Regearing from 4.88 to Revolution Gear's new 5.38... sweet!

5.13 is a bit deep if you are running 80 on the hwy. 4.88 would lower rpm's by about 200, so not a huge difference. Either slow down or go 4.56, you speed demon :D

Funny, I went with 4.56 gears on a 2000 TJ 5-speed with 35's and it's perfect for me because I usually cruise at 70-75 mph on the highway. I got some grief on another forum because some self-appointed 'expert' insisted that I should've gone with 4.88 gears, but I knew that I didn't want a buzzy engine running over 2,500 rpm for long distances. I'm technically not operating at the peak of the torque curve and occasionally have to downshift to 4th on really steep hills but I was targeting highway comfort and drivability more than anything else. Once I'm off-road, especially in 4-low, I don't feel like the axle gearing matters so much and I'll eventually upgrade the transfer case from 2,7 to 4-1, which will make a much greater difference.

The gear ratios on the automatic transmission are different than the manual - top gear .69 vs .79 on my 5-speed - so I'm not surprised Jerry really likes the new 5.38 gears. While I was building up my Jeep, I briefly drove it with 35's and the stock 3.73 gears and that's just miserable.
 
  • Like
Reactions: Rob5589
I’m confused, I was told the Dana 44 carrier (Rubicon with lockers) can’t handle the 5.38 size and 5.13 was the max?. I have 33s right now, at 62lbs each. HEAVY for 33s. I found 25s at around the same width and same weight 61 lbs. Can I assume these tires would function the same on the same gear ratio? Or is that stupid? I want to eventually get 35s but I have stock gearing right now and want to upgrade once and be done with it, but I don’t think I can upgrade to 5.38 with 33s (even if they are heavier than 35s). I am thinking about going to 5.13s with my heavy 33s and then when I get 35s eventually just deal with them on the 5.13 ratio. I have the Rubicon 42RLE tranny
 
I have 33s right now, at 62lbs each. HEAVY for 33s. I found 35s at around the same width and same weight 61 lbs. Can I assume these tires would function the same on the same gear ratio? Or is that stupid? I want to eventually get 35s but I have stock gearing right now and want to upgrade once and be done with it, but I don’t think I can upgrade to 5.38 with 33s (even if they are heavier than 35s). I am thinking about going to 5.13s with my heavy 33s and then when I get 35s eventually just deal with them on the 5.13 ratio. I have the Rubicon 42RLE tranny

I wouldn't call it "stupid" because that's not nice but you're missing an important fact that the overall gear ratio doesn't stay the same just because you found 35's with the same width and weight as your 33's. There is another input into the calculation and the diameter of the 35's is increased compared to 33's, therefore the overall gear ratio becomes taller and you will lose engine rpm at the same speeds. In fact, most people re-gear their vehicles to compensate for the diameter of their new bigger tires, not so much the potential weight and width increases.
 
I wouldn't call it "stupid" because that's not nice but you're missing an important fact that the overall gear ratio doesn't stay the same just because you found 35's with the same width and weight as your 33's. There is another input into the calculation and the diameter of the 35's is increased compared to 33's, therefore the overall gear ratio becomes taller and you will lose engine rpm at the same speeds. In fact, most people re-gear their vehicles to compensate for the diameter of their new bigger tires, not so much the potential weight and width increases.

Ok this is just what I was looking for, thanks for the info! Appreciate it
 
Ok this is just what I was looking for, thanks for the info! Appreciate it

You're welcome. Go back to the first post in this thread and Jerry actually points out that he is spinning 2,600 rpm at 70 mph with 5.38 gears, which obviously fit in his Dana 44 axle. Since I tend to drive at slightly higher speeds, I personally might go with 5.13 gears if I had Jerry's Jeep because 2,600 rpm is already past my upper limit that I would want to tolerate for extended periods and it would be even higher at 75 mph.

Something you may want to try out with your current setup is to just get on the highway and drive your Jeep a couple of miles at 2,400 rpm, then another couple of miles at 2,500 rpm, then 2,600 rpm and so on. That should give you a pretty good idea as far as what you prefer for your cruise speed rpm (ignore the actual speed in mph, that would change when you go to 35's). If, for example, I changed the gearing in my Jeep from 4.56 to 5.13, I would experience a fairly dramatic increase in rpm at highway speeds, and then would have to decide if I'm willing to drive 3 hours to the mountains with the engine at about 3,000 rpm the whole way. Obviously I don't, which is why I selected 4.56 gears. There are always trade-offs with gearing but spend some time deciding because it's not all that cheap to change gearing a second time if it doesn't work out like you had hoped.

Ideally, hook up with another Jeep owner who has the gear ratio you're considering and see if they'll take you for a spin.
 
  • Like
Reactions: dylansalrin
I’m confused, I was told the Dana 44 carrier (Rubicon with lockers) can’t handle the 5.38 size and 5.13 was the max?. I have 33s right now, at 62lbs each. HEAVY for 33s. I found 25s at around the same width and same weight 61 lbs. Can I assume these tires would function the same on the same gear ratio? Or is that stupid? I want to eventually get 35s but I have stock gearing right now and want to upgrade once and be done with it, but I don’t think I can upgrade to 5.38 with 33s (even if they are heavier than 35s). I am thinking about going to 5.13s with my heavy 33s and then when I get 35s eventually just deal with them on the 5.13 ratio. I have the Rubicon 42RLE tranny
Jerry mentioned that the 5.38 is fairly new and with the pinion being the same size as the 5.13 making the 38 doable on that carrier.
 
  • Like
Reactions: dylansalrin
Funny, I went with 4.56 gears on a 2000 TJ 5-speed with 35's and it's perfect for me because I usually cruise at 70-75 mph on the highway. I got some grief on another forum because some self-appointed 'expert' insisted that I should've gone with 4.88 gears, but I knew that I didn't want a buzzy engine running over 2,500 rpm for long distances. I'm technically not operating at the peak of the torque curve and occasionally have to downshift to 4th on really steep hills but I was targeting highway comfort and drivability more than anything else. Once I'm off-road, especially in 4-low, I don't feel like the axle gearing matters so much and I'll eventually upgrade the transfer case from 2,7 to 4-1, which will make a much greater difference.

The gear ratios on the automatic transmission are different than the manual - top gear .69 vs .79 on my 5-speed - so I'm not surprised Jerry really likes the new 5.38 gears. While I was building up my Jeep, I briefly drove it with 35's and the stock 3.73 gears and that's just miserable.
Yep, big difference in the final drive between the auto/od and manual.
 
With the 42rle, 33’s and 5.13 gearing:

f3RSjsR.jpg
 
I’m confused, I was told the Dana 44 carrier (Rubicon with lockers) can’t handle the 5.38 size and 5.13 was the max?.

I'm pretty that even the 5.13's were not available in thick cut versions until Revolution had them developed at the same time as the 5.38's about 3 years ago. Until then, you had to change the carrier to work with the available thin or regular pattern gear sets.

I have 33s right now, at 62lbs each. HEAVY for 33s. I found 25s at around the same width and same weight 61 lbs. Can I assume these tires would function the same on the same gear ratio? Or is that stupid? I want to eventually get 35s but I have stock gearing right now and want to upgrade once and be done with it, but I don’t think I can upgrade to 5.38 with 33s (even if they are heavier than 35s). I am thinking about going to 5.13s with my heavy 33s and then when I get 35s eventually just deal with them on the 5.13 ratio. I have the Rubicon 42RLE tranny

I'd rather have 5.38's with 33's than 5.13's with 35's.
 
I'm pretty that even the 5.13's were not available in thick cut versions until Revolution had them developed at the same time as the 5.38's about 3 years ago. Until then, you had to change the carrier to work with the available thin or regular pattern gear sets.



I'd rather have 5.38's with 33's than 5.13's with 35's.

Oh interesting ok. Even as a DD? I’m ok with the sucky MPG but will that put strain on the drivetrain until I can afford 35s?
 
With the 42rle, 33’s and 5.13 gearing:

View attachment 25566
You have something wrong somewhere. Not sure what, but if you plug those numbers into the calculator and work backwards, it is showing you are running a 34.5" rolling radius on your tires. You should be around 2650 at that speed with 33's. You're showing what you would have with 4.88's, and 33's. Have you corrected the speedo and verified the gear set ratio?
 
You have something wrong somewhere. Not sure what, but if you plug those numbers into the calculator and work backwards, it is showing you are running a 34.5" rolling radius on your tires. You should be around 2650 at that speed with 33's. You're showing what you would have with 4.88's, and 33's. Have you corrected the speedo and verified the gear set ratio?

Now that you say that, I think the shop that did the regear installed a Speedo gear for 35’s. Originally, my plan was to move up to 35’s.
 
Will wonders never cease... I just got back from a quick RT trip to Barstow CA without towing my pop-up trailer and I got 14.34 mpg! And that's on the first half-of my 400 mile trip where I had a climb from my local 340' altitude up to 4000' at the Cajon pass here in SOCAL. My speeds were anywhere from 65-75, I definitely averaged 70 mph the entire way there.

I had never seen over 12 mpg with the 4.88 gears without the trailer. This just goes to prove the theory correct that you can improve your mpg when you raise the engine rpms up enough so the engine isn't lugging.
 
I had never seen over 12 mpg with the 4.88 gears without the trailer. This just goes to prove the theory correct that you can improve your mpg when you raise the engine rpms up enough so the engine isn't lugging.[/QUOTE]

Yep, it's been my experience.
I've owned 2 Chevy Avalanche's , the first had 3.73 gears and consistently averaged 20.1 mpg on highway to work......2nd one has 3.42 gearing and averaging 17.6, same speed, same highway.
Would have never guessed.
 
  • Like
Reactions: DWLJ