Kit 2 convert front of upright bike to 2 wheels?

Frank Krygowski wrote:
On 4/20/2015 1:35 PM, Jeff Liebermann wrote:
On Mon, 20 Apr 2015 10:52:09 -0400, Frank Krygowski
wrote:

I'm pretty sure that a trike with two front wheels (i.e. a tadpole
trike) is much more stable than a single front wheel trike (i.e. a delta
trike). The big difference comes when a person "overcooks a turn,"
entering it too fast. The natural response is to brake, which (in
common parlance) throws the rider's weight forward and toward the
outside of the turn. A tadpole trike has a front wheel in a position to
resist the resultant tipping; a delta trike does not.

On thinking it over again, I have to admit that you're correct.

I happen to be currently looking for a tricycle or tricycle conversion
for a friend who has balance problems. Stability is a major concern
so I did some test rides on prospective used bicycles to see how they
feel. I haven't ridden a tricycle for many years and had no idea how
it would ride. I certainly had problems in a turn, especially on
non-level ground as you describe and agree that reversing the wheel
arrangement would help. This also agrees with the conventional
wisdom:
http://auto.howstuffworks.com/three-wheel-car4.htm
It's probably similar to blowing a tire on a automobile. If I lose a
rear tire, the car will skid somewhat. If the engine is still
running, some control can be maintained using the front wheels.
However, if a front tire blows, the car will turn in the direction of
the blown tire, and possibly roll by tripping over the blown tire.

However, I'm worried about how a tadpole arrangement would work on a
downhill run. With most of the weight towards the front, I suspect
that it might cause both wheels to swing in the direction of the turn,
and then pitch pole forward. The area where we live doesn't have any
flat terrain. The only way I can be sure is to try it. I don't have
such a machine, so this is only a guess(tm).

Also, I'm worried about what a tadpole arrangement might do without
the articulated arrangement, where one wheel might lift off the
ground. Again, I would need to try it.

Regarding the kinematic nightmare in the triblean, my guess is that it's
needed only to allow leaning into the curve. That's probably necessary
for sporting riding, but perhaps not for slow puttering.

Agreed, although I think the kinematic nightmare might have steering
and control benefits by keeping all 3 wheels on the ground on rough
and uneven roads.

I doubt it has
anything to do with handlebar reaction torques, which is what I think
you're describing with "handlebars turn inward."

Yep. Part of stability is control. It's difficult to tell from the
photos, but it looks like the equivalent of the head tube angle might
be more vertical than the usual 65 to 75 degrees:
http://www.core77.com/posts/18082/triblean-retrofit-kit-makes-tricycles-for-grown-ups-18082
With no hands on the handlebars, my guess(tm) is that it won't go in a
straight line. However, with the different turning radii of the two
front wheels, I don't have a clue what it might do in a sharp turn.

I'd think that aspect
could be controlled by the proper choice of steering trail and other
geometry.

Certainly. A very relaxed 65 degree head tube angle and large front
fork offset (rake) would certainly help. However, too much of these
will make the machine difficult to turn, with the turning resistance
being twice that of a conventional 2 wheel bicycle because one has to
turn two wheels.

Anybody got a link to the details of the tilting front suspension as
used on things like Piaggio scooters? Those seem to work quite well,
although I've never had a chance to test one.

Not me, but there might be something on 3 wheel motorcycle
conversions.

As long as we're discussing these things, another disadvantage to 3
wheelers is the need to find not one, not two, but three separate and
properly spaced smooth tracks between the potholes. With the record crop
of potholes in our area, that's no small task.

On a club ride last week, a new guy came along riding his super-low
recumbent trike. It did fine on smooth roads, particularly if they were
downhill. But on one potholey downhill, he screeched to a stop to
recover a taillight that had knocked loose when he couldn't avoid some bad bumps.

We've got enough potholes that finding one track through, for a
two-wheeler, is sometimes an impossible task. And if that situation
occurs, I can at least stand up, and perhaps jump the bike over a hole.
He had no such defense.

But I can certainly see an upright trike making sense for a person with
balance problems. Heck, I may be in that situation myself, some day.

I rode through an area we dubbed "bird**** alley" along with my buddy on
his trike. It was definitely easier for me to avoid the "jewels" on the
pavement. What's worse was that I had fenders and he didn't.

Jeff Liebermann wrote:
On Mon, 20 Apr 2015 10:52:09 -0400, Frank Krygowski
wrote:

I'm pretty sure that a trike with two front wheels (i.e. a tadpole
trike) is much more stable than a single front wheel trike (i.e. a delta
trike). The big difference comes when a person "overcooks a turn,"
entering it too fast. The natural response is to brake, which (in
common parlance) throws the rider's weight forward and toward the
outside of the turn. A tadpole trike has a front wheel in a position to
resist the resultant tipping; a delta trike does not.

On thinking it over again, I have to admit that you're correct.

I happen to be currently looking for a tricycle or tricycle conversion
for a friend who has balance problems. Stability is a major concern
so I did some test rides on prospective used bicycles to see how they
feel. I haven't ridden a tricycle for many years and had no idea how
it would ride. I certainly had problems in a turn, especially on
non-level ground as you describe and agree that reversing the wheel
arrangement would help. This also agrees with the conventional
wisdom:
http://auto.howstuffworks.com/three-wheel-car4.htm
It's probably similar to blowing a tire on a automobile. If I lose a
rear tire, the car will skid somewhat. If the engine is still
running, some control can be maintained using the front wheels.
However, if a front tire blows, the car will turn in the direction of
the blown tire, and possibly roll by tripping over the blown tire.

However, I'm worried about how a tadpole arrangement would work on a
downhill run. With most of the weight towards the front, I suspect
that it might cause both wheels to swing in the direction of the turn,
and then pitch pole forward. The area where we live doesn't have any
flat terrain. The only way I can be sure is to try it. I don't have
such a machine, so this is only a guess(tm).

Also, I'm worried about what a tadpole arrangement might do without
the articulated arrangement, where one wheel might lift off the
ground. Again, I would need to try it.

Regarding the kinematic nightmare in the triblean, my guess is that it's
needed only to allow leaning into the curve. That's probably necessary
for sporting riding, but perhaps not for slow puttering.

Agreed, although I think the kinematic nightmare might have steering
and control benefits by keeping all 3 wheels on the ground on rough
and uneven roads.

I doubt it has
anything to do with handlebar reaction torques, which is what I think
you're describing with "handlebars turn inward."

Yep. Part of stability is control. It's difficult to tell from the
photos, but it looks like the equivalent of the head tube angle might
be more vertical than the usual 65 to 75 degrees:
http://www.core77.com/posts/18082/triblean-retrofit-kit-makes-tricycles-for-grown-ups-18082
With no hands on the handlebars, my guess(tm) is that it won't go in a
straight line. However, with the different turning radii of the two
front wheels, I don't have a clue what it might do in a sharp turn.

I'd think that aspect
could be controlled by the proper choice of steering trail and other
geometry.

Certainly. A very relaxed 65 degree head tube angle and large front
fork offset (rake) would certainly help. However, too much of these
will make the machine difficult to turn, with the turning resistance
being twice that of a conventional 2 wheel bicycle because one has to
turn two wheels.

Anybody got a link to the details of the tilting front suspension as
used on things like Piaggio scooters? Those seem to work quite well,
although I've never had a chance to test one.

Not me, but there might be something on 3 wheel motorcycle
conversions.




If you want stability on a trike, you gotta get low. My buddy has a Catrike
and unless he's seriously cooking in a corner, all the wheels stay on the
pavement.

On 4/20/2015 10:57 PM, Ralph Barone wrote:
J

If you want stability on a trike, you gotta get low. My buddy has a Catrike
and unless he's seriously cooking in a corner, all the wheels stay on the
pavement.

Supposedly, one of Catrike's biggest dealers is about 30 miles from
here, very close to the snack stop for our club's spring invitational
ride. It's close to a very nice MUP that we use for that ride.

At that snack stop, I've seen Catrike riders show off by sliding
sideways as they whipped to a stop in the parking lot.

However, I don't think many of those folks venture off the path with
their trikes. Personally, I wouldn't like mixing it up with traffic
while being so low.

--
- Frank Krygowski

Frank Krygowski wrote:
On 4/20/2015 10:57 PM, Ralph Barone wrote:
J

If you want stability on a trike, you gotta get low. My buddy has a Catrike
and unless he's seriously cooking in a corner, all the wheels stay on the
pavement.

Supposedly, one of Catrike's biggest dealers is about 30 miles from here,
very close to the snack stop for our club's spring invitational ride.
It's close to a very nice MUP that we use for that ride.

At that snack stop, I've seen Catrike riders show off by sliding sideways
as they whipped to a stop in the parking lot.

However, I don't think many of those folks venture off the path with
their trikes. Personally, I wouldn't like mixing it up with traffic while being so low.


My buddy with the Catrike says that he was in a parking lot once, when
somebody didn't see him and almost drive into him. After he tells the
story, he adds that he was driving his motor home at the time. If
somebody's not going to see you, it may not matter what you're riding.
Besides, that's what the flippy flag is for.

On 4/20/2015 6:02 PM, James wrote:
On 21/04/15 03:35, Jeff Liebermann wrote:
On Mon, 20 Apr 2015 10:52:09 -0400, Frank Krygowski
wrote:


I'd think that aspect
could be controlled by the proper choice of steering trail and other
geometry.

Certainly. A very relaxed 65 degree head tube angle and large front
fork offset (rake) would certainly help. However, too much of these
will make the machine difficult to turn, with the turning resistance
being twice that of a conventional 2 wheel bicycle because one has to
turn two wheels.


ISTM, more rake reduces trail and in fact makes for a less stable
steering geometry. Forks with less rake increases trail because they
put the contact patch further behind the steering axis, rather than
closer to it. There is a small range of trail that, from what I
understand, can provide everything from slow and stable steering to
twitchy and a feeling of instability. Beyond this range may produce
undesirable handling for anyone.

http://www.bikeforums.net/framebuild...-handling.html

From what I understand, this is one of those problems for which
mathematics doesn't yet provide a clean solution. The rules of thumb
that exist seem to have been developed almost entirely by trial and
error, or Darwinian mechanical design. Or perhaps art vs. science.

Fred DeLong's 1974 book _DeLong's Guide to Bicycles and Bicycling_ has a
couple pages discussing stability and its relation to head angle and
fork offset or to trail. One formula that he gives for "satisfactory
steering" is called the Davidson formula:
fork offset = wheel radius * tan((90 degrees - head tube angle)/2)

He also has a graph evaluating "stability index" by other means. I once
evaluated a bunch of bike specs against this graph. They came out with
widely varying "stability indexes" even among bikes of the same general
type (i.e. among racing bikes, or among touring bikes).

DeLong had a fork built with dropouts that allowed adjustable trail,
which he used to evaluate handling under different conditions, which he
rated on a vague scale "poor, fair, good, excellent." He plotted four
different curves, for 1) high speed riding, 2) gravel roads, 3)
hands-off riding and 4) "snaking." According to him, the best handling
for each of those occurred with different amounts of trail.

David Gordon Wilson's _Bicycling Science_ has a chapter on steering and
balancing written by Jim Papadopoulos, who probably knows more about
this than any other human being. It's wonderfully arcane, and it ends
with a confession by Wilson that there's obviously a lot more to this issue.

--
- Frank Krygowski

Frank Krygowski writes:

On 4/20/2015 6:02 PM, James wrote:
On 21/04/15 03:35, Jeff Liebermann wrote:
On Mon, 20 Apr 2015 10:52:09 -0400, Frank Krygowski
wrote:


I'd think that aspect
could be controlled by the proper choice of steering trail and other
geometry.

Certainly. A very relaxed 65 degree head tube angle and large front
fork offset (rake) would certainly help. However, too much of these
will make the machine difficult to turn, with the turning resistance
being twice that of a conventional 2 wheel bicycle because one has to
turn two wheels.


ISTM, more rake reduces trail and in fact makes for a less stable
steering geometry. Forks with less rake increases trail because they
put the contact patch further behind the steering axis, rather than
closer to it. There is a small range of trail that, from what I
understand, can provide everything from slow and stable steering to
twitchy and a feeling of instability. Beyond this range may produce
undesirable handling for anyone.

http://www.bikeforums.net/framebuild...-handling.html

From what I understand, this is one of those problems for which
mathematics doesn't yet provide a clean solution. The rules of thumb
that exist seem to have been developed almost entirely by trial and
error, or Darwinian mechanical design. Or perhaps art vs. science.

Fred DeLong's 1974 book _DeLong's Guide to Bicycles and Bicycling_ has
a couple pages discussing stability and its relation to head angle and
fork offset or to trail. One formula that he gives for "satisfactory
steering" is called the Davidson formula:
fork offset = wheel radius * tan((90 degrees - head tube angle)/2)

He also has a graph evaluating "stability index" by other means. I
once evaluated a bunch of bike specs against this graph. They came
out with widely varying "stability indexes" even among bikes of the
same general type (i.e. among racing bikes, or among touring bikes).

DeLong had a fork built with dropouts that allowed adjustable trail,
which he used to evaluate handling under different conditions, which
he rated on a vague scale "poor, fair, good, excellent." He plotted
four different curves, for 1) high speed riding, 2) gravel roads, 3)
hands-off riding and 4) "snaking." According to him, the best
handling for each of those occurred with different amounts of trail.

David Gordon Wilson's _Bicycling Science_ has a chapter on steering
and balancing written by Jim Papadopoulos, who probably knows more
about this than any other human being. It's wonderfully arcane, and
it ends with a confession by Wilson that there's obviously a lot more
to this issue.

I believe Jim Papadoupolous has more or less solved the problem in
the last few years; I've got the paper around here somewhere.

--
Joe Riel

Am 21.04.2015 um 05:41 schrieb Frank Krygowski:

However, I don't think many of those folks venture off the path with
their trikes. Personally, I wouldn't like mixing it up with traffic
while being so low.

I commuted on my tadpole recumbent rike for several years. The only
situation where I felt a flag was useful was on an uphill section ( 10
mph) with several lanes suddenly splitting into different directions.
When I was in the right lane due to speed and a car behind me did not
want to overtake shortly before turning right, I was afraid that a
second car would overtake the first car and then pull right into exactly
where I was.

Am 20.04.2015 um 01:46 schrieb Sir Ridesalot:
I know there's a kit to convert the rear of an upright bike to two
wheels and wonder if there's one to convert the front to two wheels
as the two front wheels trikes are said to be a lot more stable than
the two rear wheels trikes are. Anyone know of a two wheels front
conversion?

What's your motivation to convert a bike to a trike? The most common
motivation is to enable riding for somebody who lacks the motor skill to
control the leaning of a normal bike (e.g. after a stroke).

Non-leaning tadpole trikes are stable on two conditions:
1) Ackermann steering
2) low center of gravity

It is completely impossible to reach number 2 on a bike conversion kit.
It is also extremely challenging to think of a steering mechanism that
works on an upright tadpole trike.

On 21/04/15 14:45, Joe Riel wrote:


I believe Jim Papadoupolous has more or less solved the problem in
the last few years; I've got the paper around here somewhere.


IIRC his is about bicycles that are "self stable" when in motion and
without a rider. Is that useful?

--
JS

On 4/21/2015 3:49 AM, James wrote:
On 21/04/15 14:45, Joe Riel wrote:


I believe Jim Papadoupolous has more or less solved the problem in
the last few years; I've got the paper around here somewhere.


IIRC his is about bicycles that are "self stable" when in motion and
without a rider. Is that useful?

Jim Papadoupolous is pretty clear about the (current) limitations of his
work. He's been working mostly on self-stability, but he says
"self-stability is not the same as nice handling qualities."

There's good discussion at
https://janheine.wordpress.com/2011/...orks-together/

--
- Frank Krygowski