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Old 12-15-2013, 03:48 PM   #1
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How many MPG with 37s and 4.10 on the new JKU/penstar?

Anyone has experience with actual mpg difference when running 37s on the the newer JKU's penstar powerplant? Not withstanding the reasons why or not to run 37s but just a mpg question.

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Old 12-15-2013, 03:57 PM   #2
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I don't run 37's, but I've seen enough posts to safely say "yes, there is loss of fuel economy".

The question isn't really why or why not in terms of running 37's...that is your call. The question people are going to ask is...why ask about fuel economy if you plan on running 37's?

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Old 12-15-2013, 04:03 PM   #3
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Agreed. There is so much cost associated with correctly running 37's that mpg should be of zero concern
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Old 12-15-2013, 04:38 PM   #4
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How many miles should you get on your brakes, and tires?
These types of questions, along with your question, is just impossible to answer accurately!

There are just way to many variables involved, such as where do you drive in town, or highway, flat land, or mountains, how fast, how heavy are you on the foot, winter blend of gas/fuel, or summer blend. As you can see, there is just no accurate way to answer your question.........

Most of us that buy Wranglers, aren't to concerned about fuel mileage, particularly if we are going to install taller and heavier tires, with heavier wheels.
As already mentioned, there will be a negative impact with these options.

Why not 33s, or 35s?
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Old 12-15-2013, 04:57 PM   #5
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I'm guessing 15 - 16 based on my 35s and 4.10s getting 16-17 definitely get the lightest tires you can if looking at 37s; it will matter
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Old 12-15-2013, 05:05 PM   #6
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37's and 3.73's, I get a consistent 15-16.
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Old 12-15-2013, 06:32 PM   #7
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Yall right about the mpg concerns. We all don't drive jeeps for gas milage. I was more or less prodding to see what people feel about it. Most are saying to go 35s and shops are saying to re-gear with 37s.

Now, I believe that my real question should be, "is a 4.10 and 37s a good combo?' Taking costs put of the equation with preference/performance in mind.

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Old 12-15-2013, 06:40 PM   #8
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How many miles should you get on your brakes, and tires? These types of questions, along with your question, is just impossible to answer accurately! There are just way to many variables involved, such as where do you drive in town, or highway, flat land, or mountains, how fast, how heavy are you on the foot, winter blend of gas/fuel, or summer blend. As you can see, there is just no accurate way to answer your question......... Most of us that buy Wranglers, aren't to concerned about fuel mileage, particularly if we are going to install taller and heavier tires, with heavier wheels. As already mentioned, there will be a negative impact with these options. Why not 33s, or 35s?
Great response. I just like the bigger tires on the jku. It just looks better. I would mount 15x37 if possible. But 38s are too big for me. 37s is where I draw the line lol
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Old 12-15-2013, 07:32 PM   #9
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After driving my JKU yesterday while NJ snow storm - I know why I got Wrangler, for sure at this moment you wouldn't care about mpg's I am on stock size Duratrac's, winter is 16mpg local roads and bit better on highways which is rare for my needs. Keep your tires pressured bit more and mpg would be better, however you will read lots of lovers of low pressured tires here ...
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Old 12-15-2013, 07:38 PM   #10
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Just from my experience with JKs, 3.21s & 4.10s with 33s and 35s, I'd figure you would get 9-10 city (city driving takes a bit hit with large tires, no way around it) and around 14-16 highway, 12-14 on hilly terrain like Colorado. The weight of the tire will also be a factor. You will be MUCH happier if you regear to 4.88s. 4.10s on 37s would be pretty damn sluggish.
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Old 12-15-2013, 08:26 PM   #11
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Just from my experience with JKs, 3.21s & 4.10s with 33s and 35s, I'd figure you would get 9-10 city (city driving takes a bit hit with large tires, no way around it) and around 14-16 highway, 12-14 on hilly terrain like Colorado. The weight of the tire will also be a factor. You will be MUCH happier if you regear to 4.88s. 4.10s on 37s would be pretty damn sluggish.
Thanks for the info. It's just that the 4.10 was an option and just hope that it wasn't a wasted option if I needed to regear.
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Old 12-15-2013, 08:33 PM   #12
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37's and 3.73's, I get a consistent 15-16.
Nice. What size rims, 17s?
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Old 12-15-2013, 09:11 PM   #13
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Thanks for the info. It's just that the 4.10 was an option and just hope that it wasn't a wasted option if I needed to regear.
If you are definitely planning on 37s, skip the $500 4.10s, and apply it to the 4.88 regear. Much smarter move.
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Old 12-15-2013, 09:14 PM   #14
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If you are definitely planning on 37s, skip the $500 4.10s, and apply it to the 4.88 regear. Much smarter move.
A bit late. I already ordered. I was keen on 35s until i saw some with 37s. They just looked awesome on the jku.
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Old 12-15-2013, 09:14 PM   #15
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A bit late. I already ordered. I was keen on 35s until i saw some with 37s. They just looked awesome on the jku.
Well, at least the 4.10s will feel more tolerable until you re-gear. You'll probably get 50% of the money back if you sell your 4.10s.
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Old 12-16-2013, 06:36 AM   #16
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I have 37s on 4.56 gears and average 13 or so in hilly areas. You can make due with 4.10 but it won't be ideal but also not completely terrible. The new motor makes so much more power you don't have to gear as deep as the 3.8 guys.
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Old 12-17-2013, 06:05 PM   #17
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I have a 13 2dr Rubi auto, I ran 37's in Colorado for about a month and was getting 15 mpg.
I regeared to 488's and am now getting 16.5 at highway speeds under 75mph after that I tank to about 11 mpg.
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Old 12-18-2013, 06:27 AM   #18
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I am getting around 13 mpg with the 4.10's. (Thats with the wind behind me and going down hill) I even have the flashpaq installed with the 93 octane tune in it. This was the best tune for me to get some of the lost HP and fuel mileage back.
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Old 12-18-2013, 06:45 AM   #19
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My JEEP gets unlimited gas mileage on the highway!!!!! Don't burn any at all!! Can't get any better than that, right!!!!!!

Seriously though.

I know.. I have the super sucky 3.8 and 5.38 gears with a 6 speed manual tranny on GY MT/R 37's w/ steel wheels and Staun internal bead locks....I don't run much highway at all; but I do get around the 14 MPG mark when I do. Just FYI.
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Old 01-01-2014, 02:05 AM   #20
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3.6L, 3,73 gears, 34" Toyo M/T's I usually get around 19 MPG.
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Old 01-01-2014, 01:28 PM   #21
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I average around 13-13.5
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I can get almost 15on the highway.
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Old 01-01-2014, 08:30 PM   #22
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I average around 13-13.5 2014 Rubicon 37s 4.10 auto Flashpaq 87 tune. I can get almost 15on the highway.
Good info. Did the Flashpaq make much different?
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Old 01-01-2014, 09:28 PM   #23
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I ran 37's for 1000mi just to try them out. Wanted to see if the 4.10 gears could turn them. 800mi was on the highway and I was getting 15mpg at 70mph on rolling terrain. I have a 2013 JKUR auto with about 1500lbs of extra weight added. I thought the 4.10's turned the 37's fine and not at all sluggish, it won't chirp the tires by any means - remember it's a jeep. If I want to go fast I'll jump on my s1000rr . Now, if I crawled every other weekend I would put in some 4.56 gears with the 37's. But for now the I will be running 37's soon with my 4.10's.
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Old 01-01-2014, 09:36 PM   #24
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2012 4.88 I run 37" for street 13.5 in town 15 hwy. I run 35" when I off road. I get the same mileage with the 35" on the street.
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Old 01-02-2014, 12:15 AM   #25
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nice. What size rims, 17s?
17"
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Old 01-02-2014, 02:17 AM   #26
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2012 4.88 I run 37" for street 13.5 in town 15 hwy. I run 35" when I off road. I get the same mileage with the 35" on the street.
As stated previously, there are so many variables that it is impossible to project your gas mileage more accurately than +- 20%.

I think Seeuoffroad's number are a good guesstimate because they are only slightly better than I got with 37's with the (12 & 13.5) 3.8 and my MPG was always on the low end of what other posted. Although 4.10 is not the optimal ratio, the 3.6 is noticeably better than the 3.8 and the 4.0 while we are on this topic.
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Old 01-05-2014, 08:52 PM   #27
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As stated previously, there are so many variables that it is impossible to project your gas mileage more accurately than +- 20%. I think Seeuoffroad's number are a good guesstimate because they are only slightly better than I got with 37's with the (12 & 13.5) 3.8 and my MPG was always on the low end of what other posted. Although 4.10 is not the optimal ratio, the 3.6 is noticeably better than the 3.8 and the 4.0 while we are on this topic.
Thanks for the insight. I will be happy with 14. My land rover is supposedly 14/17 so i think it would be an improvement with the new ride. Unfortunately, its not here yet.
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Old 01-26-2014, 01:45 PM   #28
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For city, I'm getting 12.8 avg for the first 100 miles on a brand new stock 2014 jkurx. Thats based on the dash veh info. I would consider it normal driving habits for me which is on the more speedy side but not a lead feet by any means
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Old 01-26-2014, 11:29 PM   #29
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I have a stock 2014 Rubi X with 4.10's and after 1450 miles my overall average is only 13.46. I am amazed at your mileage with 37's, maybe I need to size up and save some gas.
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Old 01-27-2014, 02:24 PM   #30
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I have a stock 2014 Rubi X with 4.10's and after 1450 miles my overall average is only 13.46. I am amazed at your mileage with 37's, maybe I need to size up and save some gas.
No. its literally stock w/stock wheels, auto and 4.10. No mods at all. So, my post was on the bad milage side.

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