Tire circumference and mpg's - Toyota Nation Forum : Toyota Car and Truck Forums

downwind4final · 10-03-2007, 10:32 AM

If I switch from a 215/60/16 to a 225/50/17 revolutions per mile increase by 9 (from ~795 to ~804) and would affect the speedometer by .75 mph. Would this affect gearing enough to noticeably impact gas mileage? This would also inaccurately increase the number of miles on the odo too, correct?

kyle@tirerack · 10-03-2007, 12:43 PM

The formula below will help you determine the new RPM range that the vehicle will run at with the new diameter at different speeds. Just plug in the numbers with diameters and your current rpms at speed for the changes. This is a minimal change and I don't feel that you'll see a dramatic difference either way.

(Original Tire Diameter / New Tire Diameter) X RPM@MPH = New RPM @ actual MPH
This example is for 55 MPH
Example:
(27" / 32.5") x 2400 RPM = 1985 RPM @ 55 mph with new tires.

downwind4final · 10-03-2007, 12:50 PM

Thanks!!

It comes out to ~23 rpm. I don't see that having any effect. It's about the same differece in overall diameter as a new set of tires and an almost worn out set.