so with the wide knowledge and digging ability of Senior members i have found this nifty calculator that helps you figure out tire size and speed change....

http://www.net-comber.com/tirecalc.html?d2=++27.99

but does any one have one that does odometer adjust for running bigger tires?

Pardon my mathematical naivety, but wouldn't it be the same ratio? If, say there's a 10% difference in speed, wouldn't it equate to a 10% difference in mileage also? i.e. add 10% mileage.

yea, you need to find the percent change.

 

you can use this calc:

http://www.subarubrat.com/Calc.htm

 

punch in your old tire diameter, new tire diameter, and 50mph, and then calculate the percentage difference.

 

 

for example. I found that an EA82 on 215/75r15 tires is 10mph off at 50mph, or 20%. and there's you're conversion, add 20% to your odo number.

And for the calculator challenged, if you wanted to add 10% to your milage, just punch in your milage in a calculator and multiply by 1.10.

 

If you wanted to do 20%, just multiply by 1.20 and etc...