[medicchief]

I am looking to add a short BB or leveling kit to my 07 Unlimited. It is bone stock with 4:10's. I am currently getting 18 MPG (BFG M/T 255/75 17's, auto), with combination driving. What is the average MPG loss as you move up in tire size, to 33's or 35's, with current gears? I don't mean to be lazy, I just hate wasting time (I don't have) searching for an answer.

 

[medicchief]

No one has any input? Thanks.

 

[kjpangus]

I run roughly 17.5 mpg around town with stock 18" wheels and factory ties, my buddy went to 33's with a more aggressive off road tread, (not swampers) and his mileage runs about 16. Part of this is also whether you are a lead foot or not when you start out from a dead stop....

 

[medicchief]

Roger that and thank you. Running 4:10's? Has anyone actually gotten better mileage going from stock 255/75/17's to 33's, running 4:10 gears? Of course speedo would have to be calibrated to know for sure. I have thought about getting a set of the BFG M/T's that come in 255/80/17, they are slightly over 33 inches and are the same width as stock.

 

[JackdUp]

In my short gas consumption test, I just drove 200 miles on Pro Comp 18" wheels and Pro Comp X Terrain 325/60s and I am seeing 12.89, so far.

My first fill I drove 200 miles and filled 15 gallons. I will try this 4 more times averaging 1000 miles and a total of 5 trips to the pump.

I will then divide 1000 miles by the 5 trips combined total of gallons added at the pump to get a better (and hopefully more accurate) mpg estimation.

 

[InfernoGirl]

Did you recal your speedo Jacked up? If not then the readings are not accurate, and neither are your calculations...

 

[arrowhead]

I'm running 4.10 gears and recently switched to larger tires and wheels. My original setup measured 30 1/4" at 28 psi. The new setup measured 32 1/4" at the same pressure. This is with the tires off the jeep. I was averaging 17.5 mpg all around with the original setup and so far I'm doing 18 mpg with the new. My driving style is pretty sedate and there are no hills. The jeep has stock suspension. I factored in the greater distance traveled with the larger diameter tires. Without factoring and using the odometer reading I saw no change.

I measured what I call "rolling diameter" after the new tires were on the jeep. At 28 psi which gives me full tread contact with the ground the diameter dropped to 30 1/2". I wish I had measured the original tires but I didn't. Seat of the pants feel tells me it is about an inch higher than it was like it should be.

 

[JackdUp]

Did you recal your speedo Jacked up? If not then the readings are not accurate, and neither are your calculations...

You are correct that I have not corrected for larger oversized tires. If I am not mistaking, the tire size calculator showed an average of 3 miles difference over a 100 mile distance. Whether that is fact or not is yet to be seen.

For some of you with oversized tires, how can you explain achieving a staggering 17 mpg? Could the inaccurate speedo be mileading the true mpg?

Does a 4-Speed Auto vs 5 or 6-Speed manuals have anything to do with it?