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 Post subject: Gear Ratios
PostPosted: Sun Jul 03, 2011 3:49 pm 
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Location: Henderson
I don't think of myself as a rough jeeper, but I guess I must be. My 33" Goodrich All-Terrains were getting chunks out of the tread (and they weren't even that old, a year at most??). And, the tires seemed to be at the root of a recurring death wobble problem.

Since I needed more aggressive tires ANYWAY, I decided to get 35" Goodrich Mud-Terrains. Gear ratios didn't enter my mind. I have the standard gears that come on a stock Rubicon.

This jeep is my daily driver, but I only live three miles from work, so it doesn't get much of a daily workout. Of course, I do have to drive around town once in awhile, and on weekends, all bets are off. Hundreds of miles, up big hills, who knows? It's all possible on weekends.

I took the jeep out for its first taste of dirt with the new tires on Friday, and whereas before I could easily have zipped up the steep hill heading over toward Pahrump without even thinking about it, the jeep was NOT happy on that hill. Even flooring it, I couldn't keep the speed limit.

I don't MIND going slow up hills. I just want to know whether I'm at risk of damaging anything with 35" tires and the standard Rubicon gear ratio.

So, what do folks think?


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 Post subject: Re: Gear Ratios
PostPosted: Sun Jul 03, 2011 8:16 pm 
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I had 4.88's on my '05 rubicon LJ with 35's. That's with a manual trans. The stock gears were matched for 31's. 4.56's would have been good with the 33's. I thought these were the best setups but everyone sure has their own opinion. :D One mod always leads to another. Ask lots of questions first. We've all been there and done that several times over. Don't forget your speedo too.

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 Post subject: Re: Gear Ratios
PostPosted: Tue Jul 05, 2011 11:59 am 
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I beleave that Rubi's come stock with 4:10 gears, which by the way are the gears I run in D.D. for correction of 32" tires. Like Steve said 4:56's would have been fine for the 33" tires but to correct for 35" tires I would say 4:88's at least. Now I understand that when Rubicons first came out there were no 4:88 gear sets that would work with the factory rubi style dana 44 axles but that may have been corrected by now. Try the info on the Rubicon Owners Board or Bob should know.

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 Post subject: Re: Gear Ratios
PostPosted: Tue Jul 05, 2011 8:22 pm 
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Joined: Sat Aug 08, 2009 9:03 pm
Posts: 174
Location: Winnemucca, NV
Dawn Nelson wrote:
My 33" Goodrich All-Terrains were getting chunks out of the tread (and they weren't even that old, a year at most??).

It seems that you state that you don't off road the Jeep much, so I don't know if this is entirely applicable, but I'll toss in this.

Do you air down when in the dirt?

I run B.F.Goodrich All Terrain T/A KO tires (started running them in 1997 on my former truck, a '96 Chevrolet S-10 4WD pickup), but I'm sure that the Mud Terrain tires would be even more suseptible to this tendency than the All Terrains since they have larger blocks with wider separation between them for mud removal. In the past, I ran street pressure off road, my first set of All Terrains chunked badly. Chunking in that the tread blocks tear their outter edges and sometimes even entire blocks. When I mentioned something about it years ago and the suggestion to air down was made to me to eliminate that, chunking went away.

Lowering your tire pressure off road allows the tire to flex and mold themselves over sharp edged stones; running street pressures presents a stiff tread face to the stones, maximizing the chance for damage. Lowering tire pressures results in a softer ride off road as well, plus better floatation when encountering sand.

On road I run 35psi in my Toyota Tacoma. Off road I run around 15-18. Sometimes 20psi if I'm only running Class II two track trails with no known hazards.

If you don't want the inconvienience of airing back up when getting back to pavement, I've run 50+ miles with my tires aired down on pavement. My current 12v portable air compressor takes about 35-40 minutes to air back up all four tires, so if I'm not that far from home I simply drive home so I can air back up with my shop compressor. I've found that my All Terrains handle that just fine as long as I don't drive more than 55-60 home (although I've done 75 in winter) with no apparent over heating. However, I do slow down in corners as sidewall flex shows itself if you make sudden steering inputs (nothing scary, but it is a factor that I am aware of and make corrections for). However, southern Nevada summer temps are a consideration you might want to factor in before running home at lower pressures. However, my thinking is that a Jeep Wrangler is far lighter than my Tacoma, so that is a trade-off.


Dawn Nelson wrote:
I decided to get 35" Goodrich Mud-Terrains. Gear ratios didn't enter my mind. I have the standard gears that come on a stock Rubicon. ... the jeep was NOT happy on that hill.


I've got a friend with an automatic transmisson, 2-door JK Wrangler Rubicon with tires about that size (I forget the exact figure) and he went to a 4.88 ratio, the recommended for that size tire by the Dayton, NV off road shop that did his modifications.

Going oversize tire sizes is in effect lowering your overall gear ratio (lowering numerically - i.e. you know have something like 3.85:1 instead of 4.11:1 or whatever your Rubicon has). It also affects your ABS sensor input and operation, as well as your speedometer. And on road your gas mileage suffers as any uphill travel must be done while in lower gears (automatic or manual), higher RPMs or more open throttle settings or a combination of all. Being that modern Jeeps and all other vehicles are far more complex and computer controlled, it may affect other things as well.

As stated before, each modification often presents side effects, which take time and $$$ to overcome. If you go bigger in tires, it is better for your Jeep on and off road to re-gear your differentials.

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Last edited by David A. Wright on Wed Jul 06, 2011 8:14 pm, edited 1 time in total.

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 Post subject: Re: Gear Ratios
PostPosted: Wed Jul 06, 2011 6:06 pm 
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Joined: Tue Jul 04, 2006 3:10 pm
Posts: 320
Location: Henderson...
Dawn,
4.10 is perfect for 33" tires ....you went to 35" and the gears are now not "tall enough"
you experienced that already and also your Speedometer is off by at least 11%
you will end up getting a speeding ticket if your not careful.
use a GPS and will will see your exact speed vs the Spedo

don`t mess with the 4.56 you will regret it.
4.88 ratio <---- minimum ...yes they make the "thick gears" you will need.

http://www.northridge4x4.com <--- best price tell David you know "mac"

Ted Weins 4x4 or Adams can do the install for you.
it`s always good to shop around.
make sure you get a proper break in done once you get new gears...follow the directions!

you will also need a speedometer correction device installed...
the dealer WILL Not fix it for you... ask David @ Northridge what is the best type to correct.
:mrgreen:

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 Post subject: Re: Gear Ratios
PostPosted: Wed Jul 06, 2011 6:13 pm 
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Joined: Mon Jan 23, 2006 9:15 am
Posts: 314
Location: Henderson
Hey Folks,

Thanks for all the information. I love learning this stuff. (Spoken like a true teacher).

I know gas mileage and performance will suffer, and certainly, I have no problem with getting different gears. It's just the money thing. The big question, at least for the moment, until I decide to spend the money, is... am I ok to keep the 4:10 gears for now, or do I risk damaging something which will make a more costly repair later?

I had to chuckle when asked, "Do I air down?" Now only do I air down, I have mt own CO2 tank for airing back up! I tried airing down once, and now I can never go back. Ask Beth. We both discovered the delights of squishy tires on the same run. :D


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 Post subject: Re: Gear Ratios
PostPosted: Fri Jul 08, 2011 9:08 am 
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Location: Las Vegas
Dawn, in your search engine, type "tire to gear ratio" (or something to that effect) and you will find a chart that's easy to follow. You'll find that 35 inch tires and 4.56 gears are a near perfect factory fit. 4.88 will give you more power and less gas milage. I love my 4.56 with 35's. I guess it's a personal thing.

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 Post subject: Re: Gear Ratios
PostPosted: Fri Jul 08, 2011 5:20 pm 
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And after thinking about it for a little while, which gave me a headache by the way, your tire chunking problem could have been caused by excessive air pressure when on the street. What psi do you run them at when driving in town? A wrangler on 35's may only need to aired up to 26 to 30 psi. There is a great and easy test for needed on road pressure I can share with you if you want.

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Re-located from my beloved Mojave to Texas. Where did all the mountains go???


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 Post subject: Re: Gear Ratios
PostPosted: Sat Jul 09, 2011 9:12 pm 
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Joined: Mon Jan 23, 2006 9:15 am
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Location: Henderson
Now, stop that thinking. Especially if it gives you a headache. Interesting idea about the chunking. I think it was from jeeping, though, because I first noticed it soon after a jeep run. I've got the 35s at 38 psi right now.

If the air test involves chalk, I know about it, but haven't tried it. In fact, you're the one who told me about it, and you even gave me a piece of sidewalk chalk! It has been sitting in my garage for years now, waiting for me to get my act together and use it. :roll:

As for the gears, I heard from the guru of John Crooks, who said that I shouldn't have to worry about my current set up actually damaging anything. And for now, that's what I needed to know.


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 Post subject: Re: Gear Ratios
PostPosted: Sun Jun 09, 2013 5:37 pm 
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Joined: Sat Jun 01, 2013 4:33 pm
Posts: 9
Location: Las Vegas
You will not hurt a thing. Just be aware of what speed and rpm the jeep can do comfortably going up hill. No need to push it hard to save a minute or two of drive time. Will be a little slower but that will just give passers by more time to oogle over the BIG jeep. A happy jeep leads to a happy jeeper


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