Re: [ST] for Matt and Richard - tire width & cornering

[Thomas Emberson <thomas@xxxxxxxxxxxxxxxx>]

Heyer, Matthew A. wrote:

> Good information.  I still believe that in response to the initial post
> ("I didn't realize a narrower rear tyre improves handling.  Maybe that
> explains why 125's and 250's can carry more corner speed than the
> diesels."), the reason the lighter bikes "carry more cornering speed
> than a liter class bike" is the weight.  There is less weight being
> pulled out (the centrifugal force) and thus less force acting on the
> tire at the same speed as a heavier mass/bike.  Thus, a higher speed can
> be held to bring the tire up to its traction threshold.

As far as pure Physics, if the material is not deformable, then traction 
is proportional to weight over surface area. That is, more surface area, 
means less weight on the given surface area, thus same amount of overall 
traction.

If we removed the deformable and material limitation of the tire, a 
1000lbs bike would be able to hold the same speed as a 100 lbs bike. 
Same with dragsters, if it where no for the tires deforming and other 
wear characteristics of a tire, a 1" wide tire would provide as much
as the 30" wide monsters.

BUT, the rub comes in as rubber is only so strong, that is the rubber 
can only handle so much stress before it warms and liquefies. Some of 
which is good and designed in, but too much would obviously result in 
unacceptable wear.

This is why you have the 385mm wide tire on the back of a Viper, you 
need to distribute the stress over a wide area of rubber, not for 
traction per'se, but for material considerations.

Thus larger bike, you need more rubber to spread the force over. I am 
sure Rossi could get *a single* great lap out of a 120mm wide rear made 
of the same rubber, but the tire would be completely toast going into 
the second.

> You are correct in that the tire differential (and the physics of any
> front-steer machine, in which the rear wheel follows) causes the
> differing arc lengths and the understeer (from the differing arc lengths
> and the fact that the power is being applied at the rear tire - e.g.
> front-wheel and rear-wheal drive cars)

Yeah, but cars lean the wrong way :-)

cheers,
Tom

- -- 
Thomas Emberson


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