???Long wheelbase + Balloon tyres + Underinflation = Understeer???

My Utopia Kranich has a looong wheelbase of 1149mm and balloon tyres,
which I keep inflated to the a minimum level that avoids snakebite
punctures. In theory this is a recipe that mathematically we might
express as:

???Long wheelbase + Balloon tyres + Underinflation = Understeer???

The question is of course, How much understeer? When does it become
unpleasant or even dangerous?

In everyday use I don't notice the wheelbase or the response. I don't
expect a bike this big to respond in the same way as one with a
wheelbase 130mm, over five inches, shorter, like my Trek L700 Smover
or even my Gazelle Toulouse, both of which run on 70psi 37mm Marathon
Plus (or direct Bontrager equivalent) whereas the Kranich runs on 60mm
Big Apple Liteskins inflated to a maximum of 29psi (2 bar), usually
less. In fact, I was pleasantly surprised by the roadholding of the
Kranich, which in is quite as good as the smaller bikes on the
Marathon Plus.

Handling is what happens when you run out of roadholding.

Yesterday I had a couple of incidents which made me pay attention to
the roadholding for the first time since a monster moment last year on
a rainwet downhill road further slippery with slurry (liquid cowdung)
and with a tractor parked across the entire road before me in the
dark, which I survived by crashing into the tractor tyre rather than
some harder part of it.

Yesterday. First, at a junction where oncoming, turning traffic is
supposed to give way to traffic from the side I was on, a woman in a
small car turned, decided she wouldn't make it, and stopped dead
across a narrow road, sliding to a stop and stalling her car. I could
go into her or around the wrong side. I went around the wrong side,
then, almost clear, damned nearly lost the front wheel on loose
gravel.

Next, perhaps riding a bit exuberantly in clear lanes because it was
the first good ride after the winter, I damn nearly lost it again on
loose gravel road menders left on a corner at which I normally take
more care simply because the corner is blind and the road narrow and
the ditch both deep and overgrown by gorse with vicious thorns.

The lanes on which I ride are narrow. The tarmac on each side drops
off five inches minimum, straight down onto mud, sometimes straight
into the ditch. You go off the edge at an acute angle, you *will*
fall, back onto the road against or under the wheels of the car that
pushed you off. On both occasions, on a recovered bike, I went further
towards the dropoff than was comfortable or safe. On both occasions I
had an opportunity to observe how slowly a long wheelbase bike fitted
with low-pressure balloons responds.

Of course, when I drove a Bentley, I sometimes wished it would respond
like the Porsche I drove before, but then I remembered the reptilian
writhing of the Porsche steering wheel, and the noise, and the
cramped, ugly interior, and just drove a fraction slower to return to
the comfort band of its very high level of roadholding. In the end,
I'd arrive as fast in the Bentley, and relaxed, and my passengers
wouldn't even know it had been a heroic journey, whereas Porsche
passengers climbed out all tense.

The same with the Kranich. Within its limits it is a fast, powerful
bike, above all the ultimate comfort bike, very versatile, sweeping
along at amazing speed on twisting country lanes. It doesn't demand
much of the rider until some very high limit is reached. But when it
has nothing more to give, the rider had better be pretty skilled,
because it won't get out of trouble with that twitch of the handlebars
that saves a roadie on his 15 pound bike in the same circumstances.

Mind you, on the other hand it won't let that twitch cause a crash
either, as is equally likely on a road bike. At any speed, sane or
insane, it takes some really special effort to tip over a bike on the
60mm Big Apples.

Andre Jute
A man should know his limits. -- Dirty Harry Callahan

On Mar 25, 11:57*am, Andre Jute wrote:
My Utopia Kranich has a looong wheelbase of 1149mm and balloon tyres,
which I keep inflated to the a minimum level that avoids snakebite
punctures. In theory this is a recipe that mathematically we might
express as:

???Long wheelbase + Balloon tyres + Underinflation = Understeer???

The question is of course, How much understeer? When does it become
unpleasant or even dangerous?

In everyday use I don't notice the wheelbase or the response. I don't
expect a bike this big to respond in the same way as one with a
wheelbase 130mm, over five inches, shorter, like my Trek L700 Smover
or even my Gazelle Toulouse, both of which run on 70psi 37mm Marathon
Plus (or direct Bontrager equivalent) whereas the Kranich runs on 60mm
Big Apple Liteskins inflated to a maximum of 29psi (2 bar), usually
less. In fact, I was pleasantly surprised by the roadholding of the
Kranich, which in is quite as good as the smaller bikes on the
Marathon Plus.

Handling is what happens when you run out of roadholding.

Yesterday I had a couple of incidents which made me pay attention to
the roadholding for the first time since a monster moment last year on
a rainwet downhill road further slippery with slurry (liquid cowdung)
and with a tractor parked across the entire road before me in the
dark, which I survived by crashing into the tractor tyre rather than
some harder part of it.

Yesterday. First, at a junction where oncoming, turning traffic is
supposed to give way to traffic from the side I was on, a woman in a
small car turned, decided she wouldn't make it, and stopped dead
across a narrow road, sliding to a stop and stalling her car. I could
go into her or around the wrong side. I went around the wrong side,
then, almost clear, damned nearly lost the front wheel on loose
gravel.

Next, perhaps riding a bit exuberantly in clear lanes because it was
the first good ride after the winter, I damn nearly lost it again on
loose gravel road menders left on a corner at which I normally take
more care simply because the corner is blind and the road narrow and
the ditch both deep and overgrown by gorse with vicious thorns.

The lanes on which I ride are narrow. The tarmac on each side drops
off five inches minimum, straight down onto mud, sometimes straight
into the ditch. You go off the edge at an acute angle, you *will*
fall, back onto the road against or under the wheels of the car that
pushed you off. On both occasions, on a recovered bike, I went further
towards the dropoff than was comfortable or safe. On both occasions I
had an opportunity to observe how slowly a long wheelbase bike fitted
with low-pressure balloons responds.

Of course, when I drove a Bentley, I sometimes wished it would respond
like the Porsche I drove before, but then I remembered the reptilian
writhing of the Porsche steering wheel, and the noise, and the
cramped, ugly interior, and just drove a fraction slower to return to
the comfort band of its very high level of roadholding. In the end,
I'd arrive as fast in the Bentley, and relaxed, and my passengers
wouldn't even know it had been a heroic journey, whereas Porsche
passengers climbed out all tense.

The same with the Kranich. Within its limits it is a fast, powerful
bike, above all the ultimate comfort bike, very versatile, sweeping
along at amazing speed on twisting country lanes. It doesn't demand
much of the rider until some very high limit is reached. But when it
has nothing more to give, the rider had better be pretty skilled,
because it won't get out of trouble with that twitch of the handlebars
that saves a roadie on his 15 pound bike in the same circumstances.

Mind you, on the other hand it won't let that twitch cause a crash
either, as is equally likely on a road bike. At any speed, sane or
insane, it takes some really special effort to tip over a bike on the
60mm Big Apples.

Andre Jute
A man should know his limits. -- Dirty Harry Callahan

The long wheel base results in a more balanced load between tires. In
a short wheelbase diamond frame, as much as 80% of the weight is in
the rear. But a LWB recumbent will be much closer to a 50% split, so
turning will increase the friction requirements in front resulting in
easier front tire skids.

Second, loose debris accumulated on the side over the winter months,
and is not well packed. In a couple of months, the gravel and other
items on the side will be removed or compacted and will not skid as
fast.

On 3/25/2011 3:09 PM, wrote:
On Mar 25, 11:57 am, Andre wrote:
My Utopia Kranich has a looong wheelbase of 1149mm and balloon tyres,
which I keep inflated to the a minimum level that avoids snakebite
punctures. In theory this is a recipe that mathematically we might
express as:

???Long wheelbase + Balloon tyres + Underinflation = Understeer???

The question is of course, How much understeer? When does it become
unpleasant or even dangerous?
.....

The problem of running fat tires at low pressure on narrow rims is that
the tires tend to fold over sideways around turns--particularly the
front tire.

If you want to run wide tires, you also need wide rims. Not just "a
little bit" wider, not 2mm or 3mm. Go get rims as wide as, or only
slightly narrower than the tire itself.

In every other kind of wheeled-vehicle racing it is recognized that
wider tires demand wider rims. It is only among bicyclists that this
matter gets ignored--where you will see the fattest tires mounted on
some of the most-narrow rims.


The long wheel base results in a more balanced load between tires. In
a short wheelbase diamond frame, as much as 80% of the weight is in
the rear. But a LWB recumbent will be much closer to a 50% split, so
turning will increase the friction requirements in front resulting in
easier front tire skids.


I would think that among upright bikes, the general design is so similar
from one model to another that any differences in weight distribution
would be tiny, varying less than /maybe/ 5% among all models.

Upright bikes are pretty good at providing near-50-50 weight
distribution, but weather that's a useful aspect for a bicycle is
another question entirely. My own thoughts are that (for most riders) it
is not, for a couple of reasons. First is motive efficiency of the
rear-wheel-drive setup: dragsters try to place as much of their weight
over the rear wheels for the reason that it works better that way.
Second is the ability to make harder sudden stops without tipping over
forward (a problem of the previously-popular penny-farthings that safety
bicycles were supposed to solve).

I don't see how it would be possible to build a bicycle frame that
provided a significant rearward weight distribution, and still have it
look like a normal bicycle. Beyond a certain point you can't tilt the
head tube angle further, so you would end up with a remote steering
setup like what's on the Bakfiets cargo bikes.

------

As for LWB recumbents, I assure you probably none manage to get a 50-50
weight distribution, my own is observed to be more like 33%F-66%R. Since
most of your weight is in your torso, only a big-sized LWB with a very
small rider would come close to 50-50. Some of the short-wheelbase bikes
hit very close to 50-50 with a normal-sized rider, if you feel it's
worthwhile.

yeah. You were waxy abt Schwalbe's Apples. Gotta use wide rims.
Inflation won;t cure the flop over.

but discussion of over and under-when the front slides of the turn to
the outside first-lika 429 Mustang-that's understeer. But people will
focus on the light rear end and say its oversteer and itsnot.

VW Beetles oversteer in snow and rain, Porsches oversteer if you let
off the throttle

FWD tend to overundersteer if the throttle is backed off turning close
to the limit...lottsa people die caws of it. They don't know how to
drive FWD. DUI Hi speed lane changes then back offs at the end of the
manuver and whooops right into the opposite lane.

great fun in the snow...spins right around 360 while travleing 180

"I don't see how it would be possible to build a bicycle frame that
provided a significant rearward weight distribution, and still have
it
look like a normal bicycle" GOOD GRIEF ! call Fisher...

if yawl countersteer and use wide rims then the prob feel will go
away. lile certainly the designer did not want that effect. he was
looking for balance in countersteer and less so

Per DougC:
The problem of running fat tires at low pressure on narrow rims is that
the tires tend to fold over sideways around turns--particularly the
front tire.

And, at higher pressures, given a sufficiently too-narrow rim,
they'll just blow off the rim. Been there, done that.
--
PeteCresswell

On Mar 25, 8:09*pm, "
wrote:
On Mar 25, 11:57*am, Andre Jute wrote:





My Utopia Kranich has a looong wheelbase of 1149mm and balloon tyres,
which I keep inflated to the a minimum level that avoids snakebite
punctures. In theory this is a recipe that mathematically we might
express as:

???Long wheelbase + Balloon tyres + Underinflation = Understeer???

The question is of course, How much understeer? When does it become
unpleasant or even dangerous?

In everyday use I don't notice the wheelbase or the response. I don't
expect a bike this big to respond in the same way as one with a
wheelbase 130mm, over five inches, shorter, like my Trek L700 Smover
or even my Gazelle Toulouse, both of which run on 70psi 37mm Marathon
Plus (or direct Bontrager equivalent) whereas the Kranich runs on 60mm
Big Apple Liteskins inflated to a maximum of 29psi (2 bar), usually
less. In fact, I was pleasantly surprised by the roadholding of the
Kranich, which in is quite as good as the smaller bikes on the
Marathon Plus.

Handling is what happens when you run out of roadholding.

Yesterday I had a couple of incidents which made me pay attention to
the roadholding for the first time since a monster moment last year on
a rainwet downhill road further slippery with slurry (liquid cowdung)
and with a tractor parked across the entire road before me in the
dark, which I survived by crashing into the tractor tyre rather than
some harder part of it.

Yesterday. First, at a junction where oncoming, turning traffic is
supposed to give way to traffic from the side I was on, a woman in a
small car turned, decided she wouldn't make it, and stopped dead
across a narrow road, sliding to a stop and stalling her car. I could
go into her or around the wrong side. I went around the wrong side,
then, almost clear, damned nearly lost the front wheel on loose
gravel.

Next, perhaps riding a bit exuberantly in clear lanes because it was
the first good ride after the winter, I damn nearly lost it again on
loose gravel road menders left on a corner at which I normally take
more care simply because the corner is blind and the road narrow and
the ditch both deep and overgrown by gorse with vicious thorns.

The lanes on which I ride are narrow. The tarmac on each side drops
off five inches minimum, straight down onto mud, sometimes straight
into the ditch. You go off the edge at an acute angle, you *will*
fall, back onto the road against or under the wheels of the car that
pushed you off. On both occasions, on a recovered bike, I went further
towards the dropoff than was comfortable or safe. On both occasions I
had an opportunity to observe how slowly a long wheelbase bike fitted
with low-pressure balloons responds.

Of course, when I drove a Bentley, I sometimes wished it would respond
like the Porsche I drove before, but then I remembered the reptilian
writhing of the Porsche steering wheel, and the noise, and the
cramped, ugly interior, and just drove a fraction slower to return to
the comfort band of its very high level of roadholding. In the end,
I'd arrive as fast in the Bentley, and relaxed, and my passengers
wouldn't even know it had been a heroic journey, whereas Porsche
passengers climbed out all tense.

The same with the Kranich. Within its limits it is a fast, powerful
bike, above all the ultimate comfort bike, very versatile, sweeping
along at amazing speed on twisting country lanes. It doesn't demand
much of the rider until some very high limit is reached. But when it
has nothing more to give, the rider had better be pretty skilled,
because it won't get out of trouble with that twitch of the handlebars
that saves a roadie on his 15 pound bike in the same circumstances.

Mind you, on the other hand it won't let that twitch cause a crash
either, as is equally likely on a road bike. At any speed, sane or
insane, it takes some really special effort to tip over a bike on the
60mm Big Apples.

Andre Jute
A man should know his limits. -- Dirty Harry Callahan

The long wheel base results in a more balanced load between tires. *In
a short wheelbase diamond frame, as much as 80% of the weight is in
the rear. *But a LWB recumbent will be much closer to a 50% split, so
turning will increase the friction requirements in front resulting in
easier front tire skids.

Second, loose debris accumulated on the side over the winter months,
and is not well packed. *In a couple of months, the gravel and other
items on the side will be removed or compacted and will not skid as
fast.

Yeah, this looks like overexuberance at the beginning of spring and
adverse circumstances at the end of winter meeting each other. But I
wasn't really concentrating on the two slides and near front wipe-
outs. I've put up my hand for those already. They were expected under
the circumstances.

My interest is in the recovery afterwards, the handling of the bike
after the rider runs out of roadholding.

On giving it some thought with a drink in my hand, I've concluded
that, were I on a road bike, I would probably have come a cropper by
trying to get out of trouble too fast, that the measure of understeer
resulting from a long wheelbase, fat low pressure tyres and more
rearward weight distribution (that one is counterintuitive -- come
back soon, Jobst!), is indeed a contribution to the general safety of
conducting the bike at quite inordinate speeds.

Andre Jute
Suspended by Schwalbe

On Mar 25, 10:02*pm, DougC wrote:
On 3/25/2011 3:09 PM, wrote:

On Mar 25, 11:57 am, Andre *wrote:
My Utopia Kranich has a looong wheelbase of 1149mm and balloon tyres,
which I keep inflated to the a minimum level that avoids snakebite
punctures. In theory this is a recipe that mathematically we might
express as:

???Long wheelbase + Balloon tyres + Underinflation = Understeer???

The question is of course, How much understeer? When does it become
unpleasant or even dangerous?
.....

The problem of running fat tires at low pressure on narrow rims is that
the tires tend to fold over sideways around turns--particularly the
front tire.

Doug, I don't know where you get the idea I would do anything as
stupid as to run fat tyres on narrow rims. I ride on custom designed
and made rims approved as more than adequately wide for the 60mm Big
Apples by Schwalbe, by the rim maker, by the bike manufacturer, by
their independent tester, by the industry body, by the German
government.

I conducted test when I got the bike, complete with a spare set of
tyres because I expected to destroy one pair of tyres in these tests,
to see if I could make the tyre fold over or blow off the rim. I
couldn't. Nor were the tyres destroyed; just a little scuffed from
where I ran out of road a few times.

On Mar 26, 12:55*am, "(PeteCresswell)" wrote:
Per DougC:

The problem of running fat tires at low pressure on narrow rims is that
the tires tend to fold over sideways around turns--particularly the
front tire.

And, at higher pressures, given a sufficiently too-narrow rim,
they'll just blow off the rim. * Been there, done that.
--
PeteCresswell

You should have taken advice from Chalo. I did, and am eminently
satisfied I got the right gen. I conducted tests with 17mm, 19mm and
25mm rims wearing 60mm Big Apples. The 17mm was unsatisfactory but you
really had to ride the bike on the wrong side of reckless to discover
this, and the lack of satisfaction was nowhere near a tyre deforming
to the extent of folding over or blowing off the rim, it was the
comfort that was kibbitzed because the tyres had to be pumped to 38psi
to avoid snakebites when riding over kerbs. The 19mm was surprisingly
good in any kind of use short of suicidal; where you miss out is in
comfort because you have to inflate a fraction more than on wider
rims. I suspect that, if you blew Big Apples off the rim, you were
using a really grossly unsuitable rim, or seriously overinflating. A
25mm rim is satisfactory in all respects. I suspect anyone who took
Doug's advice and bought a rim 60mm wide to fit a 60mm low-pressure
tyre/combo would soon be so frustated by his rim being destroyed by
the road through being to close to it, that he would give up cycling.
The pure height of a Big Apple is a security zone on rough roads.

On Mar 25, 11:45*pm, kolldata wrote:
yeah. You were waxy abt Schwalbe's Apples. Gotta use wide rims.
Inflation won;t cure the flop over.

I'm still waxy about Schwalbe's Big Apples. I have wide rims. My tyres
don't flop over. I have no intention of increasing the pressure in
them.

I was really just making a description of an event where my own excess
gave me an opportunity to investigate the limits of roadholding of the
Big Apples, and to admire their calm handling of two events in short
which could both have turned nasty, and on a twitchy bike on high-
pressure tyres probably would have turned nasty.

Those Big Apples saved my ass, twice on one day, so why should I want
to mess with anything about them? You guys just aren't making sense.

Thanks for the rest of the car stuff. I wrote a book about it about
thirty years ago.

On 3/25/2011 5:02 PM, Doug Cimper wrote:
On 3/25/2011 3:09 PM, wrote:
[...]
The long wheel base results in a more balanced load between tires. In
a short wheelbase diamond frame, as much as 80% of the weight is in
the rear. But a LWB recumbent will be much closer to a 50% split, so
turning will increase the friction requirements in front resulting in
easier front tire skids.

[...]
As for LWB recumbents, I assure you probably none manage to get a 50-50
weight distribution, my own is observed to be more like 33%F-66%R. Since
most of your weight is in your torso, only a big-sized LWB with a very
small rider would come close to 50-50. Some of the short-wheelbase bikes
hit very close to 50-50 with a normal-sized rider, if you feel it's
worthwhile.

My LWB RANS Tailwind has the weight far enough to the rear that I can do
"power wheelies" when starting out. I also have had the front wheel
lift slightly when climbing steep hills on my SWB RANS Rocket (a lower
gear for smoother spinning would help here).

--
Tºm Shermªn - 42.435731,-83.985007
I am a vehicular cyclist.