"Patrick, you're the tire man, so I'll ask ya this..
I run a set of General Grabber A/T's... is 120mph too
fast for them? Can you explain how the rating systems
works? i.e. rated by top speed intermitant or
continuous? What does the industry mean by
continuous?"
The sidewall of the tire should have the size on it, followed by the
"load index" rating. This rating is a 2 digit # and then a letter. The
# designates a certain weight carrying capability, the letter designates
the speed rating of the tire. The speed rating of the tire is a
measurement of a couple of things-top sustained speed, braking
capabilities, and cornering capabilities. Going to a higher rated tire
increases your braking performance, makes lane changes quicker, faster
on off ramps, etc. Some people say "Well, why do I want a 130 mph
tire-I never drive that fast?" To have the other benefits. If you were
on the autobahn and got pulled over by a Weinerkopfen and you were
driving faster than the speed rating on the tires, you'd get busted.
Getting back to your questions- I'd be hesistant about going 120 mph
for more than maybe a quick burst with an A/T style tire. The tread
blocks are larger and squirm around much more at higher speeds than an
H/L or higher speed rated tire. A few A/T styles carry an "S" rating,
yours may not have any rating at all. The rating system does not
dictate a maximum static speed, but gives a dynamic rating-continuous
sustained speed. An "S" rated tire can be driven at 112 mph continually
and it will hold up. The same tire would be expected to overheat/blow
out/fly apart if you drove a constant 120 mph. T-rated is 118 mph,
H-130 mph, V-up to 149, Z-149+, W-up to 186mph.
A quick note-how often does everyone check their tire pressure? Most
truck tires are supposed to be increased up to 10psi more if you sustain
highway speeds of 75 mph or more. The tires should at least be
increased up to their maximum inflation pressure if you cannot inflate
them up to 10 psi. The load index/speed rating doesnt do you a hill of
beans if you blow out a tire at 90 mph because you havent check the air
in it in 3 months, and you only had 22 psi in it and didnt know it. I
highly suggest that you think about the last time you checked the air
pressure before you blast down the highway at 95mph or race the guy in
the next lane.
More on tires-today I attended a Firestone Ride-and-Drive seminar at
Pimlico race track in Baltimore. We drove 4.6L Mustangs shod with Eagle
GA "H" rated tires, then drove Firestone Firehawk SH30's to see the wet
weather improvements. Then we did a slalom course race after the tires
were replaced by "Z"-rated Firehawk SZ50's. Your's truly ran the
hottest lap at 24.98 seconds and took himself home a nice Firestone
racing jacket!!!
Patrick
Firestone in Baltimore
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:14:52 EDT