I just upgraded my Jeep Tires from 235/75/15 to 31/10.5/15.

Am I going faster or slower than my speedometer reads?

Am I putting on more or less miles than my odometer reads?

I don't quite understand your question. You went from 235's to 31"? Is the 235 your old tread width? What is the 31"?

If you went wider and your aspec ratio stayed the same, then your new tires are actually taller. For any given RPM your wheels will be going slower, therefore both your speedo and odemeter will read low.

If you got new rims then I would have to know the old tire's width/aspect ratio/rim size and same for the new tire in order to give you the answer.

The 235 tires are probably 235x70 or 75. The 31's are definately taller, so your speedometer will show you going slower than you actually are.

sorry, more specifically:

OLD TIRE 235/75/15

NEW TIRE 31/10.5/15

thanks