i notcied a 5mph difference not just in an app but also in one of those highway radars.. What gives? Engine seems off too with the rpm.. I thought I calibrated the 33s with a flashpaq but i guess not? Any suggestions?

 

The inputed tire size is larger then what you actually have. Don't rely what is printed on the sidewall.

Use a tape measure and re-measure your tires. Generally I find that they're smaller then listed.

Use this information to re-calibrate your computer

 

What Rod wrote above. I've found the quick way to do it is to measure from the ground to the top of the tire shoulder where it makes a sharp break into the tire tread. Typically that's an inch or more smaller than the expected tire size. The accurate way to measure is to mark a spot on the ground and on the tire where it contacts the ground. Then drive forward until the tire mark reaches the ground after one revolution. Measure from the tire mark back to the first mark (on the ground). Divide by Pi. That is your actual tire size. Just for reference, my "35 inch" Duratracs read accurately on the speedometer when the ProCal is set to 33.25".

 

This ^

 

i dont know why but as bad as this sound since its conplicated I was actually able to do it and now all is well lol.. Thank you all