Maximum cornering speed

[Zebee Johnstone]

In aus.bicycle on Fri, 26 May 2006 10:43:12 +1000
flyingdutch <[email protected]> wrote:
>
> No, I wasnt, but who knows? he was a friggin mtb(er) (who arent friggin
> by mmere definition but was in this scenario) who decided he would ride

If they were, I duno they'd allow you to televise it....


Zebee
- wondering how you get two people on one of those things.

 

[TimC]

On 2006-05-24, Bleve (aka Bruce)
was almost, but not quite, entirely unlike tea:
> * - here's one of my lads, just after losing the front wheel at Sandown
> at a crit this last summer, and managing to stay upright - it had just
> started to drizzle and a normally very grippy corner, suddenly wasn't :
>
> http://www.aboc.com.au/images/galleries/20051206-sandown/DSCF5949.html
> http://www.aboc.com.au/images/galleries/20051206-sandown/DSCF5950.html

Nice photography!

--
TimC
>Cats are intended to teach us that not everything in nature has a function.
You're saying cats are the opposite of bijectiveness? -- ST in RHOD

 

[TimC]

On 2006-05-25, Tamyka Bell (aka Bruce)
was almost, but not quite, entirely unlike tea:
> flyingdutch wrote:
>>
>> Jono L Wrote:
>> > Tip #1 Always look well around the corner ie. where you want to go, not
>> > in the gutter were you will crash.
>>
>> ..and why? It aint cos you see where you are going (altho it does tend
>> to come in handy)
>> It's cos it shifts you weight, turns your torso/shoulders
>>
>> best way to do emergency avoidance of
>> bolllard/cardoor/collingwood-supporter is by doing thus...
>
> Why do you want to avoid a collingwood supporter?

You don't if your chainring is sitting out in front of you. Aim for
the shins.

--
TimC
I read [.doc files] with "rm". All you lose is the microsoft-specific
font selections, the macro viruses and the luser babblings.
-- Gary "Wolf" Barnes

 

[TimC]

On 2006-05-25, Peter Signorini (aka Bruce)
was almost, but not quite, entirely unlike tea:
>
> "Gemma_k" wrote:
>> you're aware of it. The whole idea of countersteering in a motorcycle is
>> that the gyro effect of the front wheel (and fork) is actually the 'lever'
>> to tilt the rest of the bike behind the steering tube.
>
> Exactly my point. On a bicycle you don't need that help, as your body weight
> is such a large proportion of your total vehicle mass. A small body shift
> will prduce a good tilt.
>
>> Push a spinning
>> wheel one way and it makes a force the opposite direction. Everyone's
>> done
>> it - hold a bicycle wheel by its axle, spin it quick and try to twist the
>> axle...
>
> Try this - spin the wheel, now tilt the wheel over to the left, watch the
> wheel promptly turn left.

Except that the gyroscopic effect clearly does not operate to keep a
bicycle upright, nor change it's handling abilities (presumable same
for a motorbike -- higher speeds at top speed by a factor of a few,
but higher weight by a factor of a few).

Spin the wheel really fast, and note how much force is required to
twist it. Do you really think that force can support your weight?

Now try to build a bike that has two equal weighted wheels rotating in
the opposite direction to the road, at the same speed as the two road
contacting wheels. There will be no diffence in handling. It's not
the gyro effect, it's the countersteering that continually happens.

--
TimC
Skywalker> You are either with me, or you are my enemy.
Only a Sith deals in absolutes. -- Obi Wan Kenobi on George Bush Jnr

 

[Peter Signorini]

"TimC" wrote:

> On 2006-05-25, Peter Signorini (aka Bruce)

>>
>> Try this - spin the wheel, now tilt the wheel over to the left, watch the
>> wheel promptly turn left.
>
> Except that the gyroscopic effect clearly does not operate to keep a
> bicycle upright, nor change it's handling abilities (presumable same
> for a motorbike -- higher speeds at top speed by a factor of a few,
> but higher weight by a factor of a few).
>
> Spin the wheel really fast, and note how much force is required to
> twist it. Do you really think that force can support your weight?
>
> Now try to build a bike that has two equal weighted wheels rotating in
> the opposite direction to the road, at the same speed as the two road
> contacting wheels. There will be no diffence in handling. It's not
> the gyro effect, it's the countersteering that continually happens.

Oh agree very muchly. Countersteering is what keeps you rolling on two
wheels, but I don't agree that a *countersteering action* is the only way to
make an effective turning manoeuvre. My weight shifting will act through
gyroscopic force to turn the bike. Hint: try riding no-hands - can you make
turns by body movement? Of course you can, not so well because you're
sitting too high and can't regulate the turn with your hands, but turn you
will.

Incidentally, spinning your wheel very fast manually is surprisingly 'not
fast'. Once a friend showed me a 95kmh speedo reading from between Lorne and
Anglesea. I thought that's just not possible, he must have rigged it. Tried
to spin my wheel by hand as fast as I could. I got the princely reading of
about 20kmh!! So I guess he either had an erratic pulse from the sensor, or
did 95kmh on the descent into the LH bend coming into Anglesea. There was a
bit of a tailwind, but still soo dangerous.

--
Cheers
Peter

~~~ ~ _@
~~ ~ _- \,
~~ (*)/ (*)

 

[Aeek]

On Fri, 26 May 2006 23:42:28 +1000, "Peter Signorini"
<[email protected]> wrote:

>Incidentally, spinning your wheel very fast manually is surprisingly 'not
>fast'. Once a friend showed me a 95kmh speedo reading from between Lorne and
>Anglesea. I thought that's just not possible, he must have rigged it. Tried
>to spin my wheel by hand as fast as I could. I got the princely reading of
>about 20kmh!! So I guess he either had an erratic pulse from the sensor, or

my two highest readings were
1) rear sensor, I locked my rear wheel braking hard for a hairpin in
traffic
2) front sensor, I was riding slowing on a wet cement path and was
confused which way to go at the Y-fork. Both wheels slid out as I
dithered.
Both reading were 3 figures!

 

[Rory Williams]

Except that the gyroscopic effect clearly does not operate to keep a
bicycle upright, nor change it's handling abilities (presumable same
for a motorbike -- higher speeds at top speed by a factor of a few,
but higher weight by a factor of a few).

Spin the wheel really fast, and note how much force is required to
twist it. Do you really think that force can support your weight?

Now try to build a bike that has two equal weighted wheels rotating in
the opposite direction to the road, at the same speed as the two road
contacting wheels. There will be no diffence in handling. It's not
the gyro effect, it's the countersteering that continually happens.
TimC
Skywalker> You are either with me, or you are my enemy.
Only a Sith deals in absolutes. -- Obi Wan Kenobi on George Bush Jnr

As I understand it, the minimal effect of gyroscoptic force was described in 1970 by Jones DEH(1970)"The stability of the bicycle" Phys. Today 23(4) 34-40.

I have also seen a mathematical model for the countersteering effect in Fajans J (2000)"Steering in bicycles and motorcycles" Am.J. Phys. 68(7) 654-659. (I found this one on the web somewhere and I have a copy)

My physics isn't up to it all. At the time I was looking for an explaination for a rather nasty speed wobble I experienced comming down Olivers Hill one day. It was very nearly one of those "so this is it, we're all going to die" moments.

I've changed a few things since then and I haven't had it again. I supect that the longer stem I was using then slowed my steering response time so I was too late in responding to an instability caused by a shift in the wind while cornering. But I really don't understand it. I had to relax and let it run straight to get control back, then I tensed and it happened again.

I've been a rather tentative descender ever since.

RoryW

 

[rooman]

...snippy...

My physics isn't up to it all. At the time I was looking for an explaination for a rather nasty speed wobble I experienced comming down Olivers Hill one day. It was very nearly one of those "so this is it, we're all going to die" moments.

I've changed a few things since then and I haven't had it again. I supect that the longer stem I was using then slowed my steering response time so I was too late in responding to an instability caused by a shift in the wind while cornering. But I really don't understand it. I had to relax and let it run straight to get control back, then I tensed and it happened again.

I've been a rather tentative descender ever since.

RoryW

Did you have a wobble, known as "shimmey"?

nothing to do with cornering, more likly the resonance through the frame which can build up as a function of a number of things, normally positional, which tranlates as (in four words) "the frame doesnt fit you".

Been there done that, big person too small a frame, too short in wheel base, not enough rigidity in frame and lots of other forces, hence shimmey, wobble, call it what you like, not a pretty feeling , especially when hit by a cross wind at the same time, which is common on Oliver's descents.

You can touch the top bar with a knee to take the resonance out, but it is temporary..

IMHO check out your position and if the frame really does fit you.

 

[Bleve]

rooman wrote:
> Rory Williams Wrote:
> > ...snippy...
> >
> > My physics isn't up to it all. At the time I was looking for an
> > explaination for a rather nasty speed wobble I experienced comming down
> > Olivers Hill one day. It was very nearly one of those "so this is it,
> > we're all going to die" moments.
> >
> > I've changed a few things since then and I haven't had it again. I
> > supect that the longer stem I was using then slowed my steering
> > response time so I was too late in responding to an instability caused
> > by a shift in the wind while cornering. But I really don't understand
> > it. I had to relax and let it run straight to get control back, then I
> > tensed and it happened again.
> >
> > I've been a rather tentative descender ever since.
> >
> > RoryW
> Did you have a wobble, known as "shimmey"?
>
> nothing to do with cornering, more likly the resonance through the
> frame which can build up as a function of a number of things, normally
> positional, which tranlates as (in four words) "the frame doesnt fit
> you".
>
> Been there done that, big person too small a frame, too short in wheel
> base, not enough rigidity in frame and lots of other forces, hence
> shimmey, wobble, call it what you like, not a pretty feeling ,
> especially when hit by a cross wind at the same time, which is common
> on Oliver's descents.

http://www.sheldonbrown.com/brandt/shimmy.html

 

[Rory Williams]

rooman wrote:
> Rory Williams Wrote:
> > ...snippy...
> >
> > My physics isn't up to it all. At the time I was looking for an
> > explaination for a rather nasty speed wobble I experienced comming down
> > Olivers Hill one day. It was very nearly one of those "so this is it,
> > we're all going to die" moments.
> >
> > I've changed a few things since then and I haven't had it again. I
> > supect that the longer stem I was using then slowed my steering
> > response time so I was too late in responding to an instability caused
> > by a shift in the wind while cornering. But I really don't understand
> > it. I had to relax and let it run straight to get control back, then I
> > tensed and it happened again.
> >
> > I've been a rather tentative descender ever since.
> >
> > RoryW
> Did you have a wobble, known as "shimmey"?
>
> nothing to do with cornering, more likly the resonance through the
> frame which can build up as a function of a number of things, normally
> positional, which tranlates as (in four words) "the frame doesnt fit
> you".
>
> Been there done that, big person too small a frame, too short in wheel
> base, not enough rigidity in frame and lots of other forces, hence
> shimmey, wobble, call it what you like, not a pretty feeling ,
> especially when hit by a cross wind at the same time, which is common
> on Oliver's descents.

http://www.sheldonbrown.com/brandt/shimmy.html

Thanks for those thoughts The Jobst article hadn't been published when I was doing my investigations.

My frame "an older" Hillman has a fairly long wheel base, but perhaps it is a bit flexible. While I'm not short (~184cm), At the time I wasn't what I'd call heavy (~67kg)

Even given what is in the Jobst article, I do not think that the change in stem length is incompatible with modifing the effect for a "hands on" wobble. One aspect is a change in the amplitude of the various vibrations that one's hands feed into the front wheel, this might also affect their frequency. The other thing is a forward shift in my mass relative to both wheel. I remember seeing one discussion based around the nature of the front wheel caster effect in relation to the effective centre of mass, which gets shifted according to things like compensating for cross-winds but also the aerodynamics of the rim/wheel. I think the upshot was that you (or the circumstanses) can shift the effective centre of mass to the point where it is forward of the steering axis, which has a detrimental effect on steering stability. I would have to chase this up. Perhaps thsi is another part of the

Only happened the once, and perhaps the particular set of circumstances will never re-occur. Certainly my recovery was based on relaxing and riding it out. I've read the knee on the cross-bar elsewhere, perhaps it's good insurance.

Thanks again

RoryW

 

[Bleve]

Rory Williams wrote:

> > http://www.sheldonbrown.com/brandt/shimmy.html
>
> Thanks for those thoughts The Jobst article hadn't been published when
> I was doing my investigations.

FWIW, I'm not convinced that Jobst is correct. A lot of things can
affect a resonance, not just frame size and flexibility - for example
my very stiff bike, that is definatly not too big for me, gets a shimmy
at 55km/h around the southern bend of the blackburn velodrone - without
fail every time I do a flying 200. It doesn't happen on my (same
geometry, but not quite as stiff, and different stem and seatpost
position - *slightly*) other roady.

Have a read of this book if you get a chance :
"Bicycling Science". It has a very good section on how bikes handle
and how they steer, what makes them feel stable (which isn't
necessarily what makes them actually stable - feel and reality differ
sometimes).

 

[Rory Williams]

Have a read of this book if you get a chance :
"Bicycling Science". It has a very good section on how bikes handle
and how they steer, what makes them feel stable (which isn't
necessarily what makes them actually stable - feel and reality differ
sometimes).

Thanks. Sounds interesting, I must hunt it up.

RoryW