Odd RPM

[4x4Hunter]

I figured that putting the stock 235's back on my truck would help for highway gas mileage, however if RPM's are any indication of the gas I am actually getting WORSE mileage and higher RPM's with the 235s than I was with the 33 X 12.5 MT's. Can anyone explain why I would be getting 1500-1800 RPM w/ the MT's and 2000-2200 or so with the stock tires?

 

[mrboyle]

The 235's will increase the RPM of the engine, but your gas mileage will more than likely drop (some) because the engine will not have to work as hard to turn the shorter tires.

 

[Bryce]

When you give those figures for RPM, are you talking about a particular speed? When you change your tires, are you also changing the speedo calibration? If you get a different RPM reading for a particular speed then I would guess that the speedo calibration must have been adjusted accordingly.

Simply looking at your RPM is probably not the best way to determine if your mileage is better or worse. It would be more accurate to divide miles traveled by gallons of gas used.