[QUOTE]
Originally posted by lee
[B]Somebody should jump on me and pound away for spouting things that usually turn out to be tales of old and basically incorrect...maybe I'll be lucky this time??
But I always thought speed rating had a lot to do with sidewall rigidity. By that I mean a "Z" tire will contribute less flex to the total system compliance in response to impulse (bumps) than an equal size "H" tire. A side effect would be the amount a tire "rolled over" in spirited cornering, the "Z" rolling less, and therefore maintaining better traction - all else equal of course. It would be this reduced sidewall flex that then reduced temps and therefore allowed higher sustained speeds. Conversely, a lower letter would yield a slightly softer ride at the expense of sustained speed and cornering capability. All this ignores tread design and compound of course.
I thought that the ability to sustain higher speeds by higher rated tires had to do with the overall construction materials & bonding agents used. But I'll concede to anyone who actually knows. I wonder what the belted biased racing tires of 40-50 years ago had that kept 'em from disintegrating at speeds that would embarrass any street legal car of today.
Ron.