gas mileage

[mitsumotors]

anyone have a estimate on what i can expect to happen to my gas mileage. i'm going from 235/75-15's to 31/10.5-15's. the actual difference in tire height is only like 2 inches so i'm assuming it won't really be that noticable but what has everyone else seen?

[Serveck]

it all depends on the tire, and what tread, if your going with an A/T, you will get much better mileage than a M/T. but it will decrease by about 10-15% on average.

[1sickhick]

whith my 31x10.5 15 BFG km mt I got 22mpg on an average.91 xj 4.0.whith 33x12.5 15 swamper tsl raidial 17mpg.

[mitsumotors]

will i notice a big difference in loss of power, because this engine is already pretty tired.

[theNAST1EST]

31's on stock gearing will generally keep you around 20 mpg...i run bridgestone a/t's and got 21 mpg on my way home from school

as for power loss, it is what it is, a given...a good tune-up always helps nonetheless

good luck

[tclapp_88]

Originally Posted by theNAST1EST

31's on stock gearing will generally keep you around 20 mpg...i run bridgestone a/t's and got 21 mpg on my way home from school

as for power loss, it is what it is, a given...a good tune-up always helps nonetheless

good luck

wow really??? are you talking highway or town though with that 20? cuz i have 31 mts stock gears and get 15 average in town and 19-20 highway

[sgtmack]

My 99 didn't get 20 on the highway new. Are you guys correcting the odometer for the new tires? Most are getting 17-18 with 31's. Renix engines seem to do a little better. But they are all different, so you might get lucky.

[theNAST1EST]

sorry...that was 21 mpg highway, running at a steady 60-65

no speedo adjustments, 5.5" of lift, 31's on 15" steelies, stock gearing

just set yourself up behind a big rig, and take it easy on the skinny pedal

...oh, and the PA turnpike is no walk in the park

[tclapp_88]

i didnt replace the speedo gear. but i figured out that its 10% off so i just do math.

[yossarian19]

With heavier tires you are going to lose some MPG, with taller tires you are going to lose some power. With stock gears and 30s I notice that I have to drive fast into a long hill or I'll lose 3rd gear (I'm in the mountains of Utah, though) 31x10s on stock gears, you'll notice a good drop in power.
You can help the MPG loss by using alloy wheels instead of steelies - help offset the increase in rotating weight

[jdurbach]

Nice advice with the big rig drafting always helps I get 20 on a very good day but normally 18-19 on 31"s

[beatassXJ]

WOW! you guys are lucky...on 30'' m/ts i get about 14 in town and 17 on the highway. But not much power loss...is there much diff btw 30s and 31s for power/mpg???

[clunk]

Originally Posted by yossarian19

With stock gears and 30s I notice that I have to drive fast into a long hill or I'll lose 3rd gear (I'm in the mountains of Utah, though)

I notice the same with my auto, stock 3.55 gearing and a set of LT235 75R15 all terrains. It doesn't exactly "zip" around like it used to when I bought it with 205 70 R15 passenger highway tires, but then and again it also does alot better offroad, so I accept it as a tradeoff. Because mine is a DD(albeit my daily drive is sometimes only 30km/week) I don't want to sacrifice much highway driveability. I might try a set of 31" BFG AT's after I have lifted it to see how it does, but I can't see myself being happy with the lack of power.

[CJ's98XJ]

Ouch!!!! Ive got a 98 w/RE 3 1/2", 31x10.50's on 15" steelies and dick Cepek FC2's and stock gears. I'm getting about 13 mpg. I'm having a new house built in NC and my commute is gonna be bout 45 minutes. this mileage is gonna kill me. What steps would be good to get some better milage????

[tayman]

I just recently got 31x10.5's. before that, I was getting like 15.5 miles to the gallon. I did some calculations, and figured out that the 31's travel 1.14 miles to the stock's 1.0 miles on the same amount of rotations. I'm still working on gas mileage fot the 31's though, so we'll see where my mileage goes. I'm also working on lifting it this week, so I don't know how that'll effect it.