odometer is off??

[97_Danger_Ranger]

put a 2 inch suspension lift and 31's and my speedo reads slow. my odometer is off now correct? same with the trip? how do i calculate actual miles on my trip so i can get a rough estamite of the mpg i get?

 

[smithae]

edit: wrong topic.

 

[strvger]

i went from the original 27.5 tires (195/75x15) to 31.5 tires (215/85x16) and at the same time, went form 3.45 gears to 4.56 gears. my speedometer is off nearly 20mph at 60 reading 77mph. and my odometer is off buy about 2 tenths per mile. i use my tach for freeway cruising so the speedo isn't much of an issue for me. around town, i just keep up with traffic and no problems there either. as for gas mileage, i just do the math. use the mile markers and your watch on the freeway for correct speed. when you fill up, you know the distance from point A to point B, so just calculate the gallons used for those miles and you're there.
little calculator makes it rather easy and close enough for my purposes, but that's just me.

 

[koda6966]

Guess.

 

[Surrey]

Or you could do the math for the change in speedo.

Simply calculate the circumference of both tires, and divide them.
Your 31s should be around 97.35 inches, while 225/75r15 are about 88.85 inches, so your new tires are about 1.096 times the size of your old ones, or just shy of 10% change in speedo/odo