Wheel question

[95mustang_gt]

well im putting 18in rims on with 285/40/18 in the back and 255/40/18 in front.My questin is my mph going to change.If im doing 50 will i really be doing 50?

thanks
Jesse

 

[Joes95GT]

Stock wheels are 225/55/16. 16+2*((.55*22.5)/2.54) = 25.744 inches.

Those wheels are 285/40/18. 18+2*((.40*28.5)/2.54) = 26.796 inches.

You'll be a little bit off, but an inch won't make a big enough difference until around 50 and I believe it's only going to be about 2 MPH off...

Joe