My Rubicon Unlimited 2006 is now getting 23.8 mpg on the freeway with 33" tires. - JeepForum.com
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post #1 of 107 Old 06-26-2008, 02:50 PM Thread Starter
CB3
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My Rubicon Unlimited 2006 is now getting 23.8 mpg on the freeway with 33" tires.

Traveling at 58 mph in 3rd gear (auto tranny - OD off since not regeared yet).

Have 33 X 10.5 R15 BFG ATs that I run at 24 psi cold pressure as determined by chalk test by myself and confired by local tire store that used a formula to determine best tire pressure. Their formula said 25 psi, but my chalk test says 24 psi. So I went with chalk test and run 24 psi.

I did several mods each aimed at better gas mileage. All worked to varying extents and contributed varying amounts to improving gas mileage from the 16.5 freeway mpg that I started at to the 23.8 mpg I'm getting now.

I'd like to do a write up that describes each mod I did and how much each mod improved the gas mileage.

I did each mod one mod at a time, then retested gas mileage after each mod. So I know how much each mod matters.

Also, I lifted the Jeep 3" during the gas mileage mods and testing, and still improved gas mileage a lot from other mods.

I'm very happy. My next mod will be an E85 mod.

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post #2 of 107 Old 06-26-2008, 02:53 PM
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so, uh, what did you do?
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post #3 of 107 Old 06-26-2008, 02:57 PM
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post #4 of 107 Old 06-26-2008, 02:58 PM
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What a tease
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post #5 of 107 Old 06-26-2008, 03:01 PM Thread Starter
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As soon as I get approval to submit a write up here, I will. I've never submitted one before. So I'm not sure how to do that.

I need to retest my city gas mileage this week so I know how much that has improved after latest mod (wheels/tires). Then I'll be ready to submit a write up.

For the moment, here is a list of mods.

High efficiency air filter (forgot brand name, but I'll see what it is) my mechanic sold it to me.

Synthetic Motor Oil - Mobil One 10/30 High Mileage (even though my Jeep is low mileage I wanted the better additive package of the HM oil)

Electric Engine Cooling Fan (Flex-a-lite kit for Wrangler)

New wheels and tires. Went from Moab 16 X 8 to American Racing 15 X 8 with 4.5 BS (aluminum) and tires went from Cooper ST 285/75R16 to BFG AT 33 X 10.5 R15 AT. I had looked for the lightest aluminum 15 X 8 wheels I could find that have adequate strength and suitable backspacing.
Some at this forum criticized me for wanting to save pounds on wheel weight and tire weight, with them saying it wouldn't matter much - if at all. Likewise about me wanting narrower tires. It does matter a lot. Rotating mass (drive train, tires, wheels) matters 10 times more than mass that's part of frame or body. Heck, I've also got way better acceleration and braking now too, and a much softer ride due to less unsprung weight and load C tires on 15" rims.
Each mod helped to some extent, but the much lighter wheels and tires helped the most, and I assume the tire being 1" narrower and having AT tread also helped, and it's load range C instead of D (C is lighter).

It's getting better highway gas mileage now than my XJ used to.

I'm not even regeared yet. I think once I'm regeared, I might get even better gas mileage. I might get 25 mpg from her yet.

Note: since I'm not regeared yet, my highway mileage tests were conducted in 3rd gear (OD off - auto tranny) and I got 23.8 mpg. I hope to do better once I'm regeared. Maybe 25+ mpg.

Next mod, E85 conversion kit (sold at NAPA for $400).

Last edited by CB3; 06-26-2008 at 03:11 PM.
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post #6 of 107 Old 06-26-2008, 03:01 PM
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sorry man, but this thread is completely worthless w/o explanation. btw, 1 psi WILL CHANGE IMMEDIATELY WHEN THE TEMPERATURE CHANGES.

EDIT
I see you tried.

So do you think the money you spent in goodies will offset the cost of gas milage?

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post #7 of 107 Old 06-26-2008, 03:02 PM
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replied while i was typing :P
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post #8 of 107 Old 06-26-2008, 03:04 PM
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Quote:
Originally Posted by CB3 View Post
As soon as I get approval to submit a write up here, I will. I've never submitted one before. So I'm not sure how to do that.
You don't need anyone's permission. Just post it up.
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post #9 of 107 Old 06-26-2008, 03:11 PM
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Originally Posted by thejafe View Post
You don't need anyone's permission. Just post it up.
Now!

lol 10 char

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post #10 of 107 Old 06-26-2008, 03:13 PM Thread Starter
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When I do an official write up later, I will list how much improvement came from each mod for city and highway gas mileage.

FYI - it's still a capable offroad rig. In fact, I like it better offroad now because it rides way smoother. It's much better onroad now with way more acceleration and better braking, also has a higher top speed going up local mountain passes.
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post #11 of 107 Old 06-26-2008, 03:17 PM
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i'm very interested to see the write up for a few reasons - I run an LJ, and I've wanted an electric fan for a while, especially since I avoid mud like the plague, and don't do water crossings that much. Already have the air filter and Mobil-1 covered....have you done any other mods?

Also with regard to the fan - which model specifically are you using, and EXACTLY what wiring/relay system are you using to activate the fan and at what temp.


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post #12 of 107 Old 06-26-2008, 03:24 PM
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post #13 of 107 Old 06-26-2008, 03:27 PM
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Quote:
Originally Posted by CB3 View Post
As soon as I get approval to submit a write up here, I will. I've never submitted one before. So I'm not sure how to do that.....
You have my approval. Now just start typing.

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post #14 of 107 Old 06-26-2008, 03:27 PM Thread Starter
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sorry man, but this thread is completely worthless w/o explanation. btw, 1 psi WILL CHANGE IMMEDIATELY WHEN THE TEMPERATURE CHANGES.

EDIT
I see you tried.

So do you think the money you spent in goodies will offset the cost of gas milage?
I meant morning cold pressure before driving. Yes, you are correct that tire pressure changes a lot with temp. That's why I only check in morning before driving. More consistant that way.

Yes, the money I spent will be repaid in gas savings on some of the mods, but not others.

Most of the improvment came (in hindsight after testing) from the change in wheels and tires. Half of that cost will be recouped when I sell my old wheels/tires I have now, which I will have no problem doing since 16 X 8 rims are the fad. Also, my used tires and rims are a more expensive model (being 16") so that even used they will sell for enough to help pay for my new 15" rims and tires. I calculated the difference in gas mileage and how much I drive will pay for the other half the cost of rims and tires within 8 months at the amount I drive at current gas costs. Gas costs keep rising. So if gas goes up, I recoup my mod costs faster. i.e. - as gas costs rise, I'll be even happier I made the mods.

Now aside from the tires and wheels, will the other mods pay for themselves? The high flow air cleaner will because it was cheap ($50 and gains enough gas mileage to be well worth it, plus more power too).

The other mods (synthetic motor oil and electric fan) will never pay for themselves in gas mileage alone. However, they offer other side benefits like less engine wear with synthetic oil. The electric cooling fan lets my engine warm up much faster and that keeps the oil noticeably cleaner. At 4K miles (my normal mileage time to change oil), my engine oil still looked clean and new even though I do mostly city driving! So I didn't change it yet. It doesn't need it. I'm sure my plugs and valves are cleaner too - since engine warmup is very fast. Also, with the electric fan I did notice a slight improvment in engine power at full throttle going up mountain passes.

So the tires, wheels, and air filter will pay for themselves in gas savings alone, but also offer other benefits.

The synthetic oil and electric engine cooling fan will never pay for themselves in gas savings alone because they don't improve the gas mileage very much in relation to the cost of those mods.

However, synthetic oil and electric engine cooling fan offer several side benefits in addition to a slight gas savings. Synthetic oil reduces engine wear. Cleaner oil, plugs, valves due to much faster engine warmups, especially in winter. So the synthetic oil and electric fan are not worth doing just for gas savings, but I think they might beworth doing for reasons related to reduced engine wear and slightly more power - and the slight gas mileage improvement they offer is a bonus.

One thought I've had is that the 33 x 10.5 R15 tires are great on my LJ Rubi. I think some 33 X 9.5 R15 would be great on a TJ or XJ. In addition to the AT offered by BFG in that size, Les Schwabb sells a hybrid tire made by Dean (Cooper) that is 33 X 9.5 R15.
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post #15 of 107 Old 06-26-2008, 03:38 PM
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Yeah we just switched my girlfriends tj with 33x12.5 on 15x10 13.3mpg to 33x9.5 on 15x7 so far were upto 16.8mpg. Not a bad start we still need to do tune up stuff and fluid changes.
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