The SAE speed test which is the one used by tire companies is a 30 minute step speed test. Only need to run 30 min to be rated for 87 or whatever your ST tires are rated for.
The load formula for ST type tires is still based on 65 mph operating speed.
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Retired Tire Design Engineer (40 years). Serve on FMCA Tech Advisory Committee. Write a blog RV Tire Safety. Read THIS post on Why Tires Fail.
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