Choosing gear ratio, JKU

[GFA]

Ok, so I have a 2010 JKU auto with 3.73's. I'm sitting at discount tire getting 285's installed and thinking how much worse its going to be when it wouldn't pull a wet noodle from a greased cats *** on stock tires. I don't mind loosing some MPG's to be able to pull mountain passes with my M416 in tow without redlining it but also don't want to over gear it.

A typical load when traveling will be 5 people and all associated gear for a long weekend or longer in the M416. I'd guess it weighs in at 1800lbs or so loaded. I put off a trip out west this summer after towing a pair of jet skis to a lake in the VA foothills, it just would not have been capable in the Rocky's with even more weight in tow.

I'm thinking 4.88's but gear charts I see for JK's put 488's at the lower end of acceptable for these tires and that doesn't take into acct for towing. Would 5.13's be better or is that getting to steep?

As a side note, I bought new black rock wheels for it and realized that they are a dual lug pattern wheel when they arrived. 5 on 5 and 5 on 5.5. I went ahead and ordered 2 more for the M416 so I can have a common spare. I've seen where many people get custom trailer axles to have the same lug pattern as the jeep but had never seen dual patterned wheels mentioned as an option. Just thought I'd throw it out there for anyone interested...

SB

 

[JRCCRW]

I had 4.56's in my 2010 JKU auto and it pulled just fine. I was running 285 75R16 BFG's and I pulled an M100 all over the place. I didn't loose much gas mileage and I also didn't tackle big rocks either. If I had to do it again, based solely on my experience with mine, I would not have wanted 5.13's. I, at one time, thought that I might want to go up to 315's, but the 4.56's would not have been enough. Make sure you are completely sure on your final tire size before you choose your ratio.

Hope this helps.

 

[JIMBO]

:sombrero: Generally accepted in 07 thru11 JK/JKU/w auto-
--4.56--rare

--4.88 for DD and light towing/off-roading

--5.13 for non-DD and heavy towing/off-road use

--5.38 for Rubis (Dana 44s) and NO DD, strictly off-road use, unless your commute is non-freeway-

For a 6-spd--any ofem, depends on your use and tire size

Lotta choices-

:costumed-smiley-007:wings: JIMBO

 

[wADVr]

I would say 5.13s would be a good option for you. if you were to go to 35s 5.38s would be perfect. A little extra RPM is a good thing with the little underpowered 3.8, I have 5.38s with my 37s and strongly feel it is still under geared.

 

[GFA]

Thanks for the insight. I'm leaning towards the 4.88's as of now but I've got a month or so to decide.

I also do a lot of highway driving at 70+ mph so I should really consider that factor more so than the occasional towing I do. That being the case, I definitely think 4.88's would be better to keep the fuel mileage reasonable. It's only a 120 RPM difference though from 4.88 to 5.13 at 70mph though so is that really a big difference?

SB

 

[redthies]

First off, which 285? 70 or 75? I just today put Toyo AT IIs in 285/75-17 on the Rubicon. It's a 2011 with auto. To hear everyone else tell it, I won't be able to pull the skin off a pudding now. Hmmm. 0-60 in 16.0 with stock 255s. 16.1 with the new tires. Wow, this thing is a rocketship! Thank goodness I listened to all the wisdom on the intraweb.

Long and the short of it, unless you live in Colorado, 4.88s are more than enough with either 285.

 

[NFRs2000NYC]

Careful with going too far. With 5.13s your pinion is getting small and the strength is compromised.

 

[GFA]

Careful with going too far. With 5.13s your pinion is getting small and the strength is compromised.

If this engine developed any torque I'd be concerned about that, but... LOL. For the type of driving I mainly will be doing I don't think it would be an issue.

I've had a chance to put some miles on the 285's (70's) now and can't really tell a difference honestly. I've yet to hit the highway though. I never expected it to be a race car but its pretty embarrassing to be passed on a slight hill by a Chevy volt...

I'll be doing some more reading before the swap but as of now I'm thinking the 4.88's are my best option.

 

[JIMBO]

:sombrero: I gotta agree with ya, 4.88s have pleased a lotta jeep JKU owners, mainly because they are able to use the jeep as a DD and still have larger/fatter tires for doing light/medium off-roading-

If this engine developed any torque I'd be concerned about that, but... LOL. For the type of driving I mainly will be doing I don't think it would be an issue.

I've had a chance to put some miles on the 285's (70's) now and can't really tell a difference honestly. I've yet to hit the highway though. I never expected it to be a race car but its pretty embarrassing to be passed on a slight hill by a Chevy volt...

I'll be doing some more reading before the swap but as of now I'm thinking the 4.88's are my best option.

When you get over the sudden magical power/performance increase, you'll start to notice an increase in MPG--

I mentioned 5.38s and the change to the overweight JKU is breathtaking--I'm afraid the suggestion of reduced pinion size for the D30 is true, the 3.8L v6 produces more than enough torge to cause ring/pinion damage when tire size is increased and 5.13/5.38 gears are used !

Good luck

:costumed-smiley-007:wings: JIMBO

 

[NFRs2000NYC]

Apologize for the previous post, I forgot about the 2010 part, so 4.88s are fine, but I still maintain that 5.XX on a D30 would make the pinion pretty small, so unless you are not looking to do anything more challenging than a dirt road, I personally wouldn't feel comfortable taking it out to the Maze district for instance. While it may be fine, it's not something I'd want hanging over my head. To each their own of course.

 

[Judoka]

4.56... Really people? :Mechanic:

 

[NFRs2000NYC]

4.56... Really people? :Mechanic:

4.56s are power gears for 2012s, hence why you see recommendations for them. Some (myself included) forgot that it's a 2010 in question.