question on mpg drop

mudbug660 · April 17, 2005

Did anybody notice a mpg drop when they installed 20's or bigger on their truck. If any of ya'll did what wa ya'll before and after #'s?

98bagsilverado · April 22, 2005

I didn't see a change, but one factor that you have to keep in mind is the diameter of the wheel. The different size wheels will affect your speedometer. I could make it seem that your not going as far as you really did. The other factor is the weight of the larger wheel.

Wingnut · April 22, 2005

Wheel size has absolutely nothing to do with speedometer or odometer calibrations.

The overall diameter (or circumference, if that's how you want to do the math) of the tire is the deciding factor there.

Now, bigger wheels can add to the rolling or unsprung mass which will adversely affect your power and braking abilities. Which is where you would see the mpg drop. The engine has to work harder to turn those heavier wheels.

98bagsilverado · April 23, 2005

Thanks for the clarifications i meant overall tire size when i said wheel size

allenmehrer · July 23, 2005

Don't forget your breaks have to work harder to stop the truck too. Also I think the conversion on wheel weight is like, for every pound you put on the wheels its like having 7 added to the cab. So for example having a tire/wheel combo thats 25 lbs havier a set than stock would be the same as adding 700 lbs to the cab. (25lbsx4sets=100 100x7=700lbs)

Thanks high school math!

Dustin07 · August 4, 2005

I noticed with higher larger tires on same size rims that my trip is off by 10%. meaning, when i check it on the highway mile markers (the one that says speedometer/tripometer check point) I go .9 miles for every one mile i have actually driven.

Does this mean i could roughly add 10% to my total miles driven when figuring my trip?