Fixed gear/track frame geometry

James Thomson said:

Benjamin Lewis said:

The best analysis I've found so far is the paper by
David E. H. Jones, "The Stability of the Bicycle", where
he attempts to build several "unrideable bicycles"
(URBs). It's much more rambling and casual than a
typical academic paper, but I found it somewhat
enjoyable to read.

Have you seen the papers linked from:

tam.cornell.edubicycles.htmlOpen ↗

particularly Scott Hand's thesis, and Jim Papadopoulos'
summary of it?

No, I haven't. Thanks for the link, looks like it might be
just what I was looking for.

--
Benjamin Lewis

Hey! I'm only fourteen, sickly 'n' thin Tried all of my life
just to grow me a chin It popped out once, but my dad pushed
it in. -- FZ

LOL. "[D]ead wrong" and "unhelpful" and putting words in the
mouth of JF. LOL

Your criticism is of the value of 'very' since every other
statement in the context is exactly truthful and still you
find it "unhelpful". And excuse your density with 'I suspect
the author is confused'!

You are an undergraduate? or wish your work 'reviewed' to a
similar standard thirty-ish years later? So much for 'peer
review'. Or are you a peer?

Perhaps Professor Patterson from Cal Poly, San Luis Obispo
and author of Lords of the Chain Ring might help. I believe
that he writes for under-grads.

"Benjamin Lewis" <[email hidden]> wrote in message news:yy7o1xkp1dog.fsf_-
[email hidden]...
||
| Hmm, some if not most of his description is dead wrong
| (e.g. "A bicycle with long trail is very sensitive and
| follows every lean you make"😉, and
at
| best I find the rest unhelpful.
|
| I suspect Forester is confused about the effect of fork
| offset (rake), and is under the common impression that
| increasing rake increases the trail, when in fact the
| opposite is true.
|
|

Doug Huffman said:

"Benjamin Lewis" <[email hidden]> wrote...

Quoted message said:

Quoted message said:

Hmm, some if not most of his description is dead wrong
(e.g. "A bicycle with long trail is very sensitive and
follows every lean you make"😉, and at best I find the
rest unhelpful.

I suspect Forester is confused about the effect of fork
offset (rake), and is under the common impression that
increasing rake increases the trail, when in fact the
opposite is true.

LOL. "[D]ead wrong" and "unhelpful" and putting words in
the mouth of JF. LOL

Your criticism is of the value of 'very' since every other
statement in the context is exactly truthful and still you
find it "unhelpful". And excuse your density with 'I
suspect the author is confused'!

No. My criticism is that Forester is claiming bicycles with
long trail have more sensitive steering, when exactly the
opposite is true.

--
Benjamin Lewis

Evelyn the dog, having undergone further modification,
pondered the significance of short-person behavior in pedal-
depressed panchromatic resonance and other highly ambient
domains... "Arf", she said.

Benjamin Lewis said:

Doug Huffman said:

"Benjamin Lewis" <[email hidden]> wrote...

Quoted message said:

Hmm, some if not most of his description is dead wrong
(e.g. "A bicycle with long trail is very sensitive and
follows every lean you make"😉, and at best I find the
rest unhelpful.

I suspect Forester is confused about the effect of fork
offset (rake), and is under the common impression that
increasing rake increases the trail, when in fact the
opposite is true.

LOL. "[D]ead wrong" and "unhelpful" and putting words in
the mouth of JF. LOL

Your criticism is of the value of 'very' since every other
statement in the context is exactly truthful and still you
find it "unhelpful". And excuse your density with 'I
suspect the author is confused'!

No. My criticism is that Forester is claiming bicycles
with long trail have more sensitive steering, when exactly
the opposite is true.

Only if you take the party line at face value. Longer trail
will help a bike track better but if you get inputs to the
steering outside of your control (wind, holes, bumps, ...)
longer trail will actually make your bike more sensitive.
It's a longer lever arm.

MOO, Matt

Quoted message said:

Benjamin Lewis said:

No. My criticism is that Forester is claiming bicycles
with long trail have more sensitive steering, when
exactly the opposite is true.

Only if you take the party line at face value.

I wasn't aware there was a "party line".

Quoted message said:

Longer trail will help a bike track better but if you get
inputs to the steering outside of your control (wind,
holes, bumps, ...) longer trail will actually make your
bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard to
holes and bumps. Do you have any citations to support this?
If steering does indeed have to do directly with length of
the lever arm, it seems to me that a bump will result in a
fixed lateral displacement, which for a longer lever arm
will result in a smaller change in steering angle.

--
Benjamin Lewis

Amoebit: Amoeba/rabbit cross; it can multiply and divide at
the same time.

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis said:

No. My criticism is that Forester is claiming bicycles
with long trail have more sensitive steering, when
exactly the opposite is true.

Only if you take the party line at face value.

I wasn't aware there was a "party line".

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

Quoted message said:

Quoted message said:

Longer trail will help a bike track better but if you get
inputs to the steering outside of your control (wind,
holes, bumps, ...) longer trail will actually make your
bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments. Let's
consider what happens when you push on the head tube of a
bike, holding the bars fixed. With zero trail there will be
no twisting of the head tube around the head tube axis
because the tire/road contact point is directly on the axis.
As you increase the trail & the actual contact point moves
away from the 0-trail contact point, the twisting forces
increase. Now how do you twist this in real life? A strong
wind puts a sideways force on the bike. This force doesn't
affect the rear (fixed) but the front of the bike can get
pushed sideways. If there was zero trail, the front wheel
would act fixed like the rear and the front wheel would
still be tracking the direction of travel. As trail
increases, any rotation of the fork translates into a larger
offset of the contact point and affects the direction of
travel of the bike. The more flexible the front triangle the
more affect this has on the bike. As far as holes, cracks,
etc my belief is that the shorter the trail the easier it is
for the rider to resist the change caused by the outside
influence. Again consider the differences from zero trail to
something larger.

MOO, Matt

Benjamin Lewis said:

Doug Huffman said:

"Benjamin Lewis" <[email hidden]> wrote...

Quoted message said:

>
Hmm, some if not most of his description is dead wrong
(e.g. "A bicycle with long trail is very sensitive and
follows every lean you make"😉, and at best I find the
rest unhelpful.

I suspect Forester is confused about the effect of fork
offset (rake), and is under the common impression that
increasing rake increases the trail, when in fact the
opposite is true.

LOL. "[D]ead wrong" and "unhelpful" and putting words in
the mouth of JF. LOL

Your criticism is of the value of 'very' since every
other statement in the context is exactly truthful and
still you find it "unhelpful". And excuse your density
with 'I suspect the author is confused'!

No. My criticism is that Forester is claiming bicycles
with long trail have more sensitive steering, when exactly
the opposite is true.

Mr. Forester does seem confused on some mechanical matters.
He should have stuck to his knitting.

Matt O.

Quoted message said:

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis wrote:

> No. My criticism is that Forester is claiming bicycles
> with long trail have more sensitive steering, when
> exactly the opposite is true.

Only if you take the party line at face value.

I wasn't aware there was a "party line".

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

You may doubt as much as you want, but I disagree with
many "commonly accepted facts". I'm still not sure what
the commonly accepted facts *are* when it comes to
steering geometry.

Quoted message said:

Quoted message said:

Quoted message said:

Longer trail will help a bike track better but if you
get inputs to the steering outside of your control
(wind, holes, bumps, ...) longer trail will actually
make your bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments. Let's
consider what happens when you push on the head tube of a
bike, holding the bars fixed. With zero trail there will
be no twisting of the head tube around the head tube axis
because the tire/road contact point is directly on the
axis. As you increase the trail & the actual contact point
moves away from the 0-trail contact point, the twisting
forces increase. Now how do you twist this in real life? A
strong wind puts a sideways force on the bike.

I currently have no strong opinions how wind factors into
this, which is why I said "at least with regard to holes and
bumps". I have only rarely experienced steering trouble due
to cross winds, and then only when the wind is strong enough
that I have to lean noticeably in order to stay upright. I
don't use disc wheels, or even "aero" wheels, which probably
would create different steering effects in the wind.

Quoted message said:

This force doesn't affect the rear (fixed) but the front
of the bike can get pushed sideways. If there was zero
trail, the front wheel would act fixed like the rear and
the front wheel would still be tracking the direction of
travel. As trail increases, any rotation of the fork
translates into a larger offset of the contact point and
affects the direction of travel of the bike.

What makes you think a larger offset of the contact point
affects direction of travel, and what do you think is the
nature of this effect?

On a vehicle that stays upright when it turns (car,
tricycle), it is the steering angle, not the contact offset,
that affects turning radius. Although bicycle dynamics are
clearly different, it seems unlikely to me that this would
be reversed.

Quoted message said:

The more flexible the front triangle the more affect this
has on the bike. As far as holes, cracks, etc my belief is
that the shorter the trail the easier it is for the rider
to resist the change caused by the outside influence.
Again consider the differences from zero trail to
something larger.

Would you then recommend long distance riders switch from
touring bikes to racing bikes?

--
Benjamin Lewis

I regret to say that we of the FBI are powerless to act in
cases of oral-genital intimacy, unless it has in some way
obstructed interstate commerce. -- J. Edgar Hoover

ML said:

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis wrote:

>No. My criticism is that Forester is claiming bicycles
>with long trail have more sensitive steering, when
>exactly the opposite is true.

Only if you take the party line at face value.

I wasn't aware there was a "party line".

There is a "party line" only to the people who want to
appear like they have superior and arcane knowledge. The
rest of us are just trying to separate myth and lore from
reality, and are usually happy to get real facts.

Quoted message said:

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

Which might just be why he's asking the questions and trying
to get reliable information.

Quoted message said:

Quoted message said:

Quoted message said:

Longer trail will help a bike track better but if you get
inputs to the steering outside of your control (wind,
holes, bumps, ...) longer trail will actually make your
bike more sensitive. It's a longer lever arm.

Quoted message said:

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments.

Your post is at least as inaccurate, but Benjamin at least
has the wits to be asking for information whereas you are
just pontificating.

Quoted message said:

Let's consider what happens when you push on the head tube
of a bike, holding the bars fixed. With zero trail there
will be no twisting of the head tube around the head tube
axis because the tire/road contact point is directly on
the axis.

This only works as you claim when the steering axis is
normal to the ground- e.g., a vertical head tube.

Quoted message said:

As you increase the trail & the actual contact point
moves away from the 0-trail contact point, the twisting
forces increase. Now how do you twist this in real life?
A strong wind puts a sideways force on the bike. This
force doesn't affect the rear (fixed) but the front of
the bike can get pushed sideways.

[censored]. The entire bike- including the rear wheel- can get
leaned over by the wind while the bike is being ridden. The
front wheel can get leaned over with the rest of the bike;
there is one more degree of freedom, of course, which is the
turning of the fork along the steering axis. That can happen
on a bike with 100 mm of trail or 0 mm of trail, so long as
the steering axis is not vertical. Your description also
neglects the effects of gravity and the rider's weight, and
also the self-centering action caused by the angle o the
steering axis.

Quoted message said:

If there was zero trail, the front wheel would act fixed
like the rear and the front wheel would still be tracking
the direction of travel.

Again, this is utter malarkey.

Quoted message said:

As trail increases, any rotation of the fork translates
into a larger offset of the contact point and affects the
direction of travel of the bike.

You mean the bike steers? Yet the bike becomes more stable
as trail increases, not less stable. Your description makes
it sound as though increased trail results in less
stability. I think you're confusing trail and fork offset
(also called rake) which have an inverse relationship with
each other.

Quoted message said:

The more flexible the front triangle the more affect this
has on the bike. As far as holes, cracks, etc my belief is
that the shorter the trail the easier it is for the rider
to resist the change caused by the outside influence.
Again consider the differences from zero trail to
something larger.

My experience is that the effects of trail on road anomalies
are minimal and easily countered, whether riding a track
bike with a large amount of trail or a touring bike with
less trail. There is a difference in feel, and IME bikes
with less trail are less affected by lean angles when
cornering.

Much is made about trail, and yet the practical differences
are few and easily compensated by rider skill. The design
parameters of a bicycle are such that variations in trail
are really quite small, compared to the URB experiments
which used utterly huge differences in trail- including one
bike with so much trail that it could balance alone, without
a rider, and was not perturbed by local anomalies in the
road surface (exactly the opposite of your claim). You can
read about it in Whitt and Wilson (and possibly Popadopoulus
and Wilson). There's also an interesting article in the
Rivendell Reader #31, pp 30-33, which compared bikes with
different forks, one resulting in trail of 105 mm and the
other in trail of 37 mm. The "standard" trail for a road
bike is about 60 mm.

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis said:

[email hidden] wrote:

>Benjamin Lewis wrote:
>
>
>>No. My criticism is that Forester is claiming bicycles
>>with long trail have more sensitive steering, when
>>exactly the opposite is true.
>
>Only if you take the party line at face value.

I wasn't aware there was a "party line".

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

You may doubt as much as you want, but I disagree with
many "commonly accepted facts". I'm still not sure what
the commonly accepted facts *are* when it comes to
steering geometry.

That's good.

Quoted message said:

Quoted message said:

Quoted message said:

>Longer trail will help a bike track better but if you
>get inputs to the steering outside of your control
>(wind, holes, bumps, ...) longer trail will actually
>make your bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments. Let's
consider what happens when you push on the head tube of a
bike, holding the bars fixed. With zero trail there will
be no twisting of the head tube around the head tube axis
because the tire/road contact point is directly on the
axis. As you increase the trail & the actual contact point
moves away from the 0-trail contact point, the twisting
forces increase. Now how do you twist this in real life? A
strong wind puts a sideways force on the bike.

I currently have no strong opinions how wind factors into
this, which is why I said "at least with regard to holes
and bumps". I have only rarely experienced steering
trouble due to cross winds, and then only when the wind is
strong enough that I have to lean noticeably in order to
stay upright. I don't use disc wheels, or even "aero"
wheels, which probably would create different steering
effects in the wind.

I've experienced severe wind effects on a bike using regular
wheels & aero wheels. This was the motivation for thought
experiments on what was happening with my bike whilst
struggling with a major handling issue.

Quoted message said:

Quoted message said:

This force doesn't affect the rear (fixed) but the front
of the bike can get pushed sideways. If there was zero
trail, the front wheel would act fixed like the rear and
the front wheel would still be tracking the direction of
travel. As trail increases, any rotation of the fork
translates into a larger offset of the contact point and
affects the direction of travel of the bike.

What makes you think a larger offset of the contact point
affects direction of travel, and what do you think is the
nature of this effect?

If the fork turns due to some input, the tire contact patch
moves away from the center line of the bike. And by the
way, this movement is caused by a change in the steering
angle! For any angle, larger trail = larger change. You are
now in an unbalanced state. Something must change or you
fall over. You must steer the bike back under you.
Unfortunately with a flexible triangle, the counter steer
can cause you to overshoot the centerline, repeat as
necessary. Add lots of wind effects and you end up with a
bike that can barely be ridden.

Quoted message said:

On a vehicle that stays upright when it turns (car,
tricycle), it is the steering angle, not the contact
offset, that affects turning radius. Although bicycle
dynamics are clearly different, it seems unlikely to me
that this would be reversed.

Quoted message said:

The more flexible the front triangle the more affect this
has on the bike. As far as holes, cracks, etc my belief is
that the shorter the trail the easier it is for the rider
to resist the change caused by the outside influence.
Again consider the differences from zero trail to
something larger.

Would you then recommend long distance riders switch from
touring bikes to racing bikes?

No. Large trail is stable. The weight of a loaded touring
bike probably helps keep the entire system moving straight
down the road as the energy required to change the direction
of this system is much higher than that for a lightweight
racing bike.

Once again, MOO Matt

Tim McNamara said:

ML said:

Benjamin Lewis said:

[email hidden] wrote:

>Benjamin Lewis wrote:
>
>
>>No. My criticism is that Forester is claiming bicycles
>>with long trail have more sensitive steering, when
>>exactly the opposite is true.
>
>Only if you take the party line at face value.

I wasn't aware there was a "party line".

There is a "party line" only to the people who want to
appear like they have superior and arcane knowledge. The
rest of us are just trying to separate myth and lore from
reality, and are usually happy to get real facts.

Quoted message said:

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

Which might just be why he's asking the questions and
trying to get reliable information.

Note in the following statement: No. My criticism is that
Forester is claiming bicycles with long

Quoted message said:

Quoted message said:

Quoted message said:

>>trail have more sensitive steering, when exactly
>>the opposite is true.

This isn't asking questions, this is stating his opionion of
trail & sensitivity. The reason for my original append.

Quoted message said:

Quoted message said:

Quoted message said:

>Longer trail will help a bike track better but if you
>get inputs to the steering outside of your control
>(wind, holes, bumps, ...) longer trail will actually
>make your bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments.

Your post is at least as inaccurate, but Benjamin at least
has the wits to be asking for information whereas you are
just pontificating.

Quoted message said:

Let's consider what happens when you push on the head tube
of a bike, holding the bars fixed. With zero trail there
will be no twisting of the head tube around the head tube
axis because the tire/road contact point is directly on
the axis.

This only works as you claim when the steering axis is
normal to the ground- e.g., a vertical head tube.

That's incorrect. If the trail is zero you are turning a
wheel around a
circular circumfernce of zero. It's essentially a point on
the ground.

Quoted message said:

Quoted message said:

As you increase the trail & the actual contact point
moves away from the 0-trail contact point, the twisting
forces increase. Now how do you twist this in real life?
A strong wind puts a sideways force on the bike. This
force doesn't affect the rear (fixed) but the front of
the bike can get pushed sideways.

[censored]. The entire bike- including the rear wheel- can
get leaned over by the wind while the bike is being
ridden. The front wheel can get leaned over with the rest
of the bike; there is one more degree of freedom, of
course, which is the turning of the fork along the
steering axis. That can happen on a bike with 100 mm of
trail or 0 mm of trail, so long as the steering axis is
not vertical. Your description also neglects the effects
of gravity and the rider's weight, and also the self-
centering action caused by the angle o the steering axis.

Of course it'll lean. This isn't about lean. It's about
rotation of the fork in the head tube. Pushing on the rear
end of the bike won't cause a rotation around anything
except the ground because it's fixed in the frame. Read
the append.

Quoted message said:

Quoted message said:

If there was zero trail, the front wheel would act fixed
like the rear and the front wheel would still be tracking
the direction of travel.

Again, this is utter malarkey.

Prove your point to me. If you have zero trail you can't
steer. You'll fall over.

Quoted message said:

Quoted message said:

As trail increases, any rotation of the fork translates
into a larger offset of the contact point and affects the
direction of travel of the bike.

You mean the bike steers? Yet the bike becomes more stable
as trail increases, not less stable. Your description
makes it sound as though increased trail results in less
stability. I think you're confusing trail and fork offset
(also called rake) which have an inverse relationship with
each other.

This is about sensitive steering. A bike can be stable and
still have sensitive steering. And this is about trail, not
rake or offset.

Quoted message said:

Quoted message said:

The more flexible the front triangle the more affect this
has on the bike. As far as holes, cracks, etc my belief is
that the shorter the trail the easier it is for the rider
to resist the change caused by the outside influence.
Again consider the differences from zero trail to
something larger.

My experience is that the effects of trail on road
anomalies are minimal and easily countered, whether riding
a track bike with a large amount of trail or a touring
bike with less trail. There is a difference in feel, and
IME bikes with less trail are less affected by lean angles
when cornering.

Funny thing that you mention track bikes. I think this is a
perfect example of what I'm talking about. Think about it.
You've just contradicted yourself.

Quoted message said:

Much is made about trail, and yet the practical
differences are few and easily compensated by rider skill.
The design parameters of a bicycle are such that
variations in trail are really quite small, compared to
the URB experiments which used utterly huge differences in
trail- including one bike with so much trail that it could
balance alone, without a rider, and was not perturbed by
local anomalies in the road surface (exactly the opposite
of your claim). You can read about it in Whitt and Wilson
(and possibly Popadopoulus and Wilson). There's also an
interesting article in the Rivendell Reader #31, pp 30-33,
which compared bikes with different forks, one resulting
in trail of 105 mm and the other in trail of 37 mm. The
"standard" trail for a road bike is about 60 mm.

I've read a lot of this, including the URBs.

As always, MOO Matt

ML <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis wrote:

>No. My criticism is that Forester is claiming bicycles
>with long trail have more sensitive steering, when
>exactly the opposite is true.

Only if you take the party line at face value.

I wasn't aware there was a "party line".

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

Quoted message said:

Quoted message said:

Longer trail will help a bike track better but if you
get inputs to the steering outside of your control
(wind, holes, bumps, ...) longer trail will actually
make your bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments. Let's
consider what happens when you push on the head tube of a
bike, holding the bars fixed. With zero trail there will
be no twisting of the head tube around the head tube axis
because the tire/road contact point is directly on the
axis. As you increase the trail & the actual contact point
moves away from the 0-trail contact point, the twisting
forces increase. Now how do you twist this in real life? A
strong wind puts a sideways force on the bike. This force
doesn't affect the rear (fixed) but the front of the bike
can get pushed sideways. If there was zero trail, the
front wheel would act fixed like the rear and the front
wheel would still be tracking the direction of travel. As
trail increases, any rotation of the fork translates into
a larger offset of the contact point and affects the
direction of travel of the bike.

I think you have this backwards (if I'm understanding your
thought experiment). Start with a bike whose fork is
straight up and down with no offset (zero trail). If you
turn the handlebars five degrees, the contact patch of the
tire (which can be considered an arrow of sorts) would also
turn five degrees.

Now take the opposite extreme -- the fork juts out from the
frame to the hub running parallel to the ground (like a
chopper, only more so). Now as you turn the handlebars five
degrees, the direction of the contact patch will change
hardly at all. (The movement of the handlebars will
translate into a flopping from side to side of the wheel
above the contact patch.)

The more

Quoted message said:

flexible the front triangle the more affect this has on
the bike. As far as holes, cracks, etc my belief is
that the shorter the trail the easier it is for the
rider to resist the change caused by the outside
influence. Again consider the differences from zero
trail to something larger.

MOO, Matt

Gary Young said:

ML <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Benjamin Lewis said:

[email hidden] wrote:

>Benjamin Lewis wrote:
>
>
>>No. My criticism is that Forester is claiming bicycles
>>with long trail have more sensitive steering, when
>>exactly the opposite is true.
>
>Only if you take the party line at face value.

I wasn't aware there was a "party line".

The "party line" is the commonly accepted facts without
consideration of other possibilities. Benjamin Lewis
obviously believes the party line but I have my doubts if
he's really considered the other possibilities

Quoted message said:

>Longer trail will help a bike track better but if you
>get inputs to the steering outside of your control
>(wind, holes, bumps, ...) longer trail will actually
>make your bike more sensitive. It's a longer lever arm.

This is contrary to my experience, at least with regard
to holes and bumps. Do you have any citations to support
this? If steering does indeed have to do directly with
length of the lever arm, it seems to me that a bump will
result in a fixed lateral displacement, which for a
longer lever arm will result in a smaller change in
steering angle.

No citations just experience & thought experiments. Let's
consider what happens when you push on the head tube of a
bike, holding the bars fixed. With zero trail there will
be no twisting of the head tube around the head tube axis
because the tire/road contact point is directly on the
axis. As you increase the trail & the actual contact point
moves away from the 0-trail contact point, the twisting
forces increase. Now how do you twist this in real life? A
strong wind puts a sideways force on the bike. This force
doesn't affect the rear (fixed) but the front of the bike
can get pushed sideways. If there was zero trail, the
front wheel would act fixed like the rear and the front
wheel would still be tracking the direction of travel. As
trail increases, any rotation of the fork translates into
a larger offset of the contact point and affects the
direction of travel of the bike.

I think you have this backwards (if I'm understanding your
thought experiment). Start with a bike whose fork is
straight up and down with no offset (zero trail). If you
turn the handlebars five degrees, the contact patch of the
tire (which can be considered an arrow of sorts) would
also turn five degrees.

Sorry, with this configuration the contact point only
rotates. THe wheel will turn 5degrees but the contact point
will not move in space

Quoted message said:

Now take the opposite extreme -- the fork juts out from
the frame to the hub running parallel to the ground (like
a chopper, only more so). Now as you turn the handlebars
five degrees, the direction of the contact patch will
change hardly at all. (The movement of the handlebars will
translate into a flopping from side to side of the wheel
above the contact patch.)

It's all a matter of reference. The frame is the reference
so in this example the contact point will move to the side
one tire radius.

Quoted message said:

The more

Quoted message said:

flexible the front triangle the more affect this has on
the bike. As far as holes, cracks, etc my belief is
that the shorter the trail the easier it is for the
rider to resist the change caused by the outside
influence. Again consider the differences from zero
trail to something larger.

MOO, Matt

Quoted message said:

If you have zero trail you can't steer. You'll fall over.

Huh? I think you need to reexamine your model of how bicycle
steering works. Of course you can steer on a bicycle with
zero trail. It's been done. People have even successfully
ridden bicycles with negative trail.

--
Benjamin Lewis

Although the moon is smaller than the earth, it is
farther away.

Benjamin Lewis said:

Quoted message said:

If you have zero trail you can't steer. You'll fall over.

Huh? I think you need to reexamine your model of how
bicycle steering works. Of course you can steer on a
bicycle with zero trail. It's been done. People have even
successfully ridden bicycles with negative trail.

We aren't talking about negtive trail, we're talking about
zero trail. If you have zero trail and you lean your bike
over while riding it, how do you make the bike steer back
under you?

MOO, Matt

Quoted message said:

Benjamin Lewis said:

Quoted message said:

If you have zero trail you can't steer. You'll
fall over.

Huh? I think you need to reexamine your model of how
bicycle steering works. Of course you can steer on a
bicycle with zero trail. It's been done. People have even
successfully ridden bicycles with negative trail.

We aren't talking about negtive trail, we're talking about
zero trail. If you have zero trail and you lean your bike
over while riding it, how do you make the bike steer back
under you?

By turning the handlebars.

I'm not sure what you're confused about here. If the wheel
is turned the front of the bike will move in the direction
of the turn as the bike moves forward.

--
Benjamin Lewis

Evelyn the dog, having undergone further modification,
pondered the significance of short-person behavior in pedal-
depressed panchromatic resonance and other highly ambient
domains... "Arf", she said.

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis said:

[email hidden] wrote:

>If you have zero trail you can't steer. You'll
>fall over.

Huh? I think you need to reexamine your model of how
bicycle steering works. Of course you can steer on a
bicycle with zero trail. It's been done. People have even
successfully ridden bicycles with negative trail.

We aren't talking about negtive trail, we're talking about
zero trail. If you have zero trail and you lean your bike
over while riding it, how do you make the bike steer back
under you?

By turning the handlebars.

I'm not sure what you're confused about here. If the wheel
is turned the front of the bike will move in the direction
of the turn as the bike moves forward.

I believe you are wrong on this but can't really prove it.
Unless you have a bike with true zero trail, you can't prove
your point either so these are just mind exercises.

If you consider your contact patch as a point on the
pavement, turning your handlebars on a bike with zero trail
will not do anything for you. It will continue to try to go
forward (I believe) and ultimately you will end up on the
ground. Why do I say this? For a couple reasons. Consider
what happens to your bike when you lean it to the left while
walking it. The front wheel swings to the right and the bike
turns into the direction it was leaned. This is how a person
is able to ride a bike no handed. The bike naturally does
the steering for you - you affect your direction of travel
by strictly leaning the bike through the saddle. Now
consider what would happen if you leaned a bike with zero
trail to the left - nothing. The bike would just lean, the
front wheel would continue straight down the road. Why?
Because with zero trail there is no torque component in
either the CW or CCW direction. The component of the force
vector which is perpendicular to the fork (the frame of
reference at this point) is applied along the fork
centerline. In order to rotate the fork you must have a
component of force offset by some radius from the center or
rotation. With zero trail, you don't have this. So, if you
were on this bike you would fall down. You can't ride this
bike no handed. Now consider what happens when you are on
the bike. You feel the bike start to fall over as you lean
so you turn the bars to steer into the turn. This is where
the problem comes in. Since you have zero trail all you are
doing is rotating the contact point on the pavement. A true
point source does not have a directional component. In this
case though the reality is that the contact patch looks more
like a square or a rectangle than a point so it will have a
directional component. Will this directional component be
enough to actually direct the bike into the corner? Yes -
the front end will act like a unicycle. I'm not sure how
rideable this bike would be. My instincts tell me only at
very slow speeds.

BTW, I briefly looked through my copy of Bicycle Science
last night & could find no reference to any experiments done
with zero trail bikes. All references were to various
combinations of positive or negative trail bikes. If you can
direct me to references (or to the pages in Bicycle Science)
documenting zero trail bikes I'd love to read them. I can't
think of anything in normal usage that would be equivalent.
Shopping carts, cars, motorcycles, scooters - they all have
trail components.

Jobst, any thoughts on this subject?

MOO, Matt

ML said:

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis wrote:

>[email hidden] wrote:
>
>
>>If you have zero trail you can't steer. You'll fall
>>over.
>
>Huh? I think you need to reexamine your model of how
>bicycle steering works. Of course you can steer on a
>bicycle with zero trail. It's been done. People have
>even successfully ridden bicycles with negative trail.

We aren't talking about negtive trail, we're talking
about zero trail. If you have zero trail and you lean
your bike over while riding it, how do you make the bike
steer back under you?

By turning the handlebars.

I'm not sure what you're confused about here. If the
wheel is turned the front of the bike will move in the
direction of the turn as the bike moves forward.

I believe you are wrong on this but can't really prove it.
Unless you have a bike with true zero trail, you can't
prove your point either so these are just mind exercises.

If you consider your contact patch as a point on the
pavement, turning your handlebars on a bike with zero trail
will not do anything for you. It will continue to try to go
forward (I believe) and ultimately you will end up on the
ground. Why do I say this? For a couple reasons. Consider
what happens to your bike when you lean it to the left
while walking it. The front wheel swings to the right and
the bike turns into the direction it was leaned. This is
how a person is able to ride a bike no handed. The bike
naturally does the steering for you - you affect your
direction of travel by strictly leaning the bike through
the saddle. Now consider what would happen if you leaned a
bike with zero trail to the left - nothing. The bike would
just lean, the front wheel would continue straight down the
road. Why? Because with zero trail there is no torque
component in either the CW or CCW direction. The component
of the force vector which is perpendicular to the fork (the
frame of reference at this point) is applied along the fork
centerline. In order to rotate the fork you must have a
component of force offset by some radius from the center or
rotation. With zero trail, you don't have this. So, if you
were on this bike you would fall down. You can't ride this
bike no handed. Now consider what happens when you are on
the bike. You feel the bike start to fall over as you lean
so you turn the bars to steer into the turn. This is where
the problem comes in. Since you have zero trail all you are
doing is rotating the contact point on the pavement. A true
point source does not have a directional component. In this
case though the reality is that the contact patch looks
more like a square or a rectangle than a point so it will
have a directional component. Will this directional
component be enough to actually direct the bike into the
corner? Yes - the front end will act like a unicycle. I'm
not sure how rideable this bike would be. My instincts tell
me only at very slow speeds.

BTW, I briefly looked through my copy of Bicycle Science
last night & could find no reference to any experiments
done with zero trail bikes. All references were to various
combinations of positive or negative trail bikes. If you
can direct me to references (or to the pages in Bicycle
Science) documenting zero trail bikes I'd love to read
them. I can't think of anything in normal usage that would
be equivalent. Shopping carts, cars, motorcycles, scooters
- they all have trail components.

Jobst, any thoughts on this subject?

MOO, Matt

Dear Matt,

I think that David Jones concluded that we can ride damned
near anything in terms of front-end geometry, although most
bizarre versions are good for little except for parking lot
demonstrations.

Below are some articles mentioned in a post elsewhere by
Jonathan Thornburg:

< [email hidden]>

thp.univie.ac.athome.htmlOpen ↗

Carl Fogel

David E. H. Jones "The Stability of the Bicycle" Physics
Today , April 1970, 34-40

Framk Rowland Whitt and David Gordon Wilson "Bicycling
Science", 2nd edition MIT Press, 1982, ISBN 0-262-73060-X
(paperback), -23111-5 (hardcover) ... this book has a
chapter devoted to stability,

J. Lowell and H. D. McKell "The Stability of
Bicycles" American Journal of Physics 50(12), Dec
1987, 1106-1112

G Franke, W Suhr, and F Reisz, "An advanced model of
bicycle dynamics", European Journal of Physics 11
(1990) 116-121

John Maddox's report of the Franke/Suhr/Reisz paper in
Nature 346, 2 Aug 1990, p 407.

Quoted message said:

Benjamin Lewis said:

Quoted message said:

Benjamin Lewis wrote:
> [email hidden] wrote:
>
>> If you have zero trail you can't steer. You'll fall
>> over.
>
> Huh? I think you need to reexamine your model of how
> bicycle steering works. Of course you can steer on a
> bicycle with zero trail. It's been done. People have
> even successfully ridden bicycles with negative trail.

We aren't talking about negtive trail, we're talking
about zero trail. If you have zero trail and you lean
your bike over while riding it, how do you make the bike
steer back under you?

By turning the handlebars. I'm not sure what you're
confused about here. If the wheel is turned the front of
the bike will move in the direction of the turn as the
bike moves forward.

I believe you are wrong on this but can't really prove it.
Unless you have a bike with true zero trail, you can't
prove your point either so these are just mind exercises.

Like I said before, it's been done, e.g.:
bikernet.comsugarbear.aspOpen ↗

From Scott Hand's PhD thesis, available at
tam.cornell.edubicycles.htmlOpen ↗

d(t_r)/dt = (c_f/c_w)d(phi)/dt + phi*d(y_r)/dt*cos(l)/c_w

where t_r = direction rear frame of bicycle is heading c_f =
mechanical trail (which = 0 when trail = 0) c_w = wheelbase
phi = steering angle d(y_r)/dt = speed (approximately) l =
90 - headtube angle

With zero trail, the first term on the right becomes zero,
but the second term, which is generally larger, does not.
This expression essentially determines how fast the bike
is turning.

Quoted message said:

If you consider your contact patch as a point on the
pavement, turning your handlebars on a bike with zero
trail will not do anything for you. It will continue to
try to go forward (I believe)

This would mean the front tire would be sliding rather than
rolling. Why would you think this would start to happen, and
why only on a zero trail bike?

Quoted message said:

and ultimately you will end up on the ground. Why do I say
this? For a couple reasons. Consider what happens to your
bike when you lean it to the left while walking it. The
front wheel swings to the right and the bike turns into
the direction it was leaned. This is how a person is able
to ride a bike no handed. The bike naturally does the
steering for you - you affect your direction of travel by
strictly leaning the bike through the saddle. Now consider
what would happen if you leaned a bike with zero trail to
the left - nothing. The bike would just lean, the front
wheel would continue straight down the road. Why? Because
with zero trail there is no torque component in either the
CW or CCW direction.

You are forgetting:
- torque applied by the rider to the handlebars
- torque due to gyroscopic effects of the front wheel
- there is also torque in the proper direction if the centre
of mass of the front assembly (front wheel + fork,
handlbars, etc) is in front of the steering axis

Quoted message said:

The component of the force vector which is perpendicular
to the fork (the frame of reference at this point) is
applied along the fork centerline. In order to rotate the
fork you must have a component of force offset by some
radius from the center or rotation. With zero trail, you
don't have this. So, if you were on this bike you would
fall down. You can't ride this bike no handed. Now
consider what happens when you are on the bike. You feel
the bike start to fall over as you lean so you turn the
bars to steer into the turn. This is where the problem
comes in. Since you have zero trail all you are doing is
rotating the contact point on the pavement. A true point
source does not have a directional component. In this case
though the reality is that the contact patch looks more
like a square or a rectangle than a point so it will have
a directional component. Will this directional component
be enough to actually direct the bike into the corner? Yes
- the front end will act like a unicycle. I'm not sure how
rideable this bike would be. My instincts tell me only at
very slow speeds.

A typical model would constrain even a point contact patch
not to slide on the ground, even with idealized knife-blade
wheels. A model that lets the contact point slide would only
be useful for modeling bicycles on, say, ice rinks. I think
you'll find *any* bicycle is difficult to steer in such a
situation.

--
Benjamin Lewis

I regret to say that we of the FBI are powerless to act in
cases of oral-genital intimacy, unless it has in some way
obstructed interstate commerce. -- J. Edgar Hoover

Quoted message said:

ML said:

Benjamin Lewis said:

[email hidden] wrote:

>Benjamin Lewis wrote:
>
>
>>[email hidden] wrote:
>>
>>
>>
>>>If you have zero trail you can't steer. You'll fall
>>>over.
>>
>>Huh? I think you need to reexamine your model of how
>>bicycle steering works. Of course you can steer on a
>>bicycle with zero trail. It's been done. People have
>>even successfully ridden bicycles with negative trail.
>
>We aren't talking about negtive trail, we're talking
>about zero trail. If you have zero trail and you lean
>your bike over while riding it, how do you make the bike
>steer back under you?

By turning the handlebars.

I'm not sure what you're confused about here. If the
wheel is turned the front of the bike will move in the
direction of the turn as the bike moves forward.

I believe you are wrong on this but can't really prove it.
Unless you have a bike with true zero trail, you can't
prove your point either so these are just mind exercises.

If you consider your contact patch as a point on the
pavement, turning your handlebars on a bike with zero
trail will not do anything for you. It will continue to
try to go forward (I believe) and ultimately you will end
up on the ground. Why do I say this? For a couple
reasons. Consider what happens to your bike when you lean
it to the left while walking it. The front wheel swings
to the right and the bike turns into the direction it was
leaned. This is how a person is able to ride a bike no
handed. The bike naturally does the steering for you -
you affect your direction of travel by strictly leaning
the bike through the saddle. Now consider what would
happen if you leaned a bike with zero trail to the left -
nothing. The bike would just lean, the front wheel would
continue straight down the road. Why? Because with zero
trail there is no torque component in either the CW or
CCW direction. The component of the force vector which is
perpendicular to the fork (the frame of reference at this
point) is applied along the fork centerline. In order to
rotate the fork you must have a component of force offset
by some radius from the center or rotation. With zero
trail, you don't have this. So, if you were on this bike
you would fall down. You can't ride this bike no handed.
Now consider what happens when you are on the bike. You
feel the bike start to fall over as you lean so you turn
the bars to steer into the turn. This is where the
problem comes in. Since you have zero trail all you are
doing is rotating the contact point on the pavement. A
true point source does not have a directional component.
In this case though the reality is that the contact patch
looks more like a square or a rectangle than a point so
it will have a directional component. Will this
directional component be enough to actually direct the
bike into the corner? Yes - the front end will act like a
unicycle. I'm not sure how rideable this bike would be.
My instincts tell me only at very slow speeds.

BTW, I briefly looked through my copy of Bicycle Science
last night & could find no reference to any experiments
done with zero trail bikes. All references were to various
combinations of positive or negative trail bikes. If you
can direct me to references (or to the pages in Bicycle
Science) documenting zero trail bikes I'd love to read
them. I can't think of anything in normal usage that would
be equivalent. Shopping carts, cars, motorcycles, scooters
- they all have trail components.

Jobst, any thoughts on this subject?

MOO, Matt

Dear Matt,

I think that David Jones concluded that we can ride damned
near anything in terms of front-end geometry, although
most bizarre versions are good for little except for
parking lot demonstrations.

Below are some articles mentioned in a post elsewhere by
Jonathan Thornburg:

< [email hidden]>

thp.univie.ac.athome.htmlOpen ↗

Carl Fogel

David E. H. Jones "The Stability of the Bicycle" Physics
Today , April 1970, 34-40

Framk Rowland Whitt and David Gordon Wilson "Bicycling
Science", 2nd edition MIT Press, 1982, ISBN 0-262-73060-
X (paperback), -23111-5 (hardcover) ... this book has a
chapter devoted to stability,

J. Lowell and H. D. McKell "The Stability of Bicycles"
American Journal of Physics 50(12), Dec 1987, 1106-
1112

G Franke, W Suhr, and F Reisz, "An advanced model of
bicycle dynamics", European Journal of Physics 11
(1990) 116-121

John Maddox's report of the Franke/Suhr/Reisz paper in
Nature 346, 2 Aug 1990, p 407.

Carl:

The URL for jthorn is not valid. I did a websearch and found
no other information.

Thanks, Matt