flips: the scales are no longer balanced. It's a little more
complicated than that but for bicycle tires with tiny contact patches
and in an application where zero-scrub radius is in any event de
riguer, we can take the tire centreline as the datum point.
In real life the centre of gravity of the vehicle (including its
occupant) is defined in three dimensions. On a tricycle for one
occupant it very likely falls on the longitudinal centreline, so we
need only to know where the CoG resides at standstill on the
wheelbase
and what its static height is. We will of course design suspension
linkages that control dive under braking and squat under
acceleration,
so that all that concerns us now is the sideways movement of the CoG
in a turn.
The flipover line on a tricyle runs between the centres of the
contact
patches of the front inside tyre in the corner and the single rear
tyre. Thus, to make the thing corner well, it is necessary to move
the
CoG as near to over the front axle as is possible in order to get it
as far as possible from the flipover barrier. This is impossible to
do
if the rider's feet are to be inside the wheelbase or at least not
too
far in front of the front axle line. But there are many ways to skin
a
cat if the designer doesn't allow current practice to handcuff him to
fashionable stupidities.
FIRST SOLUTION TO A COMFORTABLE UTILITY TRIKE
We're still assuming a trike with the seat at office height and
common
29er balloon wheels. The seat height determines the hub height and
therefore the size of the wheel/tyre combination.
We need the large wheels because, though in theory we can attach
control arms anywhere along the height of the wheel, in practice (and
most especially on a bicycle where ounces count!), the control arms,
which determine the start position of the centre of gravity and its
sideways motion, are best disposed around the vertical centre of the
wheel. 36 inch monocycle wheels, for which Croker can supply tyres,
would be even better because they would put the seat below the hubs,
but such wheels/tyres are less common so let's stick with the common
29er which puts the bottom of the seat at hub height.
Now, the wider the front track, and the longer the wheelbase (on a
tricycle), the further the centre of gravity has to travel to cross
the flipover line between the front and rear contact patches. Having
the bottom bracket inside the wheelbase together with a lowish seat
already makes for a long wheelbase, so that is taken care of.
For stability the track should be as wide as possible. The question
is, will the resulting vehicle be viewed as an invalid carriage, in
which case it should be narrow enough to fit on pavements, or will it
be a general utility vehicle with stability for fast corners on the
open road?
If stability on the open road is wanted, the track should be around
five feet, which would make the bicycle as wide as a small car.
Voila, we now have a tricycle with the seat at a comfortable height
and with stability around corners.
COMPARISON WITH EXISTING RECUMBENT TRIKE DESIGNS
The contortions of the current crop of recumbent trike designers are
seen to be injurious to their sales for no great advantage except
that
in some extreme cases their tricycles are narrow enough to go on
pavements -- and in those cases my high but widebase design will kill
them around fast corners. Being aerodynamically fast is no use if the
aero advantage is brought about by being so narrow that the trike
flips in corners taken at more than moderate speed.
In short, current ultra-recumbent trikes are claimed to be extreme
but
in fact are compromised on every aspect of performance.
COMPARING THE COMFORT-TRIKE WITH A TWO-WHEELER
At this point my comfortable trike suffers the same *competitive*
problem vis a vis two-wheelers around really fast corners as the
standard ultra-low trike available off the shelf right now from every
run-of-the-mill bent maker: a two-wheel bike is much faster around
corners under all but the least likely circumstances. A skilled and
brave rider on a two-wheeler on a dry road will be hanging in there
long after any tricycle, no matter how low and how wide, has flipped
over: this conclusion is inherent in the angling of the flipover line
between the front and rear wheels. You can see this conclusion easily
when you consider that a four-wheel human powered vehicle of the same
track as the tricycle will give the two-wheeler a much closer run for
its money -- and will still lose unless the track is made grotesquely
wide and the test is conducted on a very wide, uncambered surface (an
airport, a closed multilane road? -- see, we're talking about
extremes).
SECOND SOLUTION: MAKING THE COMFORTABLE TRICYCLE FAST
There is a way to make a trike or a quadricycle hang on to the road
after the two-wheeler has lost traction and balance and slid away in
the ditch. It is, historically, an accident of incompetent suspension
design, in which equal length, parallel wishbones (and other older
suspensions), failed to stop the body of the car tilting, and failed
to hold the wheel upright (the two prime desiderata of automobile
suspension design).
However, with narrow bicycle tyres on a human powered tricycle (or
quadricycle) it is desirable for the wheels and the body to tilt,
because in that way the vehicle can be made to emulate cycle
leanover,
and thus hang on to traction longer and, most of all, avoid flipping
over longer, instead sliding. Such a vehicle is generally referred to
as "leaning" or "tilting".
The design requirements of a tilting tricycle or quadricycle are for
the most part simple to anyone with automobile experience: whatever
you learned is totally undesirable in a good racing car will make a
wonderful tilting vehicle!
A tilting vehicle must have its roll centre at ground level and
suspension linkages that allow the body to tilt in roll and the wheel
camber to change proportionally to the roll. That's easily taken care
of parallel, equal length wishbones. Tilting to 35 degrees from
horizontal seems reasonable. A tilting vehicle must have zero scrub
radius and this is easily taken care of by a somewhat extreme kingpin
inclination. Ackermann steering arm angles must be chosen with some
care to avoid the desire for reasonably light steering interfering
with the tilting. Suitable castor and trail to give a tilting vehicle
steering the correct self-centring and weight can be discovered on a
drawing or on a model or on the road by using adjustable links in the
suspension. Adjustable links would be desireable anyway to regulate
the degree of proportionality between roll and camber, that is, to
adjust the suspension ever so slightly away from equal length.
Progressive springing and damping at the front wheels, especially if
the progression is adjustable (a row of mounting points will do
fine),
will help control the tilt for various amounts of steer angle. A
common disc brake on any swinging arm can be used to lock the tilting
at standstill.
It all sounds like a great deal of work with parameters which fight
each other, and it is, but the computer makes what was impossible
well
within living memory not only easy but comparatively fast.
At this point we have a comfortable and practical tilting tricycle
which, unless it is grossly badly executed, will give a two-wheeler
real competion around a corner even in the dry, and which will shrug
off bad roads.
CAN A TILTING TRI/QUADRICYCLE BE PERFECT?
In theory, yes, if it has electricity for computing power and for
driving stepper motors; it might be possible to run electronic
controls for active tilting suspension off a hub dynamo. (Shimano has
long since commercialized active Di2 suspension forks and gear
changing run off a hub dynamo.) In practice, even powered tilting
devices do not yet respond perfectly to imperfect roads.
Strictly human-powered tilting vehicles with more than two wheels are
far from a solved problem. The difficulty is not tilting: on roads
cambered perfectly appropriately in turns, tilting can be automatic,
look ma, no hands; if such roads between turns were furthermore
table-
flat, the perfect tilting trike would need no steering whatsoever.
Read that again: no steering. The problem is that no road is
perfectly
flat, nor ever perfectly cambered, and no trike is perfectly built,
nor can the human passenger ever be perfectly symmetrical, sit
perfectly still on the straights or dispose of his weight perfectly
optimally in corners.
Steering is essential and will always be. But steering fights
tilting.
In addition, one might wish the vehicle to tilt more or less than
dictated by the real-life camber on real-life roads (as distinct from
the ideal roads in the computer), for instance for something as
simple
as a bumpy road or for cutting an apex, so a manual tilt control (in
addition to the stops built into the suspension to limit suspension
arm travel to a tilt of 35 degrees) is desirable. Complications and
weight start to mount, and even the simplest system has a learning
curve.
Riding a tilting tri/quadricycle will never be as intuitive as riding
a bicycle (for a start, the rider needs to set it up for the curve
like a bicycle by first momentarily turning the wrong way, which
isn't
what happens in a normal multi-wheel vehicle like a car).
The tilting tri/quadricycle, which seemed simple in conception, has
now been mechanically complicated and weighted up quite a bit, and we
see that to make it work perfectly not only counterintuitive
techniques but also a dangerous new control (the tilt control) will
have to be learned. It is a dangerous control because
overenthusiastic
or clumsy or ignorant use can achieve what the tilting mechanism is
intended to prevent, flip the vehicle over.
Or the designer can throw up his hands and say that for safe
operation
and the least mechanical complication and light weight, he will
sacrifice theoretical perfections by building the tilting tri/
quadricycle with tilt (directly or indirectly) proportional to the
steering angle and thus controlled through the control already
familiar to riders, the steering.
IN SUMMARY
Current recumbent bicycles have betrayed their original impulse of a
butt-saver on which it was easy to sit down and get up. The same
applies to current recumbent trikes, whose single advantage of static
stability doesn't even apply dynamically to trikes with narrow tracks
(virtually all) for notional aero efficiency -- for what good is
speed
if it flips the rider over on corners? Current recumbents are so
extreme (small wheels, groundhugging seats) that they are totally
impractical for everyday use.
It is possible to build a tricycle which is more practical by
starting
with an office chair seat height and standard 29er wheels, and by
giving it a much wider track than is now common to make it faster
around corners than the current offerings. It will also seat the
rider
high enough to make him feel more secure in traffic. While this
comfortable, practical tricycle by virtue of its wide track will be
faster around corners than the current recumbent trike offerings, it
will never be faster than two-wheelers. Another way of putting it is
that even this good and secure recumbent will always have a lower
cornering limit on good roads than a bicycle; it will only shine in
fast work in really bad conditions.
The good and practical trike can be made faster and more secure with
simple mechanical tilting. There is a learning requirement because
turn-in is different from other multi-wheeled vehicles the rider may
be familiar with. But a simple tilting trike or quadricycle should be
able to approach the cornering abilities of a bicycle on good roads
and exceed it on slippery roads (which means cow dung or mud or oil,
not just water on clean tarmac -- even balloon tyres have too small a
contact patch to hydroplane easily).
For more complication, weight and cost, variable tilting under the
control of the pilote is possible but there will be a steep learning
curve, and clumsy use could turn the controlled-tilting trike into a
more dangerous vehicle than the non-tilting or simple-tilting one.
CONCLUSION
On the whole then, current recumbents are simply fashion, not much
chop even for their stated purpose, perverted beyond any practical
use
by their originally intended consumers, and even a good tricycle has
so few advantages that it is probably best limited to those with
balance problems or truly awful roads or for special purposes like
sand-sailing. If speed is required, simple tilting mechanisms on the
tricycle could move the roll-over speed in any corner upwards
appreciably.
Recumbents (two and three wheelers) are an unnecessary niche, nothing
but an extreme fashion accessory.
People (the old and the handicapped) who can truly benefit even from
a
more practical tricycle as described above are likely to ride too
slowly to discover the speed advantages of a wide-track fast tadpole
and so should have high-seat tricycles with tracks narrow enough for
versatility on pavements and in doorways.
That makes even my practical, speedy trike design concept
superfluous,
an interesting mental exercise of the type: "Well, we have trikes but
they don't deliver on their promises. Let's see if we can design one
that does." We can. So what?
Looks like I've wasted several days considering how recumbents can be
improved...
For the rest of us, it is not surprising that the diamond frame still
dominates. For those who want or need to put their feet flat on the
road without leaving the saddle or seat, the only small surprise is
that the Giant Revive did not survive, but it is no surprise that its
more traditional-appearing spiritual and geometric soul-sisters from
Electra and Trek and RANS are doing well, even becoming trendy. Nor
is
it surprising that their makers eschew calling them what they are
(semi-recumbents) because the name "recumbent" is so discredited,
instead preferring "crank forward" or even the somewhat disturbing
"flatfoot".
IN THE END....
I conclude that the upright and the semi-recumbent bicycles and the
narrow wheelbase invalid carriage and the child's tricycle are
necessary human-power formats, and the rest (recumbents regardless of
number of wheels, plus my fast wide-track tadpole) are the
unnecessary
jewelry of an excessive society.
Copyright 2009 Andre Jute
Free to use on not-for-profit netsites as longs the entire article,
including this notice, is reprinted intact. Any other use contact
author

  #10  
Old June 3rd 09, 09:07 PM posted to rec.bicycles.tech,alt.rec.bicycles.recumbent
Antitroll
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Posts: 52
Default THE LOGIC OF TRIKES an outsider's viewpoint by Andre Jute


"Andre Jute" wrote in message
...
among a whole lot of guff
" I didn't become interested in
lightweight construction (meaning for road use, outside racing, lest
some idiot publishes an old photo of me working on a racing frame and
calls me a liar) until I had already given up the car to become a
cyclist
Andre Jute"

There ARE no old photos of you working on a racing frame nor any independent
proof, either photographic or textual that you have ever designed or built any
vehicle with any number of wheels.
PH


 




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