Again, check out the speed rating on the tires in question. On Tire
Rack's competition tire site, EVERY G-FORCE LISTED HAS A Z RATING!!!!
Also every Hoosier radial, every Kuhmo of at least 15", and every A032
Yoko of at least 16". So again, how can we say that a Z rating carries a
guaranty of good tread life?
You've said that any racer knows that a soft compound can't stand up to
the heat. A couple of years ago at the Daytona 24 hour race, I walked by
the Yokohama trailer and watched them truing tires for the Momo Ferrari.
I picked up some of the shavings, and that summer set a piece on the
street. Over the afternoon it melted in the sunlight enough to flatten
into the pavement! Yet this soft rubber stood up to two or three hours
of abuse, hard braking, heavy acceleration, multi-G cornering, and 180+
speeds on the banking. Granted, this is not a DOT-rated tire, but you
can't tell us that soft compounds can't handle speed.
While writing this, it just hit me where John and I look at this
differently. The speed rating is not a rating of how a tire resists
heat! It's a rating of how fast the tire can go and maintain its
temperature rating (A, B, or C). Like I said before, the speed rating
shows how well it dissipates heat or resists heat buildup. A Z-rated
tire with an A temperature rating doing 175 MPH is NOT a hot tire. The A
temp rating means it runs cooler than a B or C tire, even at its rated
speed. A Z rating is not an expectation of resistance to high
temperatures, it's a demonstrated ability to stay cool at high speed. If
it can stay cool, you can use softer rubber on the tread.
Still, tread temperature is a measure of road friction (i.e. sliding),
not tire construction. An overheated tread is one that has been abused
by wheelspin, lockup, excessive slip angles, whatever. Speed rating
doesn't have anything to do with that.
Dixie Region Probe GT