For those of you driving the stock rims and tires. If you drive with a tom tom or alike and compare the speed with the odometer what is the read out? Is it dead on or is the odometer optimistic?
I am trying to compare with stock so I can figure out what my actual mpg is since I run 37's and have an unadjusted odometer

 

If I am going 71-72 on my speedometer, my Tom Tom says 70. So I set my destination and recorded the mileage to see if I was driving more then the speedometer was recording since its off a couple of mph, on a 54 mile trip there might have been 1/10 of a mile difference. I have 265/75/16's on my H3.