Tire/mileage calculator?

[Bigcheck1]

I replaced my original size tire (265x65x17) on my Xterra with a BFG All Terrains (265x70x17). I have yet to find a calculator to tell how much my speedo and mileage is off. This thing has always gotten terrible gas mileage, but it can't be this bad. If anybody knows of a good calculator, let me know.

 

[Blee1099]

I replaced my original size tire (265x65x17) on my Xterra with a BFG All Terrains (265x70x17). I have yet to find a calculator to tell how much my speedo and mileage is off. This thing has always gotten terrible gas mileage, but it can't be this bad. If anybody knows of a good calculator, let me know.

265/65/17 = 30.6" tire
265/70/17 = 31.6" tire

at 55 MPH, your doing 56.8
at 65 your doing 67.1

Dead Link Removed for speed calculations.
Dead Link Removed for tire size conversion

 

[carlover]

Not to hijack your thread but i have a similar ? and none of those calculators seems to give me the info i need lol. I had 3.27's with the stock size tires, 27in i believe. I now have 33's (well actually closer to 32) but i swapped out a complete rear end with 4.10's. Now since the new rear end has the speed sensor calibrated for the 4.10's should my speedo be pretty close to accurate?

 

[Bigcheck1]

Blee, thanks.

Any idea how to tell about my mileage? Is it 5% off? Any way to tell? I was not a math major......

 

[Blee1099]

Its less than that.. My math says 3.25% increase