NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > Modified Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

Modified Tech Discussion Forum for Tech related discussion for Modified XJ's and MJ's.

Reply
 
Thread Tools Display Modes
  #1  
Old November 23rd, 2007, 19:50
mitsumotors mitsumotors is offline
NAXJA Forum User
 
Join Date: Oct 2007
Location: Winnipeg
Posts: 693
gas mileage

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?
Reply With Quote
  #2  
Old November 23rd, 2007, 20:18
Serveck Serveck is offline
NAXJA Forum User
 
Join Date: May 2007
Location: cumberland, maine
Posts: 156
Re: gas mileage

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.
Reply With Quote
  #3  
Old November 23rd, 2007, 23:01
1sickhick's Avatar
1sickhick 1sickhick is offline
NAXJA Forum User
 
Join Date: Jul 2007
Location: podunk wa.
Posts: 254
Re: gas mileage

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.
Reply With Quote
  #4  
Old November 24th, 2007, 19:51
mitsumotors mitsumotors is offline
NAXJA Forum User
 
Join Date: Oct 2007
Location: Winnipeg
Posts: 693
Re: gas mileage

will i notice a big difference in loss of power, because this engine is already pretty tired.
Reply With Quote
  #5  
Old November 24th, 2007, 20:04
theNAST1EST's Avatar
theNAST1EST theNAST1EST is offline
NAXJA Forum User
 
Join Date: Jul 2006
Location: 4007'02.99" N, 7628'52.99' W
Posts: 513
Re: gas mileage

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

Reply With Quote
  #6  
Old November 25th, 2007, 01:35
tclapp_88's Avatar
tclapp_88 tclapp_88 is offline
NAXJA Forum User
 
Join Date: Oct 2006
Location: IL
Posts: 220
Re: gas mileage

Quote:
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
Reply With Quote
  #7  
Old November 25th, 2007, 06:52
sgtmack's Avatar
sgtmack sgtmack is offline
NAXJA Member
 
Join Date: Oct 2004
Location: Fort Wayne, IN
Posts: 557
Re: gas mileage

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.
__________________
"If there must be trouble, let be in my day, that my child may have peace"
Thomas Paine
Reply With Quote
  #8  
Old November 25th, 2007, 09:58
theNAST1EST's Avatar
theNAST1EST theNAST1EST is offline
NAXJA Forum User
 
Join Date: Jul 2006
Location: 4007'02.99" N, 7628'52.99' W
Posts: 513
Re: gas mileage

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
Reply With Quote
  #9  
Old November 25th, 2007, 12:38
tclapp_88's Avatar
tclapp_88 tclapp_88 is offline
NAXJA Forum User
 
Join Date: Oct 2006
Location: IL
Posts: 220
Re: gas mileage

i didnt replace the speedo gear. but i figured out that its 10% off so i just do math.
Reply With Quote
  #10  
Old November 25th, 2007, 14:00
yossarian19's Avatar
yossarian19 yossarian19 is offline
NAXJA Forum User
 
Join Date: Mar 2007
Location: Grass Valley, CA
Posts: 3,480
Re: gas mileage

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
Reply With Quote
  #11  
Old November 25th, 2007, 15:53
jdurbach's Avatar
jdurbach jdurbach is offline
NAXJA Forum User
 
Join Date: Dec 2006
Location: Centennial
Posts: 163
Re: gas mileage

Nice advice with the big rig drafting always helps I get 20 on a very good day but normally 18-19 on 31"s
Reply With Quote
  #12  
Old November 25th, 2007, 17:39
beatassXJ's Avatar
beatassXJ beatassXJ is offline
NAXJA Forum User
 
Join Date: Oct 2007
Location: Annapolis MD
Posts: 129
Re: gas mileage

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???
Reply With Quote
  #13  
Old November 25th, 2007, 18:35
clunk's Avatar
clunk clunk is offline
NAXJA Forum User
 
Join Date: Apr 2005
Location: West Kootenays, BC (canada)
Posts: 510
Re: gas mileage

Quote:
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.
Reply With Quote
  #14  
Old November 25th, 2007, 19:53
CJ's98XJ's Avatar
CJ's98XJ CJ's98XJ is offline
NAXJA Forum User
 
Join Date: Mar 2007
Location: Where the heck is Moyock, NC?
Posts: 130
Re: gas mileage

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????
Reply With Quote
  #15  
Old November 25th, 2007, 20:50
tayman's Avatar
tayman tayman is offline
NAXJA Forum User
 
Join Date: Nov 2007
Location: Niceville, FL
Posts: 1,424
Re: gas mileage

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.
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
gas mileage? timk578 Modified Tech Discussion 8 April 17th, 2007 21:48
WTB: 97+ LOW MILEAGE XJ in SE ZachMan Wanted: Private Party Only 0 November 20th, 2006 16:12
Mileage Gnat5680 Non-Tech / Off Topic 19 May 14th, 2006 18:58
Bad Mileage MudslinginXJ OEM Tech Discussion 7 July 8th, 2005 14:16
yay for gas mileage!!! DDCxj Non-Tech / Off Topic 8 June 30th, 2004 14:05


All times are GMT -7. The time now is 15:03.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014