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Old 07-24-2013, 08:07 AM   #1
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Question Tire size verse MPG - what can I expect?

I have owned my 07 JKU for a month now and am wanting to change tire size BUT would like to have a feel for what I can expect MPG wise with bigger tires.

Been on the forums long enoigh to know some peoples thoughts on MPG on jeeps BUT I am setting up my jeep for DD and weekend warrior (80/20). I drive 120 miles daily to and from work so MPG is something I have to consider. With that said I not expecting a GODLY MPG I just want to know what kind of MPG I can expect for a given size tire. Right now during the week I am averaging 19.7 and getting 17 - 18 on weekends.

so here is my setup right now: 07 JKU stock, no lift or lvling kit, 4:10 gear, auto, and running 245/75R16's streets.

I really want to run 33's with lvling kit....probably keep stock rims if I go this route.......but been considering running 31X10.5R15's with new rims (Yes I know there are only a select few 15's rims that will fit a JKU). I kind of feel if I run 31's (not much different than what I have now) that I will regret not going to 33's BUT also feel if I run 33's and take a big MPG hit I will regret not getting 31's. The tires I will run will be Goodyear Duratrac.

so my question is what kind of MPG drop can I expect to see if I ran 31's or 33's?

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Old 07-24-2013, 08:30 AM   #2
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Are you sure you have 4.10s? Rubis come stock with 255/75/17 or 32" tires. Your running a 245/75/16 witch is 30.9" and on a different wheel. Sports and Saharas don't have 4.10 gears unless someone regeared it before you bought it but I'm guessing you really have a base sport or sahara instead.

31" tires on a JK won't mean anything bad to your mpg. 32" tires won't change anything. Things become interesting when moving to and above 33" tires. Depends wildly on your driving style and choose of tire.

If your driving 120 miles each day, you need a street tire or light AT. BFG AT or Duratrac no bigger than 33".

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Old 07-24-2013, 08:34 AM   #3
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Positive....2007 was on the only time Jeep made 4:10 standard in any package other than a rubi.....It was only for the auto JKU only didn't matter trim package....I was very pleased and surprise when I found that out.

Here are the items from the build sheet:
Vehicle Description JEEP WRANGLER UNLIMITED X 4X4 SPORT UTILITY 4-DOOR
Model Year 2007
Body Model JK J M 74
Color PBMA- Steel Blue Metallic Clear Coat
DJRS Next Gen. Dana 30 Solid Front Axle
DMFP 4.10 Rear Axle Ratio
DRZS Next Gen. Dana 44 HD Rear Axle
DS7S Conventional Differential Frt Axle
DS8S Conventional Differential Rear AxleTYXP P245/75R16 BSW On/Off Road Tires
TZAP Goodyear Brand Tires
WNJP 16X7.0 Aluminum Wheels
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Old 07-24-2013, 08:41 AM   #4
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Originally Posted by Raidan View Post
Positive....2007 was on the only time Jeep made 4:10 standard in any package other than a rubi.....It was only for the auto JKU only didn't matter trim package....I was very pleased and surprise when I found that out.
Interesting.

In that case you'll probably get better mileage with a bit bigger tire anywho because those 4.10s are too much for 245s. You need at least 255 or even 33s to match up well with them so don't fear making the jump to at least a 33" tire. The biggest factor for you is going to be how you use your jeep. From your description, it's a lot of miles each day and only very little off roading. No need for an aggressive MT tire. Since your on 16" wheels your options are 285/75/16 or 305/70/16 for a 33" tire. The latter being slightly bigger, wider, and heavier.
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Old 07-24-2013, 08:55 AM   #5
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I added the build sheet info to my post above.

ESP....have not thought about the gearing being too much for smaller tires....always here bigger tires too much for small gear ratio.....interesting point! Thanks for that.

Yeah I not wanting a MT but a good AT...really like the looks the Duratracs but also been looking at Cooper A/T3
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Old 07-24-2013, 09:00 AM   #6
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Originally Posted by ESP View Post
Things become interesting when moving to and above 33" tires. Depends wildly on your driving style and choose of tire.

If your driving 120 miles each day, you need a street tire or light AT. BFG AT or Duratrac no bigger than 33".
After the 1st week of driving it I was getting around 16.8 MPG...changed my driving habit by not going over 65 unless on the interstate and then only went the limit....really helped

with 33's how would things get interesting? Would I need a ProCal?? any advantage/disadvantage to 33x12.50R15 over 16's beside weight maybe?
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Old 07-24-2013, 09:03 AM   #7
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I ran 3.21s and a manual tranny with all of the tire sizes below.

225/75/16
245/75/16
255/75/17
33x12.5R15
305/70/16
315/75/16

Gears were fine until reaching 33x12.5R15s. I ran AT and MTs in this size and the ATs were fine. The MTs were a bit harder. Once I got to 35s they worked but left a lot to be desired.

I'm now using a 2013 with 3.73 and a manual tranny and the gears were way to much for the 225/75/16s that came on it. Constantly running higher than they should with that small of tire. Put on 33x12.5R15 KM2s and it's a much better fit. The RPMs have settled down and the pick and go is still there very much.

The goodyear duratrac is a great AT for what your describing.
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Old 07-24-2013, 09:05 AM   #8
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If you go from 245 to 285, 305, or 33x12.5, your speedo will be off and will need adjusting to be accurate. You can expect some mpg loss. 1-3mpg or so.
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Old 07-24-2013, 09:17 AM   #9
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I would highly suggest a Superchips Flashpaq for you. You can get then used for under $150 shipped. It will correct the speedo with different tire sizes, allows you to use the TPMS Off-Road feature to turn off the TPMS system along with some other great things.

To answer your original question. Per the dashboard fuel economy readout - I was averaging 18.1 mpg with my stock set-up. I added a 2" Teraflex Leveling kit and 33x12.50R15 Durtracs and now it is reading 16.5 mpg. Kind of surprising to me though as the 15" MB 72 wheels and Duratracs weigh in at 69 lbs each while my stock Sahara wheels and tires weighed in at 67 lbs. each.
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Old 07-24-2013, 09:22 AM   #10
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Just curious, how would OP (or a Rubi owner) do with 35 inch tires with the 4:10 gears?
Does this kill performance drastically or would it barely be noticeable with the new Pentastar power plant?
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Old 07-24-2013, 09:24 AM   #11
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^ exactly what I was gonna ask
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Old 07-24-2013, 09:40 AM   #12
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Quote:
Originally Posted by FXnut View Post
Just curious, how would OP (or a Rubi owner) do with 35 inch tires with the 4:10 gears?
Does this kill performance drastically or would it barely be noticeable with the new Pentastar power plant?
I don't think in my opinion he would notice much change. I am running a 3.21 gear with the new motor and just put 35s on and while its a bit more sluggish and does hunt for gears a bit more its not something that is terrible. The new motor has a better power band/torque curve so I don't think it's as dramatic as the older motor. My JK isn't a DD so I don't really care much that its a tad slower to 60. If I want to go fast I jump in my other car and mash it!!
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Old 07-24-2013, 10:28 AM   #13
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Quote:
Originally Posted by FXnut View Post
Just curious, how would OP (or a Rubi owner) do with 35 inch tires with the 4:10 gears?
Does this kill performance drastically or would it barely be noticeable with the new Pentastar power plant?
Quote:
Originally Posted by dukedallas View Post
^ exactly what I was gonna ask

With the 3.6, I'd almost recommend going 35's....or at least 33's with 4.10's if you do a lot of highway miles. Especially with an auto.

It is almost...too much gear. At 70mph, on stock Rubi wheels, you are turning 2500 rpms in 5th gear (on the auto).

The big benefit of the new tranny (and engine) that came out in 2012 was that Rubi's were basically "pre-geared' to be able to handle 35's if you got 4.10's. No re-gear necessary....that saved everyone $1500.
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Old 07-24-2013, 10:46 AM   #14
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The big benefit of the new tranny (and engine) that came out in 2012 was that Rubi's were basically "pre-geared' to be able to handle 35's if you got 4.10's. No re-gear necessary....that saved everyone $1500.
Nice! The reason I asked is my '08 JKUR was a slug with the 3.8 and stock tires, I'd hate to see it with 35s..

How does the new Rubi with 4:10s do with the 6 speed and 35s? Is there much difference in performance between the auto and stick?
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Old 07-24-2013, 10:55 AM   #15
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Nice! The reason I asked is my '08 JKUR was a slug with the 3.8 and stock tires, I'd hate to see it with 35s..

How does the new Rubi with 4:10s do with the 6 speed and 35s? Is there much difference in performance between the auto and stick?
They work great. There is obviously no torque converter, and in 2012, 6th gear was adjusted from .83 to .797...so 70 MPH with a +2012 manual turns about 100 rpms less than the auto on stock wheels....but you can still run 35's without a regear.

With 35's on a manual, 6th gear will turn about 2200 rpms with a stick.

The new engine helped both the auto and the stick...but the new tranny really changed the auto's.
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Old 07-24-2013, 12:31 PM   #16
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Thanks Panther! Great to know, I have manual xmission Rubi trying to work my way up to 35's already have 2in pucks in from the day i got it from the dealer. Just got the 18/59 springs, gonna go with Rancho 9000's with 3" larger size should leave me sitting pretty good for 35's . I'm gonna order the shocks sept and tires october.
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Old 07-31-2013, 07:57 AM   #17
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I have a 2013 Unlimited Rubicon, I would like to keep the stock 17" wheels, so whats the largest I can go tire wish and stay stock (no lift).
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Old 07-31-2013, 08:02 AM   #18
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I have a 2013 Unlimited Rubicon, I would like to keep the stock 17" wheels, so whats the largest I can go tire wish and stay stock (no lift).

Largest tire on stock JK? Here's your answer!
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Old 07-31-2013, 08:08 AM   #19
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I have an 07 with 33's and no lift and I average 12.9 and the best I have ever gotten on a long road trip was 15.4

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