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Old 05-19-2012, 09:04 PM   #1
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Question Lift..Tires..or Gross Vehicle weight... Which one kills MPG the most?

Keeping it all simple...

Is it the lift... due to change in aerodynamics?

Tires and wheels.. due to rolling weight and wider contact surface?

GRVW..due to aftermarket bumpers, winch, rails, tire carrier and so forth?


Take the average mod...
Say a 2"-2.5" BB lift
32"-33" tires on FACTORY 17" wheels with spacers
and aftermarket front bumper w/ winch and rubi rails and ACE sliders.

on that simple build, what would decrease the MPG? or would it?

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Old 05-19-2012, 09:07 PM   #2
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Getting a jeep kills mpg. Everything you add to it is overkill.

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Old 05-19-2012, 09:11 PM   #3
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I've found these to all be a factor, with weight added on getting the nod. But then I have a lot of weight added. My tires are only 33's, but my lift is 3" - but came up higher, and settled at 4".
That all said, after re-gearing.... I gained back at least 2 mpg. And that's loaded.
AND - loaded with a strong headwind, I gained 4 mpg. Before the re-gear, I'd be at 10 mpg in a strong (read gusting over 30 mph - steady around 20 or so) to 14 'n change mpg in the same conditions. With the same load, if not more.
You didn't specify what year... mine in an '11, auto. Looks like you may have the better tranny of the '12...
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Old 05-19-2012, 09:11 PM   #4
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Quote:
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Getting a jeep kills mpg. Everything you add to it is overkill.


Ok.. MPG by Jeep standard
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Old 05-19-2012, 10:28 PM   #5
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The quick answer is "yes", because it all contributes. The higher your gross weight is, the more energy required to get it moving. Once moving, wind resistance takes over and aerodynamics are the issue. The rolling resistance of the tires and the width of the tires and the contribution of that width to wind resistance all add up.

The conditions you give should definitely detract from mileage, but as already stated, regearing would give some mechanical advantage and may buffer some of the losses.
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Old 05-19-2012, 10:39 PM   #6
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--BINGO--

Regearing gives a subtle payback for all the lift/tires/rack/bumpers/winch

You may not get a substancial return, but you can get at least 15% return of your mileage--based on original gas mileage, but

The cost of regearing far overshadows any increase in mileage !

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Old 05-19-2012, 11:08 PM   #7
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So take what I have listed in the average mod, and the JK is staying equipped w 3.73
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Old 05-19-2012, 11:14 PM   #8
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Yes, you'll lose mpgs due to all of the factors you listed. Probably 2 mpgs or so down from where you are, maybe more if your tires or armor/winch selections are particularly heavy.

Why did you feel it significant to stress you're keeping the factory wheels? They aren't going to do you any favors . . .
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Old 05-19-2012, 11:27 PM   #9
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Quote:
Originally Posted by MTH
Yes, you'll lose mpgs due to all n of the factors you listed. Probably 2 mpgs or so down from where you are, maybe more if your tires or armor/winch selections are particularly.

Why did you feel it significant to stress you're keeping the factory wheels? They aren't going to do you any favors . . .
X2
And dump the factory set for 15or16" lighter wheels better value. But your talking ounces vs dollars. Or looks vs economy
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Old 05-20-2012, 01:01 AM   #10
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Aero effects MPG more than just weight. There are vehicles heavier than the wrangler than get better mpg, but their aero is far better. Air is a cruel mistress.
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Old 05-20-2012, 01:23 AM   #11
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I have to say that the tires and wheels were the biggest contributor. I don't have aftermarket bumpers or any other stuff like that at the moment. I lifted my Jeep 2.5" and through on 35s on the stock alloys. My mileage went from 17-18 to 11-12. The wind resistance plays a good part in the mileage as well, but you have to know the added weight of tires, the rolling resistance created by them, and the amount of power that it takes to rotate them. I you took off your fenders and put 35s on your jeep in stock form, you would probably drop to 13-14 mpgs. Unfortunately, with function comes cost.
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Old 05-20-2012, 03:11 AM   #12
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If I had to rank them:

1st Tires with wider tires causing the worse and weight as a contributing factor
2nd Weight IE heavier bumpers, armor, Winch, And losing air dam with new bumper
3rd Lift - of course lift can move to second if the above weight issues are not too heavy

Then re-gearing can get some % of the effects of weight and rolling resistance back since the engine doesn't have to lug as hard to push the heavier weight down the road

I did my in stages. I got new bumper and winch with evac and oil pan armor first costing about 1.5mpg lose. Next was small lift cost a little over 1/2 mpg. then 285's cost me 2 mpg and then wider 33X12.5 cost an addition .5 over the 285's. Superchips got 1 mpg back at 87 tune and regearing got another 1/2 mpg back.

Note on tires. The heavier narrow 285/70/17 tires cost me 2mpg lose while the wider but lighter 33X12.5X15 cost me 2.5mpg. So wider tires cost more in mpg lose then heavier tires did. Rolling resistance was more a key in mpg lose then unsprung weight
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Old 05-20-2012, 06:53 AM   #13
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I have 32X11.50X15 A/T, can I replace these tires with a 31X10.50X15 without changing rims? I want to narrow my foot print from 11.50 to 8.50 or so.
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Old 05-20-2012, 07:18 AM   #14
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Quote:
Originally Posted by Brad Becker
I have 32X11.50X15 A/T, can I replace these tires with a 31X10.50X15 without changing rims? I want to narrow my foot print from 11.50 to 8.50 or so.
Yes, but your footprint will be 10.50, and you'll have some pretty small looking tires.
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Old 05-20-2012, 01:50 PM   #15
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Quote:
Originally Posted by MTH
Why did you feel it significant to stress you're keeping the factory wheels? They aren't going to do you any favors . . .
I was looking from a view point of upgrading from the GY Sport tires, to say the rubicon BFG MT.

A simple swap
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Old 05-20-2012, 02:53 PM   #16
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It depends on how and where you do most of your driving-

If you spend a lot of time on the highway maintaining steady state operation, rolling resistance and aerodynamics will matter much more than weight.

If you drive mostly stop and go at city speeds the aerodynamics will matter less and your weight, particularly unsprung weight will play a larger role.

For your stated specs, you are using factory wheels and tires, so you will not see much difference there. If you're not going to go for more suspension travel or a tire that requires additional height I'm not sure what the lift is doing, but it's not going to help mileage. You're adding weight with the bumpers and sliders...depending on how you drive, that could be a big difference for you or relatively mild.

Quote:
Originally Posted by JKU.12 View Post
Keeping it all simple...

Is it the lift... due to change in aerodynamics?

Tires and wheels.. due to rolling weight and wider contact surface?

GRVW..due to aftermarket bumpers, winch, rails, tire carrier and so forth?


Take the average mod...
Say a 2"-2.5" BB lift
32"-33" tires on FACTORY 17" wheels with spacers
and aftermarket front bumper w/ winch and rubi rails and ACE sliders.

on that simple build, what would decrease the MPG? or would it?
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Old 05-21-2012, 09:40 PM   #17
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Quote:
Originally Posted by Brad Becker View Post
I have 32X11.50X15 A/T, can I replace these tires with a 31X10.50X15 without changing rims? I want to narrow my foot print from 11.50 to 8.50 or so.
I have a Rubicon 2.50 lift with alloy rims,most of my driving is paved roads,on the farm and deer camp,in the past I have run these BFG A/T 11.50s while in snow off road they run up on snow pack and break through the pack and I get stuck,I thought if I ran a narrow tire I could push through the snow instead...Thanks for all the great information Guy's.
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Old 05-21-2012, 10:05 PM   #18
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I have a Rubicon with a 2.5" lift, running stock 32" tires and spacers. I was told when I added lift to expect mileage to drop to 10mpg on the highway. Happy to report very little change in mileage to date. Planning on going to 35" tire next. I think mileage will suffer then. It's a Jeep not a Prius. Didn't buy it for mileage to start with.
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Old 05-21-2012, 10:43 PM   #19
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Quote:
Originally Posted by jsmithtx
I have a Rubicon with a 2.5" lift, running stock 32" tires and spacers. I was told when I added lift to expect mileage to drop to 10mpg on the highway. Happy to report very little change in mileage to date. Planning on going to 35" tire next. I think mileage will suffer then. It's a Jeep not a Prius. Didn't buy it for mileage to start with.
10 mpgs? That's insane. On stock tires, a 2.5" lift will cost you 1 or 2 highway mpgs tops.
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Old 05-22-2012, 07:52 AM   #20
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Good grief, my '08 Ruby JKUR is lifted/w 33.6" tires/rack/avg GVW 5200 lbs and I get 13mpg-OFF-ROAD IN 4WD/ 16/17 mpg freeway--

No matter what you do to the jeep-EVERYTHING DEPENDS ON TRANNY/ GEARING and DRIVING TECHNIQUE, for gas mileage control, YOU CAN LEAVE THE ENGINE ALONE !

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Old 05-22-2012, 07:55 AM   #21
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I'd say tires and wheels by far. Unsprung weight is your enemy.
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Old 05-22-2012, 09:58 AM   #22
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A significant change in tire size will change mpg more than weight or aerodynamics. I have made many such changes over the years and tire size definitely changed mpg the most.
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Old 05-22-2012, 10:31 AM   #23
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an interesting discussion from the nerds: Drag calculation in 3D, 'virtual wind tunnel'?

My change to same circumference Kelly Safari TRS weighing considerably more and with far more contact patch, cost me about 1.5 MPG compared to OEM Duelers.

No lift, no mods to confuse the MPG change.
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Old 05-22-2012, 10:38 AM   #24
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Of course the mileage test was done for over 1000 miles on the same road/same distance/same speed/same atmospheric conditions/same Barometric pressure--right ?


Quote:
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an interesting discussion from the nerds: Drag calculation in 3D, 'virtual wind tunnel'?

My change to same circumference Kelly Safari TRS weighing considerably more and with far more contact patch, cost me about 1.5 MPG compared to OEM Duelers.

No lift, no mods to confuse the MPG change.
And the mileage was calculated with the same "FULL" tank--right ?

If not, then you just looked at your ECO during the next tank of gas-right?

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Old 05-22-2012, 10:54 AM   #25
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All of the above matters, but I'd say having the shape of 2 offset stacked bricks is 70% of the problem! :-)

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