Does anyone know what the difference would be on the quarter mile with 15" 50 series tires compaired to 17" 40 series tires??? Also is there much of a top speed difference between the 2" size difference? I am tryin to decide on 15x7" rims with 205/50R15 and 17"rims with 205/40ZR17.

 

You won't see any significant difference in acceleration times between those two sizes, assuming you're comparing the same make/model of tire in both cases.

The difference in calculated outer diameter between the two sizes is about .39". To put that figure into perspective, that's less than the diffence in diameter between a set of tires when new, and the same tires when they're worn to the treadwear indicator bars and need to be replaced.

That difference in diameter, in percentage terms, is 1.7 percent. If your top speed is drivetrain-limited (i.e. redline-limited), the smaller diameter 15" tires will have a top speed that's 1.7 percent lower than the 17" tires. (Note that the top speed indicated on the speedometer will be the same in both cases, but the actual top speed will be higher for the 17" tires.) If top speed is a major consideration, you might want to consider 195/55-15 tires for your 15" wheels, as their outer diameter is almost exactly the same as 205/40-17.