I'm trying to figure out my mpg's but I'm not sure if I'm doing it right. First off I have 32" tires and never got the computer reprogrammed for them so my mileage is off. I read a post on here a little while ago that if you upgraded to 31" tires you just take your mileage times .3 and then add that to get the correct mileage. So if thats the case I drove 205miles before filling up. When I filled up I put 15.127 gallons in. So would it be correct to take 205 x .3 = 61.5 So I went 266.5 miles on 15.127 gallons of gas. Then just take 266.5 / 15.127 =17.6mpg ??? This seems a little to good to be true, but is that about right? Am I getting roughly 17mpg?

 

What did you truck come with stock for tire size? 235/75R15 are 29" tires which results in 698revs/mile. A 32" tall tire results in roughly 630revs/mile. A difference of 10.3%. So if you travelled 205 miles with stock calibration, you really travelled 226.1 miles. If you pumped 15.127 gallons of fuel, your mileage was 14.94MPG.

 

I knew it was to good to be true. But I guess 15 isn't to bad. I still plan on getting underdrive pullys and a tune. Also right now I have 3.42 gear. I plan upgrading my rear and having a 4.10 gear. Would the 4.10 give me better city milage but less on the highway?

 

Possibly on the gears. All depends on how you drive. I don't know if I would go to 4.10 gears though... That is a rather large jump. 3.73 gears would probably be better. It all depends on what you are looking to get out of it.

Also, I don't know if I would advise the use of underdrive pulleys if you have any high load electrical items (ie. your lights and your e-fan).

 

I was going to go 3.73, but I think I'm going to jump to a 33" tire this summer. Also as far as the pulleys, I plan on upgrading my alt. and battery before I do the pulleys.

 

You just have to be very careful with U/D pulleys even in some stock applications. You should determine what your max amp draw of all of the aftermarket equipment you have in your truck and select an alternator that has a rated output atleast that much higher than the stock alternator.

 

If you're guaranteed to be going to 33" tires, I'd say go with the 4.10s...

As for UD pullies... Aside from all your accessories spinning slower, most of them are aluminum...

Aluminum slips easier, and also scratches and scores easier than steel, so if you do a lot of 4x4ing you might have some issues with dirt eating the pullies... Though, most likely nothing serious right off the bat, lol.

 

thanks for the tips!