ok all you OG's, let the n00b's try this one.

what exactly does the speed rating mean???

 

i know! i know!

 

Speed ratings are determined on a 67" flywheel in a test lab. Tires are run in ten minute speed steps (initial speed determined by rating being attempted) with speed being increased 10 kph for each step until failure.

SPEED SYMBOL..............................SPEED CATEGORY
Q................................................. .............99 MPH
R................................................. ............106
S................................................. ............112
T................................................. ............118
U................................................. ...........124
H................................................. ...........130
V................................................. ...........149
W................................................. ..........168
Y................................................. ............186


Z Rated tires are considered "Open Ended Category" where the tire must match the speed capability of the vehicle it is to be sold with (above 149mph).

Failures are usually due to heat-buildup related issues, resulting in mechanical separation of components.

Don't confuse time on a web board with knowledge

Ferd
(Noobie with Integras, oldie with tires)

 

also,the tire must be able to maintain its rated speed for at least 2 hours before failure.

 

Hmmm. According to SAE 1561 and the ECE European spec (don't know that spec number offhand), the tire only needs to pass through that speed step to pass that requirement. We test several steps beyond that for safety purposes, but the specs say nothing about 2 hours.

Ferd

 

so its needs not to come apart at that speed and it passes the test? there is not minimum time or anything?

 

Well, with high speed testing, it's not accurate to compare lab results with real world performance. the lab test is much more severe.

The unit pressures on the tire footprint are more concentrated on a 67" flywheel than on the flat ground. And the temperature effects (the big tire killer here) are MUCH greater in a room with no cooling air blowing past the tire.

If you enjoy sustained running at triple digit speeds, my best advice is "don't". But if your gonna do it anyways, your best bet is getting the highest speed rating you can afford, and keep an eye on your air pressure.

Of course, these are my own personal opinions, and not those of my employer (yada, yada, yada).

 

I won't say that since it hasnt happend to me it must not be possible, but how dangerous would it to to cruise for 4 hours at 120 in a teg down to LA or something? I've done it twice now and the average speed is probably 110 or so. I'm running Z rated tires and am very carefull about the tire pressures I run. I'm suprised there is any aprehension about it. I figured it was a very safe bet if you had a properly designed tire and air pressure.

 

I don't mean to get anyone worked up or concerned here, I just have a tendency to hedge my comments, since large tire companies make good lawsuit targets. We're constantly being cautioned about what we say and how we say it. You're not paranoid if they really ARE out to get you, eh?

"Speaking for myself", you shouldn't have any problems if you stay with speed rated tires, keep them in good shape.

 

i would be intrested to know what temps tire integrity goes down