I suspect that differing tread widths [and even height] with different manufacturers is common, even when sizes stare you in the face as identical. A vehicle not in my sigline [mainly because it was my wife's car first-off, not mine -- I just got to drive it once in a while] was a really nice white 1993 manual Celica all-trac in almost new condition -- it had a sort of weird pale blue leather interior that I didn't find very appealing, but it had a great stereo w/ CD, the transmission was excellent, and with the supercharger it really went like stink. I had never driven a vehicle with a 220kph speedo before, and it could get awfully close to that speed, still stable and predictable -- very quick off the line and very fast overall. Good brakes, too. Yikes. Anyway, it was a wonderful road car with the only problematic thing being an annoying torque wind-up "clunk" from the centre differential when making a slow-speed, full lock turn [and I seem to recall reading somewhere once upon a time that the drive train found its way into the earlier RAV4 line]. But back to the tires -- not surprisingly, the original Michelins wore down fast and needed replacing in short order. I can't remember the size offhand [they were pretty small -- something like 205/45ZR15], but when the new ones were delivered -- with the identical sizing to the ones being replaced -- I was amazed to see that the new tires, not Michelins but something else [can't remember the brand now] were more than a full inch narrower than the stock high-performance ones. And even though the numbers were exactly the same, they were also not quite as tall at regular pressure, either, so the car took on a bit of a peculiar, somewhat stunted "roller-skate" look. It still went fast and was a lot of fun, but with the tire change, for me it lost a bit of its original charm, zap and handling ability -- it eventually found a new owner still shod with the smaller, "shorty" tires. The V8 Sport is, of course, a completely different animal -- but it's still a wonderful thoroughbred in the same spirit as the little white all-trac from years ago. And the Vatiivas seem perfectly suited to it.