If I move up to 17in wheels, will my speedometer be off?

I have 16's now, but if I get 17's will they mess with my speedometer?

Thanks,
Frank

If you match the outside diameter of the new 17" tires to the outside diameter of the old 16" tires, there will be no affect on the speedometer.

Example.... all of these have the same outside diameter:

245/50-16
275/40-17
315/35-17

Well, right now I have 235/55-16 on it

you should still be only about 1.5% different on your speedo by switching to one of the tires listed.

not enough to worry about

Consider these:

235/55-16 = 26.17" (stock)
255/45-17 = 26.04" (1/3 MPH high @ 60 MPH)
285/40-17 = 25.98" (1/2 MPH high @ 60 MPH)

275/40-17 = 25.66" (1.2 MPH high at 60 MPH)

275/40/17 is the most common size tire on a fbody with 17 inch wheels.