Rick:
I agree w/Dale-- really excellent analysis of two sources of motorcycle
instability. Thanks.
Russ
"Clay, Dale" wrote:
> WOW Words from a true expert. Thanks for passing that, Rick
>
> Dale C.
>
> -----Original Message-----
> From: Rick Hammond [mailto:r.hammond@sympatico.ca]
> Sent: Monday, December 10, 2001 10:05 AM
> To: land-speed
> Subject: Re: MC-CHASSIS-DESIGN -LSR wheels
>
> Hi All,
> Here is the reply I got off the MC chassis list; check out Tony's site; he
> knows
> his stuff.
> Cheers,
> Rick
>
> Rick asked about;
>
> <<
> The question is whether the added gyroscopic effect of heavy wheels would be
> an
> advantage for a LSR bike, or as with other sorts of competition is it still
> better
> to have light components?
> >>
>
> Cut down on your rotating and unsprung masses as much as possible. The high
> speed will give you all and more of the gyro effect that you need.
>
> A high unsprung mass is good for rider comfort when hitting bumps as it
> forces the tyre to do the work instead of the suspension and so less shock
> reaches the rider. But the price to pay for this is that the tyre suffers
> more and endures much greater load variation. It's much better to wear a
> kidney belt and stick to light wheels.
>
> A high speed weave is regarded as a castor oscillation of the rear part of
> the bike about the steering axis. However, it's effects are not restricted
> to the rear alone, a motorcycle is a highly coupled system and the front is
> affected also. A large part of this front to rear coupling is due to gyro
> effects and so it's a good idea to minimize these as much as possible.
> Motorcycles and bicycles have two inherent modes of wobble / weave
> instability, 1. an oscillation of the front steered assembly about the
> steering axis, normally referred to as wobble, and 2. the rear equivalent as
> mentioned above, known as weave. These instabilities are fundamental to the
> vehicle type but whether they become a problem on any particular bike
> depends on a whole host of factors, damping being an important one. This
> isn't just added steering damping, there are many sources of damping in the
> system anyway ;- tyres, shocks, rider, there is even hysterisis damping in a
> flexing chassis. Too much damping can cause just as many problems as too
> little so adding a steering damper is not necessarily the cure in all cases.
> Tyre damping of the kind known as yaw damping in the car world will probably
> be very different on the salt compared to tarmac and maybe this has a lot to
> do with any increased problems experienced in practice on salt. This is
> just an idea because I don't have the personal experience to say for sure.
>
> Tony Foale.
> Espaqa / Spain
>
> http://www.tonyfoale.com
>
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