245s to 265s do you need to calibrate speedo?

Switched stock steel sr5 wheels and tires for sport wheels and tires.

Do I need to calibrate speedo?

 

nope 245/75-16 are basically the same as 265/65-17 for outside diameter

 

Tire size calc shows sport tire .3 more mph at 65 what is the math to add that to my mileage to figure accurate mpg

Over 400 miles to a tank that's gonna add up no?

 

.3 mph is well within accuracy specs for any speedo, don't loose any sleep over it...

 

You'll see more error in either size tire from brand new to well-worn - my p245-75/16 dunlops lost a full inch in diameter when replaced, and they weren't down to the wear bars yet.

I recalibrate my ScanGauge for distance about every 10k miles, due to wear and change in tire diameter, which changes revolutions per mile, and what the speedometer/odometer reports.