Help me calculate gas mileage with 35"s...

[K-MU]

Hi there, I tried several tira size calculator but couldnt find one that would give be the right % from my oem BFG 285x70r17 Vs the BFG BT 35x12.5r17...

Ive tried with 3 gas tanks already and got weird results, what I did was just add an extra 5% from the larger tire and got about 10% better gas mileage VS the oem tires, should this be right?

THX in advance

[Contra]

um that doesnt sound right

but lets see pics of the truck with those monsters on it

[kartman]

Im not sure what you are trying to figure out. WIth bigger tires you need to remember that your odometer and speedo will read slow as you will be traveling farther with each revolution of the tire.

[PhatSami]

http://www.izook.com/gearcalc.htm

Here's a good link to some useful tools when trying to figure out that kina stuff.

According to this the 35 is 2.3" taller, thus traveling 7.2" more per revolution. That's a ton more distance considering how many revolutions a tire makes on a tank of gas.

[Mike H.]

I think your tire circumference is now about 6% higher. So if your odometer says you went 300 miles, you actually went 318 miles. Just factor that in when you check your mileage - add 6% to the miles travelled before you divide in your gallons used.

Works the same for speed. Add 6%. If your speedo says 60, you are going about 64.

[CoachBoone]

Can't you just get the speedo recalibrated?

[PhatSami]

yep that's what I got too.

[kartman]

Originally Posted by CoachBoone

Can't you just get the speedo recalibrated?

Not yet, the Hypertech powerpac should allow you to correct for tire and gear changes when it comes out though.

[Mike H.]

Originally Posted by CoachBoone

Can't you just get the speedo recalibrated?

Nope. Nobody makes anything yet, and the dealer can't do anything with them either. It's not like the GM system where other tire sizes can simply be input. That'd be too easy.

[K-MU]

Originally Posted by Mike H.

I think your tire circumference is now about 6% higher. So if your odometer says you went 300 miles, you actually went 318 miles. Just factor that in when you check your mileage - add 6% to the miles travelled before you divide in your gallons used.

Works the same for speed. Add 6%. If your speedo says 60, you are going about 64.

Yea thats exactly what I tought It was right in between 5 or 6%...

How can it be possible that Ive gotten better milage with the 35s?

[bestatchess]

Originally Posted by K-MU

Yea thats exactly what I tought It was right in between 5 or 6%...

How can it be possible that Ive gotten better milage with the 35s?

It is like having a higher (numerically lower) rear axle ratio.

3.357 x 32.7/35 (approx) = 3.136 (closer to the non Big Tow of 2.94)

[54warrior]

I calculated my stock 265/70-18's to be about 32 inches,,, soo 35/32=app. 1.10 %, therefore, for every 100 miles my odometer says, i actually go 110.

someone correct me if i'm wrong... i have been avg. about 14-15 mpg

i also have the non-offroad version with the 3.73's

what does this make my final gear ratio?


found my gear ratio thanks to the http://www.izook.com/gearcalc.htm website

thanks phatsami

[canuk]

Get a hold of a GPS and you can take all the guess work out of it.From stock tires to a set of 35" Toyo M/T my truck was out 6%.

[f00dstamps]

better gas mileage? i'm about to get some 35's. hehe

[Tyltan]

I got worst mileage. I didn't attention how much worst but it is a lot worst with 35".