Quote:
Originally Posted by Tireman9
I am not aware of where the table is and test requirements are for the various Speed Symbol letters in FMVSS 119, 120 or 139. Could you educate us please.It is my understandnig that the speed rating was added in response to FTC "anti-dumping" tariffs imposed on non-speed rated tires a couple years ago. IMO the speed ratings seem a bit arbitrary and some appear to possibly be unrealistic.
SAE has speed test specifically for passenger tires. You might review that test requirement and let us know if you feel that is reliable to predict use of a tire that has it's load calculated based on 65 mph speed limit.
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NHTSA is not going to allow speed letters on a tire's sidewall without some form of certification from their manufacturers. Here's the short version.
"Speed ratings are determined through laboratory tests. Although this is an over simplification of the actual test procedure, essentially a tire is pressed against a large diameter metal drum to simulate its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10-minute increments) until the tire’s required speed has been met, or the tire fails."