140 rating equals 8-15 K tire life? Anything's possible, but that probably would involve a whole lot of "hammering" -- say, some track work.
The tread wear ratings are set by the manufacturers, and 100 is supposed to equal 20,000 miles. In other words, the OEM 18" RE040s are rated by Bridgestone to last 28 K.
Bridgestone -- and anybody -- would tell you that there is a wide range, depending on use/abuse. In setting the 140, though, they are not supposed to give you a rating that only works when you putter along at the double nickel. They rate the tires for 168 mph, and design them to go on a car with the capacity to generate high braking and cornering loads (moderate acceleration loads), which they know will be bought and driven by people who will use that capacity.
I don't know how honest Bridgestone is in its rating, but they should be saying that a person who drives vigorously on the road (I don't think they factor in track use, and they shouldn't have to for this purpose) will get 28 K, on average.
In a few years, we'll see what really happens.
Sunlight Silver auto, touring package, black cloth, aluminum pedals, Pirelli 245-40s on stock wheels, license LSTFLNG