6 speed gear decision input needed

[azwjowner]

I have 4.56 and 32s, which works out to almost precisely the same ratio as 4.88 and 35s. It's great but 1st is deep and I don't go over 70. It sounds like 4.56 would be optimal for you.

But if you have 4.10 already, I would just leave it and pretend 6th doesn't exist. Even a regear won't quite fix the gap between 4th and 5th/6th. When I downshift from 6th, it's always to 4th. You're not going to downshift from 6th to 5th even if you regear to 4.88.

5.13 would absolutely be a mistake for you at 75 mph. Much too high RPMs for cruising.

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[GabeBoyTheGreat]

no way 2500 at 75mph with 4.88s and 35's I run 4.88 and 37's at 2650 at 75mph

Not in 6th gear unless your speedometer is off.

 

[GabeBoyTheGreat]

But if you have 4.10 already, I would just leave it and pretend 6th doesn't exist. Even a regear won't quite fix the gap between 4th and 5th/6th. When I downshift from 6th, it's always to 4th. You're not going to downshift from 6th to 5th even if you regear to 4.88.

I don't know that I agree with that. At 75 MPH, here are the RPMs for the different configurations:

1. 4.88s, 5th gear - 2,850 RPM
2. 4.10s, 4th gear - 2,950 RPM

#2 has a slight power advantage over #1, but just barely. #1 and #2 will be very similar for most scenarios, but the advantage of #1 is that you still have 4th gear to downshift to if need be. In the #2 scenario, you are already in 4th gear.

 

[roaniecowpony]

It’s more trying to get it to where I can drop down to 5th for the hills instead of dropping to 4th which is a bigger step. I’d really like to get some mileage back too if I can, that 11.5mpg kinda stung

Sounds like that 11.5mpg was the wind?

 

[Maverick909]

Not in 6th gear unless your speedometer is off.

if my speedo was off id be going into limp mode

 

[GabeBoyTheGreat]

if my speedo was off id be going into limp mode

The tachometer needle might be slightly off then.

 

[jbcrane]

I’m about to get my wife’s Jeep regeared. Hers is also a 6 speed but a sport. Her Sport has my original Rubi axles under it with the stock 4.10’s. We recently did a small lift and 35x12.5-17 tires on my original Rubi wheels. Hers will never go bigger than 35’s and the 4.10’s just don’t cut it on the highway. We recently went to OKC from Amarillo and was in 5th pretty much the entire just to be able to go the speed limit of 75. 6th couldn’t maintain that speed even on flat road.

Those that have 35’s on a 6 speed, 4.88 or 5.13? I’m leaning towards 4.88 for the bigger pinion, but that’s not a huge deal on hers it’ll see some dirt roads and light trail use

I'm by no means an expert and had the same question several years ago, but between 4.56 and 4.88's. After a lot of hemming and hawing went with 4.88's and am so glad I did. He's a Jack Rabbit on 35's... plenty of power, even at altitude here in Colorado. 5.13's would be awfully short in 1st and 2nd. Even with 4.88's I worry about getting rear-ended by the youngster behind me not paying attention. And like you said, there's the pinion size and smaller teeth on the ring gear too.

 

[jbcrane]

5.13 would absolutely be a mistake for you at 75 mph. Much too high RPMs for cruising.

I would agree with this.

 

[Oletimer]

Did you still start in 1st? Or did you jump to 2nd??

both, it took off in second just fine. I f i was pulling out into traffic I skipped first.

 

[CorvZ061]

We decided we’re going 4.88’s

 

[alphawolff]

I’m about to get my wife’s Jeep regeared. Hers is also a 6 speed but a sport. Her Sport has my original Rubi axles under it with the stock 4.10’s. We recently did a small lift and 35x12.5-17 tires on my original Rubi wheels. Hers will never go bigger than 35’s and the 4.10’s just don’t cut it on the highway. We recently went to OKC from Amarillo and was in 5th pretty much the entire just to be able to go the speed limit of 75. 6th couldn’t maintain that speed even on flat road.

Those that have 35’s on a 6 speed, 4.88 or 5.13? I’m leaning towards 4.88 for the bigger pinion, but that’s not a huge deal on hers it’ll see some dirt roads and light trail use

4.88s on 35s with the manual in the JL is god's paradise. do it.

 

[Scott97]

We decided we’re going 4.88’s

You made the right choice and will not regret it. I regeared to 4.88 about 3 months ago, running true to size 35s (not 34.5") with the 6MT. Very happy with the result.

Lots of posts about first gear being a little short and 2500RPM at 75MPH both are true and really not a big deal. Where the 4.88 gears really shine is on secondary roads with hills, 45-70MPH. In this scenario, it is all about available torque from the 3.6 engine and the gear ration spacing. The 3.6 does not start making torque until 1750RPM and is not up on the flat spot of it's torque curve until about 2300RPM. Shifting between 3rd, 4th, 5th can be miserable because of the large ratio spacing between 4th and 3rd. Regearing to 4.88 will put you in a much better place, shifting between 4th, 5th, 6th on secondary roads with hills because these gear ratios are closer together (by a factor of over 2.5), making it a pleasure to row between these three gears and stay up on the engine's torque curve.

Here is to you and your wife enjoying your Jeeps!

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