Do I Need To Recalibrate My Speedometer

[daveor]

I just got rid of the factory rags and put some new tires on my 2008 z71 4x4 silverado. the old tires were 265/65/18,, the new ones are 265/70/18, they seem to be taller and my gas mileage went down, haven't done any checking to see if the mph was right yet, but thinking that is why the mpg has gone down. The mpg is from the readout on the dash. thanks, DAve

[Zembonez]

Your new tires are 1 inch taller or 3.3% larger. 70 MPH indicated would mean you are actually running 72.31 MPH. As long as you are OK with that, I'd leave it. Just realize on those stretches of highway that are 70 MPH speed limit to allow for the difference. At around town speeds, the difference is so small as to not be worth worrying over.