Re-gearing

[Adagusti]

Hey sorry I am sure people talked about it heaps but I am about to put the trigger.
So I have a 2 inch lift 33 tires with spacer. 5 speed Manual. I don’t 4wd it’s just my daily driver but I have 3.07 gear atm and uphill it’s a nightmare but except from that it’s ok.
Should I go 4.10 or 4.56 I am worry 4.56 it’s too much.
Thanks

 

[JMT]

Hey sorry I am sure people talked about it heaps but I am about to put the trigger.
So I have a 2 inch lift 33 tires with spacer. 5 speed Manual. I don’t 4wd it’s just my daily driver but I have 3.07 gear atm and uphill it’s a nightmare but except from that it’s ok.
Should I go 4.10 or 4.56 I am worry 4.56 it’s too much.
Thanks

4.88

 

[machoheadgames]

Most are going to tell you to go with neither of those and to go with 4.88 instead…myself included.

 

[Adagusti]

Most are going to tell you to go with neither of those and to go with 4.88 instead…myself included.

Really? Even if I don’t do any 4wd and if 3.07 isn’t that bad atm except uphill?

 

[Chris]

4.88

 

[jjvw]

488

 

[GoldenGorilla]

I am not going to join most. The driveshaft rotation speed with 4.88s with 33s at highway speeds is going to exceed the speeds most shops can balance at. I raan 4.10s with either true 33s or 32.6" tires for 20 years before switching to 4.56 and I looked at the GrimmJeeper gear calculator to figure out what would best suit my needs.

https://www.grimmjeeper.com/gears.html

In 5th gear at 75mph the engine rpm is around 2900rpm while driveshaft speed is 3300rpm. with 4.56. They were 10% lower with 4.10s.

I live at the foot of the Rockies and while it is overall working much better with 4.56s, the only place I really needed them was the steep last pitch up to the tunnel at almost 12,000ft on I-70 where I couldn't hold 50mph in 4th. I've done some other performance mods at the same time and am now holding over 62mph actual though the same area.

 

[jjvw]

I am not going to join most. The driveshaft rotation speed with 4.88s with 33s at highway speeds is going to exceed the speeds most shops can balance at. I raan 4.10s with either true 33s or 32.6" tires for 20 years before switching to 4.56 and I looked at the GrimmJeeper gear calculator to figure out what would best suit my needs.

https://www.grimmjeeper.com/gears.html

In 5th gear at 75mph the engine rpm is around 2900rpm while driveshaft speed is 3300rpm. with 4.56. They were 10% lower with 4.10s.

I live at the foot of the Rockies and while it is overall working much better with 4.56s, the only place I really needed them was the steep last pitch up to the tunnel at almost 12,000ft on I-70 where I couldn't hold 50mph in 4th. I've done some other performance mods at the same time and am now holding over 62mph actual though the same area.

I live here too. I daily drove 4.88, 5 speed on 33s for over 100k miles all around Colorado and neighboring states. There is no way I would ever want anything less than 4.88 with that combination. Driveshaft speeds were a non-issue. Maintaining highway speeds on I70 was a non-issue, except for the tunnels.

 

[mrblaine]

I am not going to join most. The driveshaft rotation speed with 4.88s with 33s at highway speeds is going to exceed the speeds most shops can balance at. I raan 4.10s with either true 33s or 32.6" tires for 20 years before switching to 4.56 and I looked at the GrimmJeeper gear calculator to figure out what would best suit my needs.

https://www.grimmjeeper.com/gears.html

In 5th gear at 75mph the engine rpm is around 2900rpm while driveshaft speed is 3300rpm. with 4.56. They were 10% lower with 4.10s.

I live at the foot of the Rockies and while it is overall working much better with 4.56s, the only place I really needed them was the steep last pitch up to the tunnel at almost 12,000ft on I-70 where I couldn't hold 50mph in 4th. I've done some other performance mods at the same time and am now holding over 62mph actual though the same area.

What is the driveshaft speed at 75 with 5.38's on 35's?

 

[mrblaine]

Really? Even if I don’t do any 4wd and if 3.07 isn’t that bad atm except uphill?

Your complaint is how it works offroad, your complaint is how it works onroad, up hills. Build for that. As for your "isn't that bad" BS, how do you know how bad it really is if you haven't run any other option?

 

[GoldenGorilla]

What is the driveshaft speed at 75 with 5.38's on 35's?

It is whatever your engine rpm is in your 1:1 gear. 4th in a NV3550 or AX-15. If the tire is actually 35" you'll be at apx 3875rpm according to the calculator.

Most driveshaft shops ie Tom Woods and my local shop can balance to 3600rpm. There are some race performance shops that can go up much higher.

 

[mrblaine]

It is whatever your engine rpm is in your 1:1 gear. 4th in a NV3550 or AX-15. If the tire is actually 35" you'll be at apx 3875rpm according to the calculator.

Using your logic then, how are we ever able to run that combo?

 

[machoheadgames]

The driveshaft rotation speed with 4.88s with 33s at highway speeds is going to exceed the speeds most shops can balance at.

The factory was willing to run 4.11 gears witj 27” tires on the 4 cylinder model, resulting in 3671 driveshaft rpm at 70.

For the most part, balanced is balanced. Most of the vibrations talked about here are harmonic and not actual imbalances that can’t be fixed because speeds are too high or equipment doesn’t spin them fast enough. Tom Wood’s doesn’t like high driveshaft speeds either but many here are running them at high speeds anyways and for the most part it works okay…aside from weird harmonic issues on many of them that isn’t really related to the actual balance of the shaft.

 

[jjvw]

.... Tom Wood’s doesn’t like high driveshaft speeds either but many here are running them at high speeds anyways and for the most part it works okay.

And many of us are also running them like that at higher ujoint angles than what TW or Spicer suggests. We are compromising lifespan for driveability and performance. In my expirences, if adding another round of ujoint service is the cost for years of good performance, then so be it.

 

[mrblaine]

The factory was willing to run 4.11 gears witj 27” tires on the 4 cylinder model, resulting in 3671 driveshaft rpm at 70.

For the most part, balanced is balanced. Most of the vibrations talked about here are harmonic and not actual imbalances that can’t be fixed because speeds are too high or equipment doesn’t spin them fast enough. Tom Wood’s doesn’t like high driveshaft speeds either but many here are running them at high speeds anyways and for the most part it works okay…aside from weird harmonic issues on many of them that isn’t really related to the actual balance of the shaft.

High shaft speeds are problematic. They are not good for durability and cause more wear, but everything we do to these things is based around excessive wear and tear and slowing that down with better, stronger, or more suitable parts.

 

[MBDIAGMAN]

OP, maybe I missed it, but what engine do you have?

 

[machoheadgames]

And many of us are also running them like that at higher ujoint angles than what TW or Spicer suggests. We are compromising lifespan for driveability and performance. In my expirences, if adding another round of ujoint service is the cost for years of good performance, then so be it.

High shaft speeds are problematic. They are not good for durability and cause more wear, but everything we do to these things is based around excessive wear and tear and slowing that down with better, stronger, or more suitable parts.

I’m aware and I agree. The stock shaft handling high speeds is a bit different than a double cardan shaft doing the same. But there’s not much we can do about it anyways. To me it’s not worth choosing 4.56 over 4.88 for that reason anyways.

 

[GoldenGorilla]

I didn't say it wouldn't run. You'll only have an issue if the shaft has any imbalance on the top end as it's tough to find a shop that can spin one that fast to address it. To your point, higher speeds, higher angles, everything we do is tougher on the driveshafts and pretty much everything else on the jeep.

Gears are a personal choice and there isn't one right answer. For me, I'd rather the engine rpm be a bit lower if it's still in a range that will perform. I knew my jeep well before deciding to do the gears and the specific problem I wanted to address. It wasn't having a problem holding the speed limit on 4.10s most of the time. The RPM was too low in 4th to make the power I needed to hold the speed limit in a specific place I travel. The 4.56 and 4.88 ratios both brought the rpm back up where I knew it would make enough power. I also looked at the highway cruising rpm at 70, 80 and 85mph which are the speed limits in the states I live in and surrounding and decided the 4.88 ratio would have me at a higher engine rpm than I'd want to be at. Everybody's choices can be different. I'd question the sanity of someone staying on 3.07s with 35s, but if they like being a rolling roadblock, cool.

It's not some magic math. The later JK/JL Rubi owners seem to be totally fine on 4.10s with 33s and many are happy with 35s because the engines produce more power. Most of the LJR 6 speed owners on 33s don't seem to feel the need to change out from the 4.10s because the gear ratio options are better in the NSG370 (unless they crap out). Everyone says the 4.0L is great for low end torque. Obviously it's underpowered.

 

[mrblaine]

It's not some magic math. The later JK/JL Rubi owners seem to be totally fine on 4.10s with 33s and many are happy with 35s because the engines produce more power. Most of the LJR 6 speed owners on 33s don't seem to feel the need to change out from the 4.10s because the gear ratio options are better in the NSG370 (unless they crap out). Everyone says the 4.0L is great for low end torque. Obviously it's underpowered.

That's like saying the rigs with LS swaps don't care because they have enough horsepower to deal with it. Not relevant.

 

[cmoore]

I recommend 4.88s. It’s a common and proven tire/gear recipe.