TIre Safety

Tires have a temperature rating - A, B, etc. Are there any recommendations regarding maximum speed at which to drive a given tire temperature rating at varying ambient temperature? I live in Kuwait. Our fleet has 4x4’s with “B” temperature rating, but we routinely see ambient temps above 40 C in the summer. I am wondering if we should be recommending to drivers to not drive beyond certain maximum velocities with these tires when temperatures exceed certain limits.

Tires also have speed ratings. Unless your drivers routinely drive their trucks over 100 MPH, T, S, or H rated tires should be OK as long as they are properly inflated.

If they do drive over 100mph, then tires are a minor issue regarding driver safety, you have more to worry about…

If your drivers are going fast enough, in 4WD vehicles, to worry about the temperature rating of their tires you have much larger problems on your hands.

As long as the tires are properly inflated they will be fine. How fast are you driving these vehicles?

A temperature rating of “B” means the tires are rated for safe use between 100 and 115 mph. Tell your drivers to stay under 100 mph.

Tires don’t have temperature ratings. For an understanding of what codes tires DO have, visit http://en.wikipedia.org/wiki/Tire_code.

Tire pressure is the most important. Check it frequently, and of course, keep the speed down to a safe level.

Our drivers are supposed to drive no more than 75 mph. I was hoping that there might a be “rule of thumb” to indicate a de-rating of the tire’s maximum velocity if it had a treadware/temperature/traction rating of “B” versus “A” when the tire is in use in ambient temperatures exceeding 40 degrees centrigrade (about 105 degrees farenheit.)Doesn’t sound like there is such a “rule of thumb” for de-rating max. velocity with increased ambeint temp.

I am asking about this issue, because we have had several motor vehicle crashes which seem to involve a tire blowing out, relatively new tires so age/wear was ruled out. Our leased sedans have “A” tread/traction/temp rating … have been told we can’t get “A” rating for tires on our leased 4x4’s.

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Are there situations where the actual speed a tire is capable of withstanding different than the test would indicate?

The answer is: “Yes!”

Normally, new tires are tested. John Baldwin tested some older, but unused tires and found that the speed capability had deteriorated 2 steps. Ref: J. M. Baldwin, “Field Aging of Tires, Part 1” presented at a meeting of the Fall, 2003 meeting of the American Chemical Society - Rubber Division

This makes sense against the backdrop that rubber degrades over time.

What about the speed capability of tires that are inflated to a lower pressure, but properly loaded for that pressure?

John Baldwin (again) also tested this and found a 2 step drop there as well. This was also not an exhaustive study and more work is needed. Ref: J. M. Baldwin, “High Speed Testing Of Tires and the Use of Constant Deflection,” presented at a meeting of the Tire Society, Akron, OH, September 23-24, 2003.

The speed capability of a tire could be quite less than the speed rating. If you add up what is known, you could be looking at a 6 step drop - and those are just the issues that are known!


There is a rule of thumb that says that if you are experiencing 3 to 5 psi pressure build up during operation, then that is good. More than 5 psi indicates a need for action - slower speeds, less loads, more inflation pressure, larger tires, etc.

Do a study of the pressure buildup and that will tell you a lot of what you need to do.