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Discussion Starter · #1 ·
I am being a 'DEE DEE DEE' - however I can't seem to figure out the precentage difference between my stock tire size and my new tire size.

Originally, my runner had 225/75 R15's. When I had 31's on it, I would add approximately 10% onto my trip odometer to hand calculate my MPG. Now that I am rolling on 33's, I am not sure what percentage I need to go by.

I have done the MPH and Ratio Calculators on 4LO's site, however I still can't seem to figure this one out!

Anyone have the magic formula??

Thanks, and please forgive my stupidity in advance! :D

John
 

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IF you went from a 225/75/15 (28.3") tire to a 33" tire with out a gear change you divide the new tire size (33) buy the old tire size (28.3) and you get a whole number (1.166). That means that your odometer is off by 16.6%. so when you calc your mileage you multiply your miles buy 1.166 then divide by gallons used.

Example

33/28.3=1.166


300 miles x 1.166 = 349.8

349.8/16 gallons = 21.86 MPG.
 

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Discussion Starter · #4 ·
IF you went from a 225/75/15 (28.3") tire to a 33" tire with out a gear change you divide the new tire size (33) buy the old tire size (28.3) and you get a whole number (1.166). That means that your odometer is off by 16.6%. so when you calc your mileage you multiply your miles buy 1.166 then divide by gallons used.

Example

33/28.3=1.166


300 miles x 1.166 = 349.8

349.8/16 gallons = 21.86 MPG.
Ahhhhh - Cool!! I got the 1.166 answer in my original attempts, however percentage decimal rule of thumb is to move it either left or right two hops (depending on multipying or dividing) and it was the 1 before the decimal point that kept throwing me for a loop.

I knew 116. wasn't right, and I knew .01166 didn't seem right either!

Thanks for the clarification!

Mucho Gracias Mi Amigo!

John
 
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