nwapache said:
There is no upside to changing to a 15" wheel, it will throw your speedo/odo off, and look pretty goofy to boot. I wouldn't recommend it.
That's not true at all. First off, as long as you match the correct tire size with the wheel diameter, the speedometer will remain as accurate as it would with a set of stock 245/45/17's on 17x8” wheels.
Example:
245/45/17 = 25.68" (652.27mm) Stock
275/50/15 = 25.82" (655.82mm) Rear
245/55/15 = 25.61" (650.49mm) Front.
Between all three tire sizes, there is less than 5mm difference in height going from largest to smallest, with the 275/45/17's only being less than 2.25mm taller than stock. Bottom line, he's not going to see a change in his speedometer what so ever and by staggering the tire sizes and he'll even get a bit of a "raked" look to go with it, which is far from “goofy” looking.
Secondly, the tall side wall may not be of any benefit to handling, but it's a big plus for drag racing. Tall side walls will absorb more of the initial "shock" when coming off the line and are easier to hook up as a result. I’ll admit the advantage with regular radials in comparison to say a Drag Radial or true Slick is minimal, but it’s there just the same.
The only reason 17" and 18" drag radials are made at all is because owners want to either clear big brakes or keep the same size wheel all the way around for looks.