Bicycle dynamics vs. motorcycle dynamics

[Blair P. Houghton]

They're exactly the same, except for the enormous differences
caused by the dichotomy between the mass ratios of rider and
mount.

On a bicycle, you're 80-90% of the mass, which gives you
all the control.

On a motorcycle, you're 10-50% of the mass, which means
you're just along for the ride, making suggestions.

Counterweighting and countersteer exist in both paradigms.
As do gyroscopic effects, but I don't think they're the
real story for either.

Braking is only different in that a motorcycle/rider
system's lower center of gravity lets you use the front
brake more aggressively.

We've discussed this stuff before, but now I've got about
1500 miles of experience on a motorbike in the past month,
so I'm adding my two spokes' worth.

--Blair
"And there's more room for biker
chicks on the back of one..."

[Tom Keats]

In article >,
Blair P. Houghton > writes:
> They're exactly the same, except for the enormous differences
> caused by the dichotomy between the mass ratios of rider and
> mount.
>
> On a bicycle, you're 80-90% of the mass, which gives you
> all the control.
>
> On a motorcycle, you're 10-50% of the mass, which means
> you're just along for the ride, making suggestions.
>
> Counterweighting and countersteer exist in both paradigms.
> As do gyroscopic effects, but I don't think they're the
> real story for either.

I suspect fore-&-aft balance when going uphill might be
more of an issue with bicycles than with motorcycles.
hmmmm ... I wonder if difficulty with weighting the wheels
has anything to do with some recumbent bicycle designs
being rather sluggish on upslopes?


cheers,
Tom

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[Matt O'Toole]

Tom Keats wrote:

> I suspect fore-&-aft balance when going uphill might be
> more of an issue with bicycles than with motorcycles.
> hmmmm ... I wonder if difficulty with weighting the wheels
> has anything to do with some recumbent bicycle designs
> being rather sluggish on upslopes?

Nope, it's being unable to stand.

Good recumbent riders can corner and brake like demons.

Matt O.

[Bob]

Blair P. Houghton wrote:
> They're exactly the same, except for the enormous differences

If I weren't so short I'd be much taller.

Regards,
Bob Hunt

[Chalo]

Blair P. Houghton wrote:
>
> They're exactly the same, except for the enormous differences
> caused by the dichotomy between the mass ratios of rider and
> mount.
>
> On a bicycle, you're 80-90% of the mass, which gives you
> all the control.
>
> On a motorcycle, you're 10-50% of the mass, which means
> you're just along for the ride, making suggestions.
>
> Counterweighting and countersteer exist in both paradigms.
> As do gyroscopic effects, but I don't think they're the
> real story for either.
>
> Braking is only different in that a motorcycle/rider
> system's lower center of gravity lets you use the front
> brake more aggressively.

There is another factor you have not addressed-- that of the staggering
differences in gyroscopic forces between bicycles and motorcycles.

Each wheel of a motorcycle can weigh more than a bicycle, and so can
the crank assembly. And they all three turn at a multiple of the
speeds typical for a bicycle wheel. This is a major reason for both a
motorcycle's impressive stability and the force required at the bars to
steer a motorcycle.

Having ridden bicycles for transportation for 18 years and motorcycles
for 10, I don't find that much about riding them that is directly
comparable. But all my bikes have been 600+ lbs with lots of
horsepower, and I'm willing to believe that a very lightweight
motorcycle would feel more bicycle-like.

Chalo Colina

[Brian Wax]

Tough comparison. Yes the weight of the wheels create a gyroscopic effect.
Then again it is relative to mass etc. Personally, a bicycle handles the
same depending upon speed. The speed is relative too. Bicycle and motorcycle
experience have been extremely valuable. I have not slid a bicycle at 70 mph
but I have a motor cycle. The difference is your ability to translate your
input into controllable output. To me they are the same input under
different speeds. If you know how to counter steer, you can do it on a
bicycle. The same thing is true with trail braking. The difference lies in
your ability to understand the platform you are on. On my road bicycle,
under heavy braking, I am off the saddle and over the rear wheel. On my
Ducat, I sit dead center ready to shift my weight to the rear.


"Chalo" > wrote in message
oups.com...
> Blair P. Houghton wrote:
>>
>> They're exactly the same, except for the enormous differences
>> caused by the dichotomy between the mass ratios of rider and
>> mount.
>>
>> On a bicycle, you're 80-90% of the mass, which gives you
>> all the control.
>>
>> On a motorcycle, you're 10-50% of the mass, which means
>> you're just along for the ride, making suggestions.
>>
>> Counterweighting and countersteer exist in both paradigms.
>> As do gyroscopic effects, but I don't think they're the
>> real story for either.
>>
>> Braking is only different in that a motorcycle/rider
>> system's lower center of gravity lets you use the front
>> brake more aggressively.
>
> There is another factor you have not addressed-- that of the staggering
> differences in gyroscopic forces between bicycles and motorcycles.
>
> Each wheel of a motorcycle can weigh more than a bicycle, and so can
> the crank assembly. And they all three turn at a multiple of the
> speeds typical for a bicycle wheel. This is a major reason for both a
> motorcycle's impressive stability and the force required at the bars to
> steer a motorcycle.
>
> Having ridden bicycles for transportation for 18 years and motorcycles
> for 10, I don't find that much about riding them that is directly
> comparable. But all my bikes have been 600+ lbs with lots of
> horsepower, and I'm willing to believe that a very lightweight
> motorcycle would feel more bicycle-like.
>
> Chalo Colina
>

[Just zis Guy, you know?]

I submit that on or about Sat, 4 Jun 2005 20:32:49 -0400, the person
known to the court as "Matt O'Toole" > made a
statement > in Your Honour's bundle) to
the following effect:

>> I wonder if difficulty with weighting the wheels
>> has anything to do with some recumbent bicycle designs
>> being rather sluggish on upslopes?

>Nope, it's being unable to stand.

Nope, it's partly blood flow dynamics and partly the weight of the
bike. The ability to stand is more than offset by the ability to push
against the seat, giving tractive effort greater than your mass alone
would allow.

A lightweight recumbent with a fit rider can climb every bit as well
as a wedgie (e.g. the hill climb contest at last year's Cyclefest
which was won by Howard on a recumbent trike with a chainwheel the
size of a dustbin lid, against a field which included lightweight
spaceframe Moultons and other uprights).

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[Ben Kaufman]

On Sat, 04 Jun 2005 23:30:48 GMT, Blair P. Houghton > wrote:

>They're exactly the same, except for the enormous differences
>caused by the dichotomy between the mass ratios of rider and
>mount.
<snip>

In addition to things others have mentioned, bicycles usually have a much lower
front wheel rake angle and shorter wheelbase. This makes them more agile at
low speeds but less stable at higher speeds.


Ben

[Tom Keats]

In article >,
"Just zis Guy, you know?" > writes:
> I submit that on or about Sat, 4 Jun 2005 20:32:49 -0400, the person
> known to the court as "Matt O'Toole" > made a
> statement > in Your Honour's bundle) to
> the following effect:
>
>>> I wonder if difficulty with weighting the wheels
>>> has anything to do with some recumbent bicycle designs
>>> being rather sluggish on upslopes?
>
>>Nope, it's being unable to stand.
>
> Nope, it's partly blood flow dynamics and partly the weight of the
> bike. The ability to stand is more than offset by the ability to push
> against the seat, giving tractive effort greater than your mass alone
> would allow.

When a lot of people think about balancing on a bicycle,
they seem to mostly think about left-&-right balancing.
But I'm thinking about the fore-&-aft balancing that comes
into play when riding on slopes -- i.e: the weight placed
on either wheel, which I think can be adjusted with more
subtlety than just by standing.

Anyhow, I'm just considering this might be one aspect where
the dynamics differ between bicycles and motorcycles (and
other vehicles where the rider's shifting their weight
around is more-or-less precluded.)


cheers,
Tom

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Above address is just a spam midden.
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[[email protected]]

Just zis Guy, you know? wrote, in response to:
>
> >> I wonder if difficulty with weighting the wheels
> >> has anything to do with some recumbent bicycle designs
> >> being rather sluggish on upslopes?
>
> >Nope, it's being unable to stand.
>
> Nope, it's partly blood flow dynamics and partly the weight of the
> bike. The ability to stand is more than offset by the ability to push
> against the seat, giving tractive effort greater than your mass alone
> would allow.

I'm not sure about that last idea. Yes, you can get more force out of
your legs than your weight, and a recumbent gives you the chance to do
that.

But ISTM that on an upright, climbing when standing, you're bringing
many more muscles into play. I believe I use my arms, etc. to
partially lift my weight, which I then "deposit" onto the upper pedal.
I thus put some work done by upper body into forward propulsion.

It's obvious to me I can do this even when my quads are so fatigued I
can barely pedal uphill seated, so there's _something_ contributing
beyond what my quads can produce.

> A lightweight recumbent with a fit rider can climb every bit as well
> as a wedgie (e.g. the hill climb contest at last year's Cyclefest
> which was won by Howard on a recumbent trike with a chainwheel the
> size of a dustbin lid, against a field which included lightweight
> spaceframe Moultons and other uprights).

This may be true for the very lightest recumbents, but certainly not
for most of them. And part of the gain may be aerodynamics (depending
which way the wind was blowing that day). I was surprised when I
noticed that even a slight breeze still makes a detectable difference
climbing the hill on my way home. The slope in the steeper parts runs
from about 5% to 10%, so I'm not moving fast; but a tailwind still
helps!

- Frank Krygowski

[Just zis Guy, you know?]

At Sun, 5 Jun 2005 11:01:43 -0700, message
> was posted by
(Tom Keats), including some, all or none of the following:

>When a lot of people think about balancing on a bicycle,
>they seem to mostly think about left-&-right balancing.
>But I'm thinking about the fore-&-aft balancing that comes
>into play when riding on slopes -- i.e: the weight placed
>on either wheel, which I think can be adjusted with more
>subtlety than just by standing.

I don't think this comes into play except on the very steepest hills.
It certainly hasn't been an issue for me yet.

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[Just zis Guy, you know?]

At 5 Jun 2005 11:56:45 -0700, message
. com> was posted by
, including some, all or none of the following:

>> Nope, it's partly blood flow dynamics and partly the weight of the
>> bike. The ability to stand is more than offset by the ability to push
>> against the seat, giving tractive effort greater than your mass alone
>> would allow.

>ISTM that on an upright, climbing when standing, you're bringing
>many more muscles into play. I believe I use my arms, etc. to
>partially lift my weight, which I then "deposit" onto the upper pedal.
>I thus put some work done by upper body into forward propulsion.

I don't think you put in any meaningful amount of effort through these
mechanisms. And that's before we even get into the issues of
differential strength (I can easily leg press several times my own
weight, which is far more than I can manage with any arm weight
exercise).

>It's obvious to me I can do this even when my quads are so fatigued I
>can barely pedal uphill seated, so there's _something_ contributing
>beyond what my quads can produce.

Change of posture - different muscle recruitment. That is an issue on
a 'bent, and it's one reason you have to build up your 'bent legs,
because you can't recruit other muscles as they fatigue.

>> A lightweight recumbent with a fit rider can climb every bit as well
>> as a wedgie (e.g. the hill climb contest at last year's Cyclefest
>> which was won by Howard on a recumbent trike with a chainwheel the
>> size of a dustbin lid, against a field which included lightweight
>> spaceframe Moultons and other uprights).

>This may be true for the very lightest recumbents, but certainly not
>for most of them. And part of the gain may be aerodynamics (depending
>which way the wind was blowing that day).

The former - up to a point. I believe Howard's trike weighs in at
well over 30lb, which is heavy for a bike and much heavier than the
25lb Moulton. In any case, I weigh 180lb, so a couple of lb on the
bike is hardly going to make a big difference. The latter - not on a
hill-climb race (Deliberately steep hill), I think. And it was, if I
recall correctly, a flat calm that evening.

>I was surprised when I
>noticed that even a slight breeze still makes a detectable difference
>climbing the hill on my way home. The slope in the steeper parts runs
>from about 5% to 10%, so I'm not moving fast; but a tailwind still
>helps!

Why do you think I bought the recumbent? ;-)

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[[email protected]]

Just zis Guy, you know? wrote:
> At 5 Jun 2005 11:56:45 -0700, message
> . com> was posted by
> , including some, all or none of the following:
>
> >ISTM that on an upright, climbing when standing, you're bringing
> >many more muscles into play. I believe I use my arms, etc. to
> >partially lift my weight, which I then "deposit" onto the upper pedal.
> >I thus put some work done by upper body into forward propulsion.
>
> I don't think you put in any meaningful amount of effort through these
> mechanisms. And that's before we even get into the issues of
> differential strength (I can easily leg press several times my own
> weight, which is far more than I can manage with any arm weight
> exercise).
>
> >It's obvious to me I can do this even when my quads are so fatigued I
> >can barely pedal uphill seated, so there's _something_ contributing
> >beyond what my quads can produce.
>
> Change of posture - different muscle recruitment.

"Different muscle recruitment" is, I think, short for what I described!

- Frank Krygowski

[Just zis Guy, you know?]

At 5 Jun 2005 13:50:20 -0700, message
. com> was posted by
, including some, all or none of the following:

>"Different muscle recruitment" is, I think, short for what I described!

Not really; they are still leg muscles. I can get more effort on a
'bent (I can get wheelspin on the flat in some circumstances).

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[[email protected]]

Just zis Guy, you know? wrote:
> At 5 Jun 2005 13:50:20 -0700, message
> . com> was posted by
> , including some, all or none of the following:
>
> >"Different muscle recruitment" is, I think, short for what I described!
>
> Not really; they are still leg muscles. I can get more effort on a
> 'bent (I can get wheelspin on the flat in some circumstances).

OK. I think I'm recruiting other muscles besides leg muscles.

- Frank Krygowski

[Tom Keats]

In article >,
"Just zis Guy, you know?" > writes:
> At Sun, 5 Jun 2005 11:01:43 -0700, message
> > was posted by
> (Tom Keats), including some, all or none of the following:
>
>>When a lot of people think about balancing on a bicycle,
>>they seem to mostly think about left-&-right balancing.
>>But I'm thinking about the fore-&-aft balancing that comes
>>into play when riding on slopes -- i.e: the weight placed
>>on either wheel, which I think can be adjusted with more
>>subtlety than just by standing.
>
> I don't think this comes into play except on the very steepest hills.
> It certainly hasn't been an issue for me yet.

Interesting. I find myself shifting my weight to & fro even
on somewhat less acute slopes. If you ever come out to
Vancouver BC, I could show you what I mean, on Collingwood
Street or Ellesmere Street (up Capitol Hill in our
Siamese-twin city of Burnaby.) Of course, some of that
shifting is me scootching /back/ in the saddle, so as to get
a slightly better leg extension and apply more force to the
cranks. In that regard I guess that's like trying to emulate
the recumbent position. It works for a while, but eventually
my front wheel wants more weight on it too.


cheers,
Tom

one of my favourites for bloody-minded,
therapeutic hill repeats.

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[J.V.]

"Just zis Guy, you know?" > wrote in message
...
> I submit that on or about Sat, 4 Jun 2005 20:32:49 -0400, the person
> known to the court as "Matt O'Toole" > made a
> statement > in Your Honour's bundle) to
> the following effect:
>
> >> I wonder if difficulty with weighting the wheels
> >> has anything to do with some recumbent bicycle designs
> >> being rather sluggish on upslopes?
>
> >Nope, it's being unable to stand.
>
> Nope, it's partly blood flow dynamics and partly the weight of the
> bike. The ability to stand is more than offset by the ability to push
> against the seat, giving tractive effort greater than your mass alone
> would allow.
>

I could believe the blood flow part. But, I just don't believe that pushing
against the back of the seat makes up for using your weight while standing
(at least not for me). With standing you have in my case 150 lbs of
practically free (energy consumption wise) force twice per revolution.
Pushing against the seat takes considerably more effort. Over a sustained
climb I don't think the same person (who had equally trained bent and df
trained muscles) would see the same performance pushing against the seat vs.
standing on a df. I rode a swb for a couple years and got pretty good at
it. Climbing was not an issue, but I could never compete with myself on a
df.



> A lightweight recumbent with a fit rider can climb every bit as well
> as a wedgie (e.g. the hill climb contest at last year's Cyclefest
> which was won by Howard on a recumbent trike with a chainwheel the
> size of a dustbin lid, against a field which included lightweight
> spaceframe Moultons and other uprights).
>
> Guy
> --
> May contain traces of irony. Contents liable to settle after posting.
> http://www.chapmancentral.co.uk
>
> 85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[Blair P. Houghton]

Chalo > wrote:
>There is another factor you have not addressed-- that of the staggering
>differences in gyroscopic forces between bicycles and motorcycles.

Given the mass of motorcycle chassis and rider, I don't
think the gyroscopic forces are as significant to the
process as everyone says. I'm sure they have to be
included, but I doubt they're as big a contribution as
people make out.

>Each wheel of a motorcycle can weigh more than a bicycle, and so can
>the crank assembly. And they all three turn at a multiple of the
>speeds typical for a bicycle wheel. This is a major reason for both a
>motorcycle's impressive stability and the force required at the bars to
>steer a motorcycle.

I think both are explained mostly by the geometry.

Both motorcycles and bicycles get a lot more stable when
the wheel is moving faster and can correct errors quicker.

>Having ridden bicycles for transportation for 18 years and motorcycles
>for 10, I don't find that much about riding them that is directly
>comparable. But all my bikes have been 600+ lbs with lots of
>horsepower, and I'm willing to believe that a very lightweight
>motorcycle would feel more bicycle-like.

Mine is about 520 lbs wet, and with me on it is about 700 lbs.

The small motions that lead to the big changes that control
the two systems are the same. Every turn of a bicycle
starts with a counter-turn to kick the wheels out and lean
the bike. Just as for a motorcycle. Because of the fork
trail, the forces from the ground and the head turn the
fork to create a dihedral angle between the front and rear
wheels, determining the turning radius. The result is that
the same direction of force on the handlebar (a forward push
on the handle collateral with the turning direction) initiates
the turn and then keeps the fork from over-turning. It's less
noticeable on a bicycle because the system is much lighter and
the trail is much shorter.

So far, I haven't needed to induce gyroscopy. But I
haven't written out the equations myself yet. It's going
to add something to the torque at the bars, it's just a
matter of how much. I saw something silly the other day:
a book written by engineers at Aprilia who said that it
was primarily gyroscopy that caused the front wheel to
countersteer into a turn. But countersteer works even
better at lower-to-middle speeds, and I guess they never
dropped a bike at 0 mph.

Precession acts pretty slowly anyway, so I find it hard
to believe that any quick swerving could be accomplished
by waiting for a wheel to precess.

One of these days I'll get a hair up and put the whole system
down on paper.

--Blair
"Then turn around, grab the bars and
the seat, and pick it up."

[Blair P. Houghton]

Brian Wax > wrote:
>Tough comparison. Yes the weight of the wheels create a gyroscopic effect.
>Then again it is relative to mass etc. Personally, a bicycle handles the
>same depending upon speed. The speed is relative too. Bicycle and motorcycle
>experience have been extremely valuable. I have not slid a bicycle at 70 mph
>but I have a motor cycle. The difference is your ability to translate your
>input into controllable output. To me they are the same input under
>different speeds. If you know how to counter steer, you can do it on a
>bicycle.

Doesn't matter if you know how. You do it every time
you make a bicycle turn. You aim the front wheel to the
outside of the current balanced trajectory, the wheels kick
that way, the bike heels over into the turn, the trail
forces the fork to fold, and you turn, at a constant radius
if the front wheel finds a new balanced trajectory at the
given lean angle.

To straighten up, you aim the front wheel inside the
balanced trajectory and the wheels come up under you.

In fact, to accomplish this, you reduce your force on
the bars. This allows the fork to fold a little farther,
aiming the front wheel inside the balanced trajectory
you're on.

Both a motorcycle and a bicycle will do this automatically.

It's how you can ride a motorcycle at all, given how wee
you are compared to it; and how you can ride a bicycle
with no hands on the bars.

Watch it work sometimes. You'll catch the constant wiggling
of the machine when you reduce your input force to 0.

In essence, you're ALWAYS falling on either one. But they're
designed to correct the fall when they're rolling forward.

Pretty nifty bit of serendipity, considering how little chance
there was that anyone had a clue how to do the math when the
in-line two-wheeled vehicle was invented.

>The same thing is true with trail braking. The difference lies in
>your ability to understand the platform you are on. On my road bicycle,
>under heavy braking, I am off the saddle and over the rear wheel. On my
>Ducat, I sit dead center ready to shift my weight to the rear.

That's got to do with the CG. On a bicycle, it's well
above the seat. On a motorcycle, it's (usually) well
below the seat.

The really huge difference is the effect of transient
inputs on you vs. the vehicle. If you high-side on a
bicycle you might fly a few feet; but if you do it on a
motorcycle at the same speed, you can go a much longer way
in the air because the bike will be transferring its large
momentum to a much less massive object (you).

--Blair
"An experiment I intend not to perform
on myself."

[Blair P. Houghton]

Ben Kaufman > wrote:
>On Sat, 04 Jun 2005 23:30:48 GMT, Blair P. Houghton > wrote:
>
>>They're exactly the same, except for the enormous differences
>>caused by the dichotomy between the mass ratios of rider and
>>mount.
><snip>
>
>In addition to things others have mentioned, bicycles usually have a much lower
>front wheel rake angle and shorter wheelbase. This makes them more agile at
>low speeds but less stable at higher speeds.

I wonder if there are any sportbikes with rakes and wheelbases near
the average racing bike...

--Blair
"Wouldn't be too surprised."

[Just zis Guy, you know?]

On Mon, 06 Jun 2005 04:32:28 GMT, "J.V." > wrote:

>I could believe the blood flow part. But, I just don't believe that pushing
>against the back of the seat makes up for using your weight while standing
>(at least not for me). With standing you have in my case 150 lbs of
>practically free (energy consumption wise) force twice per revolution.
>Pushing against the seat takes considerably more effort.

Same force, same effort.

>Over a sustained
>climb I don't think the same person (who had equally trained bent and df
>trained muscles) would see the same performance pushing against the seat vs.
>standing on a df. I rode a swb for a couple years and got pretty good at
>it. Climbing was not an issue, but I could never compete with myself on a
>df.

I, too, am somewhat faster uphill on a wedgie. Some wedgies, anyway.
But I have never had the chance to compare like with like weightwise,
and as noted elsewhere there are plenty of examples of 'bent riders
beating mixed fields even where significant climbing is involved (Bram
Moens springs to mind here).

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at CHS, Puget Sound

[[email protected]]

Blair P. Houghton wrote:
>
> So far, I haven't needed to induce gyroscopy. But I
> haven't written out the equations myself yet....
>
> One of these days I'll get a hair up and put the whole system
> down on paper.
>

Before you do the equations, take a look at what others have attempted.

AFAIK, nobody has succeeded in a complete mathematical model of bike
stability and handling, and many have tried. It's an excellent example
of something that's simple in practice and devilishly difficult in
theory.

You might want to start with _Bicycling Science_ by Wilson et. al.

- Frank Krygowski

[[email protected]]

Just zis Guy, you know? wrote:
>
> I, too, am somewhat faster uphill on a wedgie. Some wedgies, anyway.
> But I have never had the chance to compare like with like weightwise...

That would be a quick and easy thing to do. Surely, you can find 15
pounds of steel to clamp to your wedgie frame?

You could, of course, clamp on 15 pounds of aluminum. But that would
be too harsh. ;-)

- Frank Krygowski

[Just zis Guy, you know?]

At 6 Jun 2005 10:01:48 -0700, message
. com> was posted by
, including some, all or none of the following:

>> I, too, am somewhat faster uphill on a wedgie. Some wedgies, anyway.
>> But I have never had the chance to compare like with like weightwise...

>That would be a quick and easy thing to do. Surely, you can find 15
>pounds of steel to clamp to your wedgie frame?

Damn, Frank, that's so simple it's brilliant! I will try it.

>You could, of course, clamp on 15 pounds of aluminum. But that would
>be too harsh. ;-)

Plus it might fatigue and break. Ti is the only way to go here. I
wonder how much 15lb of Ti costs? Or maybe I should go with carbon
fibre.

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[Brian Wax]

As far as gyroscopic goes, the spinning mass of the wheels adds a great deal
of stability. That is why many of the after market wheels are pounds lighter
and the more exotic motorcycles have much lighter wheels. The lighter the
wheel, the easier it is to change direction. This also has a big effect on
the suspension characteristics.

The dynamics of the bike and motorcycle are very similar as Blair has
pointed out. Steering trail and rake make for more or less rider input for
tuning. This also means stability. The more slack geometries or laid back
seat tube make for a more solid platform. You pick what works best for you
or what you feel more comfortable on. My CR 250 Honda and my Ducati have
short wheel bases and steeper steering angles. These bikes turn well but are
much more nervous at speed. I had to put steering dampeners on both bikes.
While accelerating out of turns, the front wheel would shake back and forth
violently.

My Colnago is a much more stable and predicable steerer in contrast to my
Crit geometry Serotta. Under hard braking I put my butt way over the back
wheel of the Serotta to compensate for the steeper seat post angle. The
rider will/should address his/her inputs according to the geometry.

Brian

> wrote in message
ups.com...
>
>
> Blair P. Houghton wrote:
>>
>> So far, I haven't needed to induce gyroscopy. But I
>> haven't written out the equations myself yet....
>>
>> One of these days I'll get a hair up and put the whole system
>> down on paper.
>>
>
> Before you do the equations, take a look at what others have attempted.
>
> AFAIK, nobody has succeeded in a complete mathematical model of bike
> stability and handling, and many have tried. It's an excellent example
> of something that's simple in practice and devilishly difficult in
> theory.
>
> You might want to start with _Bicycling Science_ by Wilson et. al.
>
> - Frank Krygowski
>

[Benjamin Lewis]

wrote:

>
>
> Blair P. Houghton wrote:
>>
>> So far, I haven't needed to induce gyroscopy. But I
>> haven't written out the equations myself yet....
>>
>> One of these days I'll get a hair up and put the whole system
>> down on paper.
>>
>
> Before you do the equations, take a look at what others have attempted.
>
> AFAIK, nobody has succeeded in a complete mathematical model of bike
> stability and handling, and many have tried. It's an excellent example
> of something that's simple in practice and devilishly difficult in
> theory.
>
> You might want to start with _Bicycling Science_ by Wilson et. al.

This is the best I've found:

http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/overview_papers_and_links.htm

or equivalently:

http://tinyurl.com/a37v5

--
Benjamin Lewis

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

[Just zis Guy, you know?]

At Mon, 06 Jun 2005 11:08:18 -0700, message
> was posted by Benjamin Lewis
>, including some, all or none of the following:

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

From what?

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[Benjamin Lewis]

Just zis Guy wrote:

> At Mon, 06 Jun 2005 11:08:18 -0700, message
> > was posted by Benjamin Lewis
> >, including some, all or none of the following:
>
>> Although the moon is smaller than the earth, it is farther away.
>
> From what?

I don't know. Is there any possible answer to your question that would
make the statement useful in any way?

--
Benjamin Lewis

Seeing is deceiving. It's eating that's believing.
-- James Thurber

[Just zis Guy, you know?]

At Mon, 06 Jun 2005 11:55:10 -0700, message
> was posted by Benjamin Lewis
>, including some, all or none of the following:

>>> Although the moon is smaller than the earth, it is farther away.
>> From what?
>I don't know. Is there any possible answer to your question that would
>make the statement useful in any way?

I feel the need to consult the magic 8-ball.

"Reply hazy, try again"

Well that was a lot of use! I'm beginning to wish I hadn't asked, now.

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

[Leo Lichtman]

Well that was a lot of use! I'm beginning to wish I hadn't asked, now.
^^^^^^^^^^^^^^^
Which one of you wrote the letter to "Car Talk," objecting to their
reference to the "third half of the show?"

[Blair P. Houghton]

Brian Wax > wrote:
>As far as gyroscopic goes, the spinning mass of the wheels adds a great deal
>of stability. That is why many of the after market wheels are pounds lighter
>and the more exotic motorcycles have much lighter wheels. The lighter the
>wheel, the easier it is to change direction. This also has a big effect on
>the suspension characteristics.

But what I've seen (the book by the Aprilia engineers)
says that the gyroscopic effect is supposed to *aid*
turning, not *oppose* it.

I believe what you seem to say, that we don't want so much
gyroscopic effect.

The bike geometry makes it inherently stable while it's
rolling, and the gyroscopic effect hampers controllability.

>short wheel bases and steeper steering angles. These bikes turn well but are
>much more nervous at speed. I had to put steering dampeners on both bikes.
>While accelerating out of turns, the front wheel would shake back and forth
>violently.

Makes sense. Like a shopping-cart wheel, which has trail but no rake.

This is a situation where the gyro effect would be a good thing.

One other thing to note is that with intended precession of a gyroscope
often there is unintended nutation because the forces are not always
balanced.

If nutation were a strong effect (and it's usually more
noticeable than the precession in gyroscopic systems
responding to imperfectly applied torques) then turning
a motorcycle would always involve high wobble amplitudes,
and we'd all notice.

--Blair
"It's falling...with style."