Tire Speed Rating Question
I'm posting this here because the speed rating of a tire seems to me to cross all lines/types of vehicles. Reading up on warranty issues/questions just now, I came across the following language ...
Forum Discussion
To understand what it means to be non-speed rated, you need to know what the speed rating means.
An example tire, in original undamaged condition is run under load against a test wheel, under standardized test conditions, at the rating speed, for a limited time period. Last information I've seen, the test period was 30 minutes, the test conditions much less severe with respect to heat, than typical summer highway conditions.
The DOT speed rating requirement came out of a series of tire failure accidents in the muscle car era. If a car is not limited to 85 mph (the magic number on our speedometers that was the first atttempt to fix the problem) then manufacturer has to install original equipment tires speed rated for the design top speed of the car.
This does not mean the tires can be driven all day at the speed rating, but does mean when the tires are new they should not come apart when the car is briefly driven at that speed. If the tires are damaged, the cannot be expected to perform as if undamaged, and the warranty language is the tire manufacturer's legal "out" for your expectation that it is safe to drive your car 140 mph because the tires were V rated when new.
It is not correct that unrated tires are rated for 85 mph. Certain classes of unrated tires, such as P-metric passenger car tires, are subject to testing at 85 mph, but that is not the same as a rating. Other types of highway legal tires, like trailer tires, might be tested at lower speeds.
An example tire, in original undamaged condition is run under load against a test wheel, under standardized test conditions, at the rating speed, for a limited time period. Last information I've seen, the test period was 30 minutes, the test conditions much less severe with respect to heat, than typical summer highway conditions.
The DOT speed rating requirement came out of a series of tire failure accidents in the muscle car era. If a car is not limited to 85 mph (the magic number on our speedometers that was the first atttempt to fix the problem) then manufacturer has to install original equipment tires speed rated for the design top speed of the car.
This does not mean the tires can be driven all day at the speed rating, but does mean when the tires are new they should not come apart when the car is briefly driven at that speed. If the tires are damaged, the cannot be expected to perform as if undamaged, and the warranty language is the tire manufacturer's legal "out" for your expectation that it is safe to drive your car 140 mph because the tires were V rated when new.
It is not correct that unrated tires are rated for 85 mph. Certain classes of unrated tires, such as P-metric passenger car tires, are subject to testing at 85 mph, but that is not the same as a rating. Other types of highway legal tires, like trailer tires, might be tested at lower speeds.
