More info here too, citing a 7,200 mile test loop in Texas.Hm.. Good point. This is what I found here:
UTQG treadwear rating means that the manufacturer took the tires to a testing facility, put it on a test vehicle and measured it against a standard tire with a 100 treadwear rating. If a tire is rated 300, that means it is expected to wear three times faster than the 100-UTQG rated tire.
How does that translate to miles? It doesn’t.
"If the test tire is expected to last as long as the reference tire, it receives a UTQG Treadwear grade of 100. If it is expected to last twice as long, it would receive a grade of 200. 300 means it is expected to last three times as long, and so on."