View Full Version : If you put 18" STS rims on a car that had 17" from the factory, does the computer...

12-22-06, 10:38 PM
need to be re-flashed to calibrate the difference in the overall circumference

My car has 17" rims from the factory and they look too small but will going to a larger rim screw up my speedo. i checked the profiles and even though the 18" wheel has a bit lower profile, the overall diameter is still bigger

Also, is anyone running a 19"/18" set up (back/front) and if so, what wheels are you running. i've seen some ACE and some Mille Miglia wheels that would be real nice but not sure what it will do to the computer

Thanks in advance for your thoughts


Benjamin Simon
12-23-06, 12:20 AM
Someone correct me if I am wrong, but often you get a "thiner" tire so that you have more rim. Since the size of the tire does not change, I don't think anything needs to done. But since you have less tire, the ride might be hurt. I would talk to people that have done this before. I would not consider anything over 20s.

12-23-06, 01:38 PM
The diameter of a 255/45/18 is 27.035", the diameter of a 235/50/18 is 27.25" and the diameter of a 235/50/17 is 26.25". I used The Tire Rack website to calculate that. So I would think that a 3/4 to 1 inch difference would through off the speedometer, the odometer, and the gearing.

12-25-06, 10:11 PM
The car's calibrated for 235-50-17s and 255-45-17s. So if you run 18s you should run 235-45-18s in the front and 255-40-18s in the rear. Or thereabouts.

12-29-06, 10:03 PM
It will need to be re-calibrated if you want it to be accurate.