Optimal 4x4 Gearing Q's

[Zenobian_84]

As of this moment, I'm running a 2.5 / AX-4 / D35 (with 3.55s) and will hopefully one day get my grubby hands on a donor XJ/MJ with a 2.5 and 4x4 to add said 4x4 to my own truck (plus, adding a D44 rear).

 

My questions are:

 

1. If this is purely a DD rig (factory specs, no lift, no rock crawling, no running tires over the 235/75/15 size, and only the occasional light duty off-roading) when I add a 242/231 TC etc., what gear ratio is the most optimal to run? The 3.55s as they are right now do a pretty decent job of getting me where I need to go, but I don't know if the gains of going to either a 4.10 or higher is what I should look into more.

 

2. IIRC, there was a thread around here somewhere explaining the different Jeep gear ratios, and the pros and cons of each one. Don't know if it was just a reply to someone's thread though. :hmm: Obviously, real rock crawlers and 4x4 enthusiasts shoot for lower gearing on their off-road only rigs, but why? Is it purely just the want for that lower revolution ratio, or is there more to it than that? Can the same be said for Jeeps w/ 3.07s or 3.55s verses 4.10s and higher?

[DREDnot]

My 2.5L has the 4.56 gear. Seems like the bare minimum needed given the meager horsepressure of the 4 cylinder.

[jimoshel]

My DD, A 2.5 with 4sd has 3.53 gearing. It's just right for a DD. However any kind of a load or a trailer and the lack of horse power is evident. Although it gets the job done.

[Regger]

In stock form, my 88 4x4 had the 4.0L, 5spd, D30/35 and had 3.08 gears. The gears were horrible!! I could barely use 5th gear on hills.. It was made even worse when I stepped up to 33's. By the calculations, to remain with the stock gearing, I should have stepped up to 3.73's. Instead I went with 4.10's. A 25% increase in gearing.. It was awesome!! I could use 5th gear going up hills, could tow a lot easier, and it was just a lot easier to drive and not having to ride the clutch in some instances to get going. And I even got better mileage because the engine didnt have to work as hard to maintain speed even with the 33's.

Now, not having driving a 4cyl in stock form, I can't say how the gearing feels. But from talking with other friends with similar setups, they all seem to agree that even a step up in gearing would be better... ( ie, 3.08 to 3.55, 3.55 to 3.73, 3.73 to 4.10...)

Now that my 88 is a dedicated rock-crawler... I stepped up as high as one could go with D44 gearing, all the way to 5.89's with 36's. Yes that gearing is super low, almost too low if you want to ever drive it on the highway. Driving around town city driving, I'm in 4th gear all the time. 5th gear barely gets me to highway speed, and at that I'm not far off from redline.

The reason rock-crawlers want super low gearing is for the throttle control and torque. Because we're not racing around a course, we need that horsepower to crawl over rocks and obstacles. Having super low gearing allows to let off the clutch instantly and crawl your way up a rock, and not having to ride the clutch to go slow.

I would recommend that you step up to at least 3.73, if not 4.10(i think 4.10 is stock in a 4cyl, 4x4). Cause now you will be pushing a heavier front axle around as well. And just look at what you want to do with your truck, if its to remain stock, then at the minimum go with what the stock gearing was for that setup or at least step up one ratio for better performance. If it will be used for towing and off-roading, I recommend at least a 25% increase over stock gearing.

 

HTH

Ryan

[Eagle]

1. If this is purely a DD rig (factory specs, no lift, no rock crawling, no running tires over the 235/75/15 size, and only the occasional light duty off-roading) when I add a 242/231 TC etc., what gear ratio is the most optimal to run? The 3.55s as they are right now do a pretty decent job of getting me where I need to go, but I don't know if the gains of going to either a 4.10 or higher is what I should go for.

A couple of points:

 

(a) A 2.5L 4-cyl probably came from the factory with 195/75 or at most 205/75 tires, so running 235s is already way oversized for that vehicle. In fact, a 235/75 is virtually the same as a 30x9.50, just a tad narrower.

 

(B) Adding a transfer case doesn't affect your gearing. The 2WD position is a 1:1 ratio. If you're happy with the gearing now, stay with it. But more than likely if you find a 2.5L XJ or MJ with 4WD it will be mated to a 5-speed. In that event, going to 4.10s will allow you to take advantage of the improved crawl ratio for off-road while maintaining driveability on pavement.

[Zenobian_84]

In stock form, my 88 4x4 had the 4.0L, 5spd, D30/35 and had 3.08 gears. The gears were horrible!! I could barely use 5th gear on hills.. It was made even worse when I stepped up to 33's. By the calculations, to remain with the stock gearing, I should have stepped up to 3.73's. Instead I went with 4.10's. A 25% increase in gearing.. It was awesome!! I could use 5th gear going up hills, could tow a lot easier, and it was just a lot easier to drive and not having to ride the clutch in some instances to get going. And I even got better mileage because the engine didnt have to work as hard to maintain speed even with the 33's.

Now, not having driving a 4cyl in stock form, I can't say how the gearing feels. But from talking with other friends with similar setups, they all seem to agree that even a step up in gearing would be better... ( ie, 3.08 to 3.55, 3.55 to 3.73, 3.73 to 4.10...)

Now that my 88 is a dedicated rock-crawler... I stepped up as high as one could go with D44 gearing, all the way to 5.89's with 36's. Yes that gearing is super low, almost too low if you want to ever drive it on the highway. Driving around town city driving, I'm in 4th gear all the time. 5th gear barely gets me to highway speed, and at that I'm not far off from redline.

The reason rock-crawlers want super low gearing is for the throttle control and torque. Because we're not racing around a course, we need that horsepower to crawl over rocks and obstacles. Having super low gearing allows to let off the clutch instantly and crawl your way up a rock, and not having to ride the clutch to go slow.

I would recommend that you step up to at least 3.73, if not 4.10(i think 4.10 is stock in a 4cyl, 4x4). Cause now you will be pushing a heavier front axle around as well. And just look at what you want to do with your truck, if its to remain stock, then at the minimum go with what the stock gearing was for that setup or at least step up one ratio for better performance. If it will be used for towing and off-roading, I recommend at least a 25% increase over stock gearing.

 

HTH

Ryan

Interesting points Ryan, thanks :cheers:

 

A couple of points:

 

(a) A 2.5L 4-cyl probably came from the factory with 195/75 or at most 205/75 tires, so running 235s is already way oversized for that vehicle. In fact, a 235/75 is virtually the same as a 30x9.50, just a tad narrower.

 

(B) Adding a transfer case doesn't affect your gearing. The 2WD position is a 1:1 ratio. If you're happy with the gearing now, stay with it. But more than likely if you find a 2.5L XJ or MJ with 4WD it will be mated to a 5-speed. In that event, going to 4.10s will allow you to take advantage of the improved crawl ratio for off-road while maintaining driveability on pavement.

 

Also noted. I find it wierd though that my factory tire pressure chart inside the glovebox has ratings for my specific tire. Going from 195 all the way to 235s. I figured the stock tires were probably 205s, but didn't think that going to 235s would put serious strain on the drivetrain. I do believe that 4:10s are what I'm going to be shooting for. Even at the very least, if I only upgrade my D35 to a 44, I'll be pretty darn happy. :yes: