on 10/3/00 7:40 AM, Mike Oberle at [EMAIL PROTECTED] wrote:
> Here is a quote from an article:
>
> "First of all, it helps to know the difference between a radial and a bias
> ply tire. To understand the difference, it helps to know a little bit about
> tire construction.
To add a bit to Mike's article, the real danger in mixing bias-ply and
radial tires on any vehicle, not just two-wheeled ones, is the fundamental
difference in the dynamic lateral behavior of the types. To put it simply,
radial tires are made to flex from side to side while maintaining the
contact patch's contact with the road surface. Bias-ply tires are not made
to flex the same way.
To draw a word picture, imagine the wheel (and, for that matter, the rest of
the vehicle) in a radial tire shifting sideways under cornering load, the
sidewall bending to take up the slack, and the contact patch staying more or
less flat on the road as the vehicle turns. (easier to picture with a car
than a bike, but the idea's the same) In other words, the inside of the tire
(next to the wheel) moves fairly readily while the outside part of the tire
(next to the road) stays stuck. The stability of the contact patch and the
relative flexibility of the sidewalls are what make radials effective. They
resist heat because the flex that's built in doesn't generate as much as a
bias-ply design.
A bias ply tire, on the other hand, is built to resist the side-to-side
motion for as long as possible, keeping the whole tire moving as a unit, and
it rolls up the contact patch on the inside of the tire until it finally
releases. This is not all bad, and until fairly recently most racing tires
were bias ply rather than radials.
BUT, as you can see, the two types behave really differently under cornering
loads and interact in fairly unpredictable ways. If you set up a bike with
one bias ply and one radial, the tendency of the radial to move sideways and
the bias ply to resist can cause real problems when one or the other
releases at the limit - what should have been a simple controllable slide
becomes a disastrous high or low side instead.
Most of the time you won't notice this effect unless you're paying
attention, but at the limit it'll bite you badly. Don't mix 'em.
best,
Sat Tara
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