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gas mileage

mitsumotors

NAXJA Forum User
Location
Winnipeg
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?
 
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.
 
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

:cheers:
 
theNAST1EST said:
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

:cheers:

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
 
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.
 
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
 
i didnt replace the speedo gear. but i figured out that its 10% off so i just do math.
 
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
 
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???
 
yossarian19 said:
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.
 
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????
 
I just recently got 31x10.5's. before that, I was getting like 15.5 miles to the gallon. I did some calculations:geek:, 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.
 
well making sure that your airfilter is clean is a start. A step up is a K&N or similar intake system. Just cleaned my K&N out over thanksgiving and I noticed a 4mpg increase after the cleaning. 13.5 mpg from fort collins to denver and on the way back up to fort collins I got 17.8 with similar traffic conditions
 
Yeah, a tune up will help, no doubt.
Switching to lighter weight rotating gear (wheels, tires, brake rotors?) will help with mileage, as will proper gearing and keeping a light foot on the gas. On a 250 mile trip, with 130 miles in the mountain and hill country of Utah (altitude ~ 3% power loss each 1000 feet, mind you, so I'm running 20% weaker up here) I still get 19 MPG at 80 MPH, WITH 1.5" lift in front.
 
Ive got a K+N in it. put it in bout a year ago, but i'll clean it anyway. I bought it from a neighbor. He bought it from a friend of his and thinks it still has the OEM wires and plugs. It's got 135000 on it and has no major issues. I hopin a tuneup, throttle body spacer and cleaning the K+N will do the trick. It got good milage before the lift. I really don't want to drop it back down and put the old wheels and tires back on till I get a little beater commuter mobile. Any other ideas would be appreciated.
 
sgtmack said:
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.

I get 21-22 hwy on my stock height 99 with 89k miles!
 
Just bought the 2nd XJ last week and has 3" lift with 32's BFG MT's. Average of 17MPG. Keeping a clean air filter in helps. You might consider a throttle body spacer as well. think rusty's offroad a has the kit, so does powerade (sic?). An exhaust kit doesn't seem to help a lot in my experience either. You could also go with the premo spark plugs and the big plug wires. Think NGK does those. Port and polish intake or exhaust, this one makes me nervous on the xj's and doesn't last forever. My favorite right now is the TBS, small power boost and improved gas mileage for fairly cheap.
 
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