MPG with 31's

[00Classic]

I have been wanting to lift my XJ and run 31's. Now that gas has jumped nearly $1 in two days i am worried about mpg. I am getting 22-23 with stock 3.73 gears and 225/70R16 tires. What are you guys getting mpg wise with larger tires. Once again this is a daily driver so mpg is still kinda important.

Thanks,

 

[Bowzer]

Ya shoudn't loose more than 3-mpg...

 

[Highmiles]

Read this...
http://go.jeep-xj.info/HowtoSpeedoGears.htm#chart

Then decide. You will lose MPG with larger tires mostly due to added roll resistance and gearing pushing you out of the optimal RPM for fuel efficiency.

I doubt anyone can tell you exactly how much due to different driving styles and the fact that your odometer will be slightly off, so you'll have to correct for that before you calculate MPG.

 

[00Classic]

Thanks for the input.

Highmiles, great link. That is a very helpful tool.

 

[WB9YZU]

I have been wanting to lift my XJ and run 31's. Now that gas has jumped nearly $1 in two days i am worried about mpg. I am getting 22-23 with stock 3.73 gears and 225/70R16 tires. What are you guys getting mpg wise with larger tires. Once again this is a daily driver so mpg is still kinda important.

Thanks,

Stock 3.73 gears? In a post 86 unit?

Anyway, not much. Your speedo will be about 7 or 8% too slow though.
,Ron

 

[dmillion]

Stock 3.73 gears? In a post 86 unit?

Yeah, I noticed that, too. In an '00 (which is what I'm assuming your Jeep is, given your name, 00classic) your stock gears would be 3.55 with an automatic transmission and 3.07 with a manual. That's it. No other gears came stock, so if you really have 3.73 gears in yours then they've been swapped in at some point in the past.

 

[VegasAnthony]

Ive heard 373'scoming stock never seen one though

 

[muduck18]

factory towing package? thats the rumors I heard. i don't know though I have never seen it either...

 

[langer1]

Some members have reported getting better MPG, where you drive and how you drive will make the differance. Running the speed limit on flat long roads your mileage can go up. In hill country it will go down. Heavy on the peddle it will go down.

 

[dmillion]

factory towing package?

Nope. Not in an '00. The tow package included deeper gearing in the earlier years, but in an '00 there were only two possible gearsets that came stock: 3.55 with the auto and 3.07 with the manual. That's it.

And with either of the stock gearsets, when you swap to 31" tires your gas mileage will get worse. I don't know exactly what it will be, but I guarantee it will get worse.

 

[JeepXJ93]

not sure about MPG but i had an 00 classic as well and the stock wheels were 16", then i changed to 15" and 31's, stock i averaged about 250miles per tank and then on the 31's i went down to around 225mi. per tank.

 

[mikeny59]

I've been running 31's w/auto and 3.55's on a '98 classic for about 55k (8.25).

Even with the added benefit of the 25% mpg increase with synthetic oil :jester:, and living on Long Island, NY, flatter than prolly any other part of NYS, and 59mph (I hate tickets), mileage is dismal, pathetic, shameful, etc...

Thank God I work 2.3 miles from where I live.

God, I wish I had the time to throw in those 4.10's I bought three years ago...

Mike...

 

[learjets]

I get 19 to 19.5 Highway with a 1994 3 inch lift, BFG AT 31-10.5x15, 4.0ltr, Auto, and 3.55 gears.
It's a 1994 XJ with 231,000 mile that has been kept up (2nd motor, K&N filter, newer O2 sensor, Alignment, etc......). Mileage dropped about 2 to 2 1/2 MPG after lift tires and 4x4 conversion.

 

[XJ Eric]

I've been running 31's w/auto and 3.55's on a '98 classic for about 55k (8.25).

Even with the added benefit of the 25% mpg increase with synthetic oil :jester:, and living on Long Island, NY, flatter than prolly any other part of NYS, and 59mph (I hate tickets), mileage is dismal, pathetic, shameful, etc...

Thank God I work 2.3 miles from where I live.

God, I wish I had the time to throw in those 4.10's I bought three years ago...

Mike...

Thats good to hear. I'm about to go to 31 inch Mickey Thompsons. the same gearing as yours. Other than mileage falling off how bad was your power loss?
Oh and, if you ever think about getting rid of those gears....
Other guys?