Every now and then somebody posts these conversions but I can't find where they're getting them from. Basically I want to know how to calculate my actual speed and mileage with off size tires.

Specifically I have 4.10s with 30x9.50 tires, but I'd also like to know what the equations are so I can figure it out for other size tires. Right now though, I'm just trying to get a more accurate gas mileage calculation.

Right now I'm reading about 16mpg, but I know I'm getting slightly better than that since my odometer is thrown off by slightly bigger tires.

 

give a man a fish:

http://www.4crawler.com/4x4/4LoCalc.shtml#MetricTire

teach a man to fish:

when you want to search YT, i recommend searching on google instead. YT's info almost always comes up first anyway (because this site rocks). but you can skim google results and you can't skim YT's. (you have to open the threads)
for this, search "tire size calculator" and "gear ratio tire size toyota"

OR, just go to 4crawler.com and look through there FIRST.

good luck,
Tj

 

i got to putzin' around with tire calculators and found this one, which may interest you. it looks like it also calculates ODOMETER ERROR, which is what i think you need to calc. your correct mileage.

http://www.dakota-truck.net/CGI-BIN/TireCalc.cgi

 

Tire rolling circumfrence..
OLD / New.

31x3.14 = 97.34 / 33x3.14 = 103.62 = .93

So you would then take you indicated miles traveled and multiply it by 1.093 and that's your actual miles traveled. You then divide actual miles by number of gallons to fill up. This will get you pretty close to approximate.

 

Where did the 1.093 come from? I think you may have had a math error. I am pretty sure that should be 1.07. And in that calculation multiplying by pi is unnecessary because it cancels. I think it is easier to use the ratio of the tire diameters multiplied by your mileage.

(new tire diameter)/(old tire diameter) x (odometer mileage)

 

Sweet, thanks.

Looks like I'm still getting pretty crappy mileage then. Only really maybe 1mpg better than I thought.

 

You may be more correct.
I was close

 

this one allows you to play with all kinds of numbers...
http://www.grimmjeeper.com/gears.html

probably already found what you need though

 

Thanks OC. I found that one in my searches, but it basically just tells me what my speed is in different gears at different rpms, which is helpful, but doesn't really help with the gas mileage thing.