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Discussion Starter · #1 ·
First time Jeep owner. Found a great deal from a kid who had dropped all the money into lift and tires, but seemed never used it.
Have a 2007 Jeep Wrangler X 2 door Auto, 3.8L
-Teraflex 3.5" lift
- Nitto Mud Grapplers 35"
- Teraflex Heavy Duty Drive Shaft

I have no idea what gears I have. The owner never re-geared. How do I find out? I'm guessing it's the 3.21 since it's not the Rubicon 4.10.

I'm seeing guys on here saying they get 14-15mpg or higher with mods, lifts, tires, etc.

I'm getting around 10mpg. 11 tops. My DD is 10 miles each way on a freeway to work at 65mph and city driving. Not racing around.

I've read CAI, exhausts, etc have little or no value in MPG gains.
Suggestions? Do I need to look at gears? If I'm running the 3.21 shouldn't that be the best option now for MPG?

I want to add more mods, which will add weight, etc, but the MPG thing is killing me. I have a hard time believing a 7 mpg drop from manfact estimates just from tires, lift, shaft.

Help!

Thanks.
 

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I get about 16.5 average mpg with my 2012 (mostly city driving). I can imagine with a 2007 with a 3.5 inch lift and 35's, the numbers you're getting are pretty accurate. The guys getting 14-15mpg with mods are probably driving 2012's (the gas mileage was improved on the 2012's).
 

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#1 You most likely have 3.73's since it is an auto. But I do believe 4.10's may have been an option for non Rubi's in 2007 only. Email Chrysler you VIN and take can send you a list of the specs that were installed on that vehicle.

#2 Your particular tires are heavy. Really heavy. It is what it is.

#3 If your gear ratio is too (numerically) low, you are actually making it harder on your engine. With the larger (and heavier) wheels, you have changed the final drive ratio. It would like driving around town two gears to high. You are lugging the engine and having to mash to gas to get someplace.

Get ready to spend $1500 to re-gear to at least 4.88's. You may gain some economy back, but you are driving a lifted brick with wide, heavy wheels....so there will be some "suck it up" involved.

Caveat:
This is all coming from someone who has never owned a Wrangler.
 

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Sounds about right for a 2007 with a 3.5" lift and heavy 35s with 3.73 gears. A regearing might get you back a handful of mpgs.
 

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Does Dana/Jeep put a tag on the diff that indicates the ratio inside? Ford does this and has for decades, might be something to check.

Otherwise you and a helper can do a simple check for the ratio. Put the rearend on jack stands so both wheels are off the ground, and mark a line on one of the tires. Then, with the trans in neutral, get underneath and count how many revolutions of the driveshaft it takes before your helper sees one full revolution of the tire. A 3.73 should be roughly 3-3/4 (i.e. 3.75) turns and so on. Easy stuff.
 

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sounds right for stock gears and heavy 35 nittos. Also are you GPS caculating MPG or going by the gauge cluster because the cluster will be wrong unless it been corrected for the larger tires
 

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Discussion Starter · #8 ·
I'll email Chrysler and see how quick they reply with gears or get my brother out in the garage this weekend.

Looking at JK ratio charts now, my 3.21 comment earlier sounds dumb. Apologies. According to the chart attached, if I want DD with OR performance with the auto and 35's, I should be looking at 5.13 or 5.38 gearing, correct?
 

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Discussion Starter · #9 ·
sounds right for stock gears and heavy 35 nittos. Also are you GPS caculating MPG or going by the gauge cluster because the cluster will be wrong unless it been corrected for the larger tires
Doing iphone MPG tracker/calculator. Tried different ones just to make sure. Same results.
 

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Discussion Starter · #10 ·
I also should have listed under the mods -

-18" Pro Comp Rims
-Teraflex 9550 Shocks (obvious with the lift in my mind)
 

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I'll email Chrysler and see how quick they reply with gears or get my brother out in the garage this weekend.

Looking at JK ratio charts now, my 3.21 comment earlier sounds dumb. Apologies. According to the chart attached, if I want DD with OR performance with the auto and 35's, I should be looking at 5.13 or 5.38 gearing, correct?
Right.

And keep in mind that if you measure the actual height of your tires (very likely NOT exactly 35" . . . probably closer to 34"), get on the highway going 70 mph according to a GPS unit, and take a look at your tachometer, you should be able to use that same table to figure out what your current gears are.

They're either 3.73s or 4.10s, neither of which is 5.13 or 5.38.

And honestly, going to 5.13 or 5.38 isn't likely to get you too many mpgs back. You'll probably get better mpgs around town, but worse on the highway. BUT - it will make the jeep much less of a "dog."

For mpg improvements, also consider going to a lighter tire. Last I checked, Nitto doesn't release the weight of their tires, and I expect that's because they're notoriously heavy. If you don't offroad a lot, try moving over to an AT tire like the Goodyear DuraTrac.

Figure $1200 to $2000 for a regearing.

Oh, and I should note that if you look at that chart again, take note of what happens to your RPMs if you try and reduce tire size after you regear. Once you go to 5.38s for example, running a stock tire size again may not be very comfortable. Just fyi.
 

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All post are pretty much nailing it with re-gearing needing to be in your future OR.....get rid of the nittos and definitely get rid of the 18" wheels. Your probably pushing easily over 100lbs per tire with that set up. 35s are heavy, NITTOs are made of concrete, and 18" wheels are heavier than 17s,16s,or15s.
 

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The 35x12.5x18 Nitto Mud Grappler weighs 81 pounds. Add in a 35 pound (give or take, not sure) 18" wheel and you're pushing 116 pounds per corner. That is a lot of weight!

For comparison, my 35x12.5x15 Goodyear MTRw/K weighs 67 pounds and my 15" wheels weigh 24. The BFG KM2's weigh in slightly less than the MTRs, at 61.7 pounds.
 

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I would agree with everyone on here who says to get lighter tires.

I have a similar setup to yours OP... An 08 2door Auto w/ 3.73 gears. 35x12.5 BFG KM2s on 15x8 MB 72 wheels. I am using a superchips flashpaq which in my opinion makes a difference in power and mpg. I am currently getting 17 mpg around town calculated by hand with a correct tripometer/odometer.
 

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I have 61k on my JK and i was getting OK gas mileage but not getting what i was at 20k when the lift and tires went on... this past weekend i changed the plugs and cleaned out the throttle body and i have gone up 1.5-2 mpg!!! i can definitely see a difference!
 

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I have a 2012 JK 4 door stock 18'' wheels no mods yet. I get 14.5 to 15.5 on my commute witch is 50/50 city/highway. On all highway I get 19 mpg. Not so far off!
 

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Try to register with jeep.com and input your VIN. For me at least it brought up all the stock parts included with my Jeep. It has a line for gearing so hopefully you can find out what gears you have that way.
 

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Discussion Starter · #19 ·
I emailed Jeep for the build sheet and they got back to me withing three hours. Not bad. I expected a week.
Turns out mine came with:
DJRS Next Gen. Dana 30 Solid Front Axle
DMFP 4.10 Rear Axle Ratio
DRYP Next Gen. Dana 35 Solid Rear Axle

I guess the questions still remains, should I be re-gearing to the 5.13 or 5.38 (in general) and if so, will I get any MPG back?

Appreciate all the replies. I don't have any plans to remove the wheels right now, since tread is great on all 5 (spare).

I read in another thread the superchips flashpaq can help. I may pull the trigger on that soon. Speaking of which - anyone have any experience with the AEV mod tuner?

I guess hearing the posts from others on here saying they get similar MPG is reassuring in that crappy sort of way. But for the record, I think 7-9mpg difference is THAT far off.

Didn't buy it for a hybrid miles commute, but 10mpg on a V6? I might as well get a muscle car for my daily commute.
 

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Cool...you got 4.10's. I thought there were indeed some 2007's made with 4.10's.

D35 in the rear huh? Bummer

Regear....and/or go to lighter (and smaller) wheels.
 
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