itsmeagain5789

i upgraded from 31x10.50 long trails to 32x11.50 bfg mud terrain. just wondering if anyone knows how to get my new mpg. i think u have to add something, but i am NO math wizz, so i have no idea. let me know if you know what i have to add or subtract to miles on odo. thanks

garrett1478

do you mean mph?

mpg is gallons/miles..... i dont think anyone but you will know that.

Elkaholic

If you mean MPH use this, just type in your original size and new size and your golden.

http://www.discounttire.com/dtcs/infoTireMath.dos

edit: oops that might not work exactly sorry

wjwerdna

was soooooooo about to post that link

except that its only for metric sizes, he'll have to convert them, or input random numbers until the overall diameters are equivalent

wjwerdna

once you input your tire sizes and such, scroll down and put speed at "100 mph" it will say something like actual of "107.25" mph, so you take your miles travelled of say 212 and multiply by 107.25% or 1.0725 of course those are my numbers

wjwerdna

actually thinking about that again... its a linear math ratio, so its an easy calculation, find the exact diameter of new tire, and exact diameter of old

me: new=285-75-16 (32.83") old=265-70-16 (30.61")
you: new=32" old=31"

then take new tire diameter divided by old

me: 32.83/30.61 = 1.072525
you: 32/31=1.0323

meaning your speedo is reading 3.23% faster than you are actually going
so to find actual mileage, take odometer reading and multiply by 1.0323 to find actual, to find actual speed do same, if your speedo says 70, you are going 72.3 mph...

(i dont know if 31's are exactly 31, or 33's are 33", there are several factors such as wear and air pressure that affect the diameter used, maybe check wheel manufacturers for actual diameter)

itsmeagain5789

yea, thats exactly what i needed to know, thanks alot Andrew

wjwerdna

no prob

Etype R

The best way to figure it out for your truck, is to get a hold of a GPS. Either buy one or barrow one, and take a few long trips with it. Record your odometer readings along with the GPS.

Now take the miles from your GPS and divide them by the miles from your Odometer. Write this number down, and use it when calculating your milage with your new tires. Just multiply your odometer readings with this number.

With my truck, I simply multiply my odometer readings by 1.13.