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Unread 03-07-2013, 11:43 AM   #16
mdm
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I've got a little throw-away commuter car that gets 32 MPG. It also doesn't eat through it's little tires anywhere close to as fast as my rig's 35" tires disappear. My stroker also demands premium fuel at a rate of about 13.5 MPG. Significantly lower fuel costs and longer lasting cheaper tires was pretty much a no-brainer decision for me.

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Unread 03-07-2013, 12:30 PM   #17
NonRubicon
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Quote:
Originally Posted by jaxonroberts View Post
So what yall are saying is that modifications like exhausts, air intakes, and programming chips are a waste of time??
Exhaust, intakes and chips are usually done in order to gain more HP and torque. Some chip tunings might be able to increase MPG by forcing a leaner mixture, but with the brick-like aerodynamics of a Wrangler you probably won't see much change.

I think the general consensus on JF is that you won't see anything significant to be worth your time and money, if your are considering the aforementioned mods to improve MPG. You are of course free to give any of these a shot, but don't be disappointed if you fail to get the MPG boost you want.

While different vehicles have different optimum speeds for max economy, once above 50 mph fuel consumption usually increases rapidly for most vehicles.
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Unread 03-09-2013, 10:24 AM   #18
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What size tires and gears are you running?
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Unread 03-09-2013, 11:51 AM   #19
jaxonroberts
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3.73 gears and 32's.
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Unread 03-10-2013, 07:10 AM   #20
Evildriver-3
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Originally Posted by mdm View Post
The Myth Busters test with the pickup and the tailgate is a completely different from most of our Jeeps. A pickup has better overall aerodynamics than a TJ, esp. a lifted TJ with larger tires.

You are making the same mistake mythbusters did, you don't have aero issues at 55 mph, pretty much below 75 mph the aero drag isn't a problem.

Aero has no major effect until 75 mph.

Too bad mythbusters never did that test right as per what people really drive at.

Jeeps with big tires major issues are the tires weight, no one looks at tire weight when they buy them and most buy tires for DD jeeps for the 2 times they leave pavement in 365 days of use.
Having to keep 4 75lb tires moving vs 4 30 lb tires are huge at the mpg area.
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Unread 03-10-2013, 07:22 AM   #21
Steve01WJ
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Quote:
Originally Posted by jaxonroberts
I already drive it easy I always let off the gas early and accelerate slowly. I plan on keeping the Jeep for a good long time so I think that any kind of upgrades will help in the long run.
Simple, if you are worried about mpg....go buy a Prius.

My jeep gets about 10mpg and I love it!

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Unread 03-10-2013, 07:25 AM   #22
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Quote:
Originally Posted by mdm View Post
I've got a little throw-away commuter car that gets 32 MPG. It also doesn't eat through it's little tires anywhere close to as fast as my rig's 35" tires disappear. My stroker also demands premium fuel at a rate of about 13.5 MPG. Significantly lower fuel costs and longer lasting cheaper tires was pretty much a no-brainer decision for me.
This^^ makes sense.
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Unread 03-10-2013, 09:04 AM   #23
jaxonroberts
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Quote:
Originally Posted by Steve01WJ View Post

Simple, if you are worried about mpg....go buy a Prius.

My jeep gets about 10mpg and I love it!

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I love my Jeep more than the next guy. This is my second tj I don't need a great gas mileage vehicle. I just want to see if there is any room for improvement. I'm a college student who pays my own tuition with a full-time job and I commute 60 miles a day four days a week. That's why I started this thread to get information, not to get told I need to buy a Prius.
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Unread 03-10-2013, 09:06 AM   #24
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Quote:
Originally Posted by jaxonroberts View Post
I love my Jeep more than the next guy. This is my second tj I don't need a great gas mileage vehicle. I just want to see if there is any room for improvement. I'm a college student who pays my own tuition with a full-time job and I commute 60 miles a day four days a week. That's why I started this thread to get information, not to get told I need to buy a Prius.
Other than good driving habits and keeping the maintenance up, there are no silver bullets to improve the mileage.
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Unread 03-10-2013, 10:42 AM   #25
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Originally Posted by Evildriver-3 View Post
You are making the same mistake mythbusters did, you don't have aero issues at 55 mph, pretty much below 75 mph the aero drag isn't a problem.

Aero has no major effect until 75 mph.

Too bad mythbusters never did that test right as per what people really drive at.

Jeeps with big tires major issues are the tires weight, no one looks at tire weight when they buy them and most buy tires for DD jeeps for the 2 times they leave pavement in 365 days of use.
Having to keep 4 75lb tires moving vs 4 30 lb tires are huge at the mpg area.
While I agree that tire weight is an issue, isn't it more when it comes to stop and go? Over coming inertia is what kills mileage. Once cruising if you are properly geared I believe less of an issue.

Completely disagree as to aerodynamics at least as it relates to TJs.
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Unread 03-11-2013, 11:50 PM   #26
JustinStrife
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Maybe drop in a SBC?
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Unread 03-18-2013, 07:03 AM   #27
Evildriver-3
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Quote:
Originally Posted by biffgnar View Post
While I agree that tire weight is an issue, isn't it more when it comes to stop and go? Over coming inertia is what kills mileage. Once cruising if you are properly geared I believe less of an issue.

Completely disagree as to aerodynamics at least as it relates to TJs.
The gearing is what helps the stop and go and get the mpg up in that area by making less work for the motor to get to speed, weight is weight and will always take more power to maintain more weight than less weight.
The gearing makes the acceleration easier and at speed it still has the same weight on it, in the driveline the loss of weight in pounds is very important and greatly effects mpg, where carrying weight you need larger amounts of weight to have differences

You can disagree with the aero all you want, it is a fact if you aren't going past the major area the aero drag isn't the problem, as witnessed in the myth busters segments, aero doesn't have special effects on a TJ at 55 mph over another vehicle, now at 80 mph it does have a different effect on tj then it would grand cherokee, now we have a aero related mpg issue.
My Power Ram at 65 mph gets better mpg than the op's jeep, in fact most of the people posting here are less than the CC mpg, the CC has more area than the tj.
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Unread 03-18-2013, 08:11 AM   #28
mdm
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For you folks that believe aerodynamics don't have an effect until you reach 75 MPH, try carrying a sheet of plywood across the wind. It's amazing how much trouble you will have if you try carrying it with the flat of the sheet facing a 10 MPH wind. As you tip the sheet to a position more horizontal you will have less trouble. Compare that vertical sheet of plywood, the horizontal sheet, a TJ, and a typical passenger car. The TJ is much more like the vertical sheet of plywood. When you look at a vehicle rounded corners, curved windshields, the front of the tires covered by more of the body, less air space between the road and the vehicle all these things have a great impact on the amount of drag felt by the vehicle. Drag doesn't start at 75 MPH. It starts as soon as the vehicle starts moving into an apparent wind and increases with speed. The increase in drag isn't linear; it increases with the square of speed. This does mean that you experience much more of an increase in drag when you go from 70 to 75 MPH than you will experience when you go from 50 to 55 MPH. However, to say that aerodynamic drag isn't an impact on fuel consumption until you reach 75 MPH in a CJ/YJ/TJ/JK type of vehicle is foolish.

Frontal area and rolling friction are the major contributors to the mix. The greater the frontal area and rolling friction, the more power is required to move the vehicle which means more fuel consumption. The frontal area of our rigs is much like that vertical sheet of plywood. We tend to like large diameter, wide, high friction tires.
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Unread 03-18-2013, 10:34 AM   #29
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Then why do the mythbusters experience no mpg effects at speeds below 70, why does my cc which has more frontal and overall area get better mpg than the little cj?
Why does mpg show a huge difference at 70 plus and none below that, seems a uncovered bed below that and lower than 55 has no aero effect , comparing a sheet of plywood to a vehicle with multiple steps breaking the air is a horrible comparison. You are wanting to believe the overall shape as one plane, aero doesn't work like that.
My cc with 5 Hella 4000 on the roof gets better than 14 mpg, I have more frontal, more overall area
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Unread 03-18-2013, 11:40 AM   #30
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http://en.m.wikipedia.org/wiki/Drag_coefficient

Also, the force required to overcome drag increases exponentially as speed increases.

What's the real mpg difference between a 2wd and 4wd JK?

The major factors concerning tires are the torque required to accelerate a greater mass, and the aero drag on it.

On two optimal condition tanks of gas (avg 55-60mpg), I got over 17mpg highway with my LJ. City only average is 13-14. Mixed conditions are usually 14-16. For every 5mph I go over 60, I lose 1mpg.
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