Again, the speed rating is a measure of the carcass design, not the
tread surface characterstics. Note the previous post from Jay Mitchell
about Z-rated A032s. Tire temperature, for purposes of speed rating is
not tread temperature, it's the heat buildup inside the tire, in the
sidewalls, the belts, the plies, etc. This heat is the result of
internal friction as the tire deforms against the road surface. A faster
tire has to do this at a higher rate, and has to either withstand or
dissipate the heat. Granted, disintigrating is technically a way of
dissipating heat, but not what we're looking for. This is why
higher-speed-rated tires generally have a sturdier build to the carcass.
The softness or firmness of the tread compound (different rubber from
the carcass) has absolutely nothing to do with it. Tread temperature is
pretty much a measure of slip angles, wheelspin, whatever the tire does
besides roll straight, and a Z-rated street-compound tire can be
destroyed in a few runs and never reach 50 MPH. (As I've said in
previous posts on other subjects, don't ask me how I know!)
Walter Fooshee
Dixie Region Probe GT
John Whitling wrote:
> Speed ratings are
> not so arbitrary. Tire design is a constant battle
> of handling and dissapating heat. Soft compounds cannot survive long enough
> at high enough temps to get a Z rating, hence the benifit to using speed
> ratings
> as a measuring stick.
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