With my tire size (205/45 on 16" wheels) my speedometer is 5mph fast. Which also means higher rpms. which means low mpg, no much I am sure, but mentally I know it is something.

For example, I am cruising 70, really doing 65. RPMS are at 3500, when they should be at 3100ish. 80 @ 4000 is really 75@3500ish, etc...

Ford, GM, Chevy and some Toyotas have aftermarket equipment to plug into the OBDII and can adjust for tire size changes. I have yet to see anything for our vehicles.

Anyone have suggestions? Dealer won't do it.

 

205/50/16 tire will correct it.

 

And cause more rubbing and has nothing to do with speedometer recalibrating.

 

i had no issues running that size on my xa with coilovers

 

there is no way to recalibrate the spedo.. you can move the needles to get a truer reading of your mph, or go back to the proper size tire / wheel combo, or live with the issue, knowing your rims and tires are pimp... there is always a trade off when it comes to pimp looking $hit...
If the dealer could recalibrate they would, but they have no way to do it..

 

buy scangageII and use that as your speedo

 

^ what he said. Use any GPS to establish accurate speed, and the ScanGauge has capability to + or - its reading to match GPS. Presto--your Scangauge now shows accurate MPH with current wheel/tire setup.

If you use a different wheel/tire setup for winter (like I do) simply repeat the GPS/ScanGauge calibration for the NEW setup. Again, use the ScanGauge as your speedo, since it will show true MPH.

 

None of these help, except the it cannot be done answer.

I can use my TomTom if I wanted and I already know I am 5mph slow.

The problem is the rpms. The rpms don't match the actual speed so I am actual spinning the motor faster thus using more fuel.

 

the RPMS has NOTHING to do with the speedo because the engine is running faster because wheel / tire combo is smaller diamater than stock........... you have effectively changed your gear ratio