I want bigger tires... but

[jimsmith29841]

Then he's too stupid to know what he's missing out on, plain and simple.

You're not going to have any "problems" with 3.73 gears, it's just going to be far from ideal with that gearing and 35s. Guarantee if this guy put the proper gears in he would be kicking himself for not doing it sooner.

So what you have here is simply a case of someone who merely doesn't know any better.

The 42RLE came in all 03-06 TJs with automatic transmissions.

Agreed.
2004 JeepTJ 4.0 Sport
I am running 32" Hankooks A/T, 4speed Auto with 3.73.
Its runs ok on the highway and ok offroad, but I feel like I am at that threshold where I do NOT need to go with any larger tire size unless I gear it also.

 

[ErikOffroad]

@ErikOffroad You’re wasting your money. You’ll never be that guy on the side of the trail sitting there with your wife cursing you for two hours. Upgraded chronology shafts would be a good move

Thanks. I’ll probably be doing axle builds in the fall so I will start a thread later to see what parts I should be looking to buy. I’m about to drop a bunch of money on Currie control arms and get that in this spring first, as well as doing some pm work. I’m looking forward to being locked and loaded but for now I’m just taking it easy and not doing any serious climbing with the Jeep. Mainly just trying to get a feel for the vehicle. It’s still pretty impressive as to what it can do now the way it sits.

 

[JMT]

Thanks. I’ll probably be doing axle builds in the fall so I will start a thread later to see what parts I should be looking to buy. I’m about to drop a bunch of money on Currie control arms and get that in this spring first, as well as doing some pm work. I’m looking forward to being locked and loaded but for now I’m just taking it easy and not doing any serious climbing with the Jeep. Mainly just trying to get a feel for the vehicle. It’s still pretty impressive as to what it can do now the way it sits.

I ran a Dana 30/35 combo with 33’s and did some level 4/5 stuff at Hidden Falls. I was ok going easy on the skinny pedal.

Now I run a Dana 30/44 combo with the same 33’s and front has a lunchbox locker and rear is a spool for a few more days. Eaton e-locker going in the rear and 456 gears.

If I go to 35’s I will upgrade the shafts front and rear. The front just doesn’t see the forces the rear does.

Best to you

 

[ErikOffroad]

I ran a Dana 30/35 combo with 33’s and did some level 4/5 stuff at Hidden Falls. I was ok going easy on the skinny pedal.

Now I run a Dana 30/44 combo with the same 33’s and front has a lunchbox locker and rear is a spool for a few more days. Eaton e-locker going in the rear and 456 gears.

If I go to 35’s I will upgrade the shafts front and rear. The front just doesn’t see the forces the rear does.

Best to you

Are you swapping the carrier your self or having a shop do it. I haven’t messed with differentials in 10 years. I was going to see if you where going to do one I can possibly get a refresher course on it. A lot of the equipment I deal with is hydraulic driven so I never had to deal with a broken diff.

 

[JMT]

Are you swapping the carrier your self or having a shop do it. I haven’t messed with differentials in 10 years. I was going to see if you where going to do one I can possibly get a refresher course on it. A lot of the equipment I deal with is hydraulic driven so I never had to deal with a broken diff.

I did the front locker myself. It reused the stock carrier.

I’m having a shop do the gears and rear locker. I read Billavista’s gear bible multiple times and understand the process, but don’t have the tools to do it. At the fear of screwing things up I opted to pay a shop $950 total rather than buy the tools. She goes in next week.

Gears can be done but it takes a ton of patience and knowledge. Very few can do it sufficiently. It’s the one job I think is best left to the pro’s. I’ve done everything else on my rig myself

 

[ErikOffroad]

That’s my problem is I don’t ever stop till I figure it out. I once bought a broken jet ski for 500 dollars and fixed it in one day for 20 bucks, now I think I’m marine mechanic. And I’m only a dial indicator and a inch pound torque wrench away from having all the tools

 

[mrblaine]

If I go to 35’s I will upgrade the shafts front and rear. The front just doesn’t see the forces the rear does.

Best to you

In general that is true until it isn't. It isn't once you put in lockers and can get into situations where you need to back up something to reposition, or you hang the rear diff and get the fronts where they have high traction. That is when the breakage happens, when you actually do subject the front to the forces the rear sees.

 

[jimsmith29841]

Thanks. I’ll probably be doing axle builds in the fall so I will start a thread later to see what parts I should be looking to buy. I’m about to drop a bunch of money on Currie control arms and get that in this spring first, as well as doing some pm work. I’m looking forward to being locked and loaded but for now I’m just taking it easy and not doing any serious climbing with the Jeep. Mainly just trying to get a feel for the vehicle. It’s still pretty impressive as to what it can do now the way it sits.

I agree that it is quite capable as it is, mine came with trak-loc in the rear and it has been more than enough for what I do with her the only changes coming in the future are new ujoints all around and an e-locker on the front.
I still want it to be a decent ride on the interstate highways carrying snowboards in the winter, rockclimbing gear in the summer and a surfboard to the beach.
Haven't figured out how to strap a surfboard to the top yet.

 

[JMT]

That’s my problem is I don’t ever stop till I figure it out. I once bought a broken jet ski for 500 dollars and fixed it in one day for 20 bucks, now I think I’m marine mechanic. And I’m only a dial indicator and a inch pound torque wrench away from having all the tools

View attachment 74993

You even have the right shoes just sitting there ready to put on! Nice garage...

 

[mgroeger]

There was a transition in the Jeep tj automatics when they switched to the 42rle (what’s in mine) in 2003. Now which transmission your friend has could change his experience. Attached is some info regarding the difference and years. You can see in the pictures the final ratios (OD) which is what most people regear for when they do highway driving on bigger tires.View attachment 74770View attachment 74771
A 1:1 overdrive isn’t bad at all with his setup (i’d still prefer lower gears for torque at highway speed) but as you can see the 42rle (newer tj trans) is a dog with 0.69 OD. When you add in the considerable mass of 35” tires and any other weight you’re carrying anything higher than 5.38 gears will lug the engine unless you’re doing 75+ mph. You can get away with 5.13 but the jump is just nicer.

So I have a noob gearing question:
Why do they say you need to go with "lower" gears but the ratio is actually going higher... 4.10, 4.88, 5.38, etc... and vice versa for "higher" gears?

 

[Mr. Bills]

It probably traces back to the good old days when 3rd or 4th gear in manual transmissions was called "high gear" "top gear" as was "D" in auto transmissions.

"Lower" gears are numerically greater than "high" gears. Here are two examples of low and high transmissions gears:

42RLE 4-speed auto trans: 1st gear [Low] is 2.84:1, 2nd is 1.457:1, 3rd is 1.0:1 [High] and 4th (overdrive) is 0.69:1.

AX15 5-speed manual transmission: 1st gear is 3.83:1, 2nd is 2.33:1, 3rd is 1.44:1, 4th gear is 1.0:1 [High] and 5th (overdrive) is 0.79:1.

 

[BuildBreakRepeat]

So I have a noob gearing question:
Why do they say you need to go with "lower" gears but the ratio is actually going higher... 4.10, 4.88, 5.38, etc... and vice versa for "higher" gears?

The reason they are referred to as higher vs lower gears has to do with the relationship between the engine speed to final gear. The lower the gearing, the lower your tire speed is in comparision to engine rpm. A 1:1 (1.0) final drive ratio means that when the input (or engine) turns 1 reveloution the tires (or output) then turns one reveloution. Now let’s say you were to use something “lower” or a 1:4.10, 1:4.88, or 1.5.38. While the engine still turns that 1 reveloution. The tires don’t turn a full one...the tire speed in relation to the engine speed gets lower and lower the larger the number you put! If I have a 1:100 ratio (extremely low) I’m gonna see one turn of the engine only turning the tire 1/100th of a reveloution. Does that make sense? I kinda went far in detail. High gear is the reverse of this...even to the point of “Over drive” where the gearbox or final drive output is higher than the RPMs of the engine or “over” geared. The simplest way to look at it is tire rotation speed. Lower gears = lower tire reveloutions for a set engine speed. Higher gears = higher tire reveloutions for a set engine speed.

 

[steelhd]

My apologies as I know somewhere on here I asked this question on a thread but I can't find where it is, hence this thread.

2004 LJ automatic.
I have Dana 44s front and rear with 4.88 gears and I am running 33s x12.5 on 15" rims
I was told DON'T go to 35s unless I go to 5.38 gears because of the OD in this transmission and how it LOVES to stay in OD. I have experienced this even with the 33s where I will kick the OD off when getting on highway ramps or up long hills annoying but still only a first world problem.

I met a guy with a 2003 TJ who is running Dana 44 in the rear and I forget what up front (I think 44 as well). He has and automatic and 3.73 gears and is running 35s with no problem at all, he said it doesn't struggle on or off road. What's the deal? Is the tranny different between '03 and '04?

I have an 04 LJ with the stock auto and transfer case, D44s, 4.88s, 35s, and everything is just fine. Drives fine in town, drives fine on the freeway, and it wheels just fine. All it really needs is a Rubicrawler. Thsts next on my list along with a cage. The trick when driving anywhere other than the freeway is to just use the OD off button. Easily ingrained habit. I didn't even think about reaching for the button after owning the Jeep for a few weeks.

 

[jjvw]

I have an 04 LJ with the stock auto and transfer case, D44s, 4.88s, 35s, and everything is just fine. Drives fine in town, drives fine on the freeway, and it wheels just fine. All it really needs is a Rubicrawler. Thsts next on my list along with a cage. The trick when driving anywhere other than the freeway is to just use the OD off button. Easily ingrained habit. I didn't even think about reaching for the button after owning the Jeep for a few weeks.

What about those who want to use the OD?

 

[Mr. Bills]

I tried the "I can use the OD button" rationalization on my LJ with 42RLE, 4.88 gears and 35" tires. The problem was the voice in my head every time I used the OD button that said, "You wouldn't need to do this if you had the right gears."

I re-geared to 5.38 and the world is perfect once again.

I will say this to those with 4.88 gears, 42RLE transmission and 35" tires: If you think your jeep is driving just fine you are proving the adage, "you don't know what you don't know." Try to drive a similarly equipped jeep with 5.13 or 5.38 gears. It will be an enlightening experience.

 

[BuildBreakRepeat]

I tried the "I can use the OD button" rationalization on my LJ with 42RLE, 4.88 gears and 35" tires. The problem was the voice in my head every time I used the OD button that said, "You wouldn't need to do this if you had the right gears."

I re-geared to 5.38 and the world is perfect once again.

I will say this to those with 4.88 gears, 42RLE transmission and 35" tires: If you think your jeep is driving just fine you are proving the adage, "you don't know what you don't know." Try to drive a similarly equipped jeep with 5.13 or 5.38 gears. It will be an enlightening experience.

Couldn’t have said it better myself!

 

[steelhd]

What about those who want to use the OD?

In town at 25 to 35 mph? Nobody wants to, or really should, be lugging their motor. I said freeway but I misspokeva bit. At about 45 I let OD come back on.

 

[glwood]

In town at 25 to 35 mph? Nobody wants to, or really should, be lugging their motor. I said freeway but I misspokeva bit. At about 45 I let OD come back on.

The problem with that on mine is the torque converter locks up sooner in 3rd gear on my 42RLE, which lowers the rpms too much, too soon, when I have the O/D off button pushed. Very annoying.

 

[steelhd]

I will say this to those with 4.88 gears, 42RLE transmission and 35" tires: If you think your jeep is driving just fine you are proving the adage, "you don't know what you don't know." Try to drive a similarly equipped jeep with 5.13 or 5.38 gears. It will be an enlightening experience.

I know exactly what I'm missing. The OP wrote;

"I have Dana 44s front and rear with 4.88 gears and I am running 33s x12.5 on 15" rims
I was told DON'T go to 35s unless I go to 5.38 gears because of the OD in this transmission and how it LOVES to stay in OD."

Emphasis was on the word DON'T which is kind of stupid. A higher ratio would certainly be preferable when time and money allow. But there is really no reason to not go with 35s if he wants to since it can be held out of OD at low speeds. Personally my financial path is cage then Rubicrawler then gears then 37s.

 

[LukesfirstJeep]

I will say this to those with 4.88 gears, 42RLE transmission and 35" tires: If you think your jeep is driving just fine you are proving the adage, "you don't know what you don't know." Try to drive a similarly equipped jeep with 5.13 or 5.38 gears. It will be an enlightening experience.

Mr Bills, thank you. You and Jerry B. have given me the information to confirm the gearing for my particular setup. I won't be running 35" tires, but I put your setup in GrimmJeeper's calculator. I put the gear ratio I chose for my set up into the calculator and it matches (within 50 RPM) the RPM's of your setup for the various speeds.

I only know what how my jeep runs with a less than optimal gear ratio and look forward to regearing and experiencing what others are talking about.