Keep in mind what the actual speed is in increments of 10 MPH. In other words, know what your speed really is at 70, 80....etc MPH I had to do the same thing when driving in Canada (before every car had KPH conversions on the speedometers).

Then, the next time you need tires, either get bigger wheels or stick with tire sizes that allow the overall diameter of each to be the same as the factory diameter.

 

dude.. this still doesnt tell me what your supposed to do if you do have to modify your tire size. is there something that would be changed in the ecu or what...

 

You get your speedo calibrated, but that costs WAY TOO much for what it's worth.

 

i know on old cars theres just a little plastic gear in the trans that you change if you change the tire size or gear ratio in the rear end but they have probably changed that by now cause it was too simple and easy

 

I recently got 17 inch rims and tires to fit, but it seems like the diameter is a little bit bigger than my stock rims/tires because the gap between the wheel and the car is a little smaller. Should I be concerned? Though the shop reassured me that everything is fine?

 

If you get on the Tirerack website, go to the wheels section and enter your year, make, model of your car. When you select a 17-inch wheel, a recommended tire size will be listed. Compare that to what you have. If your aspect ratio is higher (let's say, 45 instead of 40), then your overall diameter is larger than it should be. You can calculate what that should be by using the formula in that website and basing it on the stock wheel and tire size.

 

What size tire did you go from , to? If you have the wrong size tire, you have the wrong size tire. Calibrating the speedo doesn't fix the problem of having the wrong size tire. You'll know that your speed is correct....but, you still have the wrong size tire. This can cause drivabilaty issues, specially if your wheel is a tad wrong as well (offset, etc.)

 

Why would you want to? It just creates more costs and headaches.

Anyway, there are several ways topossibly adjusta speedo/odo, but buying the right tires is usuallycheaper, easier, and better.

You can change the ring and pinionratio in the diff. You can change the tranny ratios. You can change the speedo gear in the tranny/tcase. You can adjust the tire pressure. You can shave the treads. There's probably even a few other ways if you're creative.

 

even if you get low profile tires, aslong as the overal diamet is not drasticly different it wont matter, are speedos arnt that acurate anyways, so when ur speedo is saying 60, you may be going 61 or maby 59 it doesnt mater that much, to only time it would matter is if you were putting truck wheels and tires on a civic, in which case the diameter will be drasticly different.