37s No regear question

[SCLaunch]

One day I'm ready to pull the trigger on 35s and the next I'm back to 37s.

I see a lot of threads saying don't dare go 37s without a regear. Then also others saying no problem.

This is a daily driver, so the question is how hard on the transmission and engine are 37s really? Is it worth the concern? Thanks!

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[kevman65]

3.73 or 4.10 ?

Makes a difference.

 

[JustinLentz]

I ran 37's with no regear for 2years with no problem. If you have an auto, you will never see 8th gear. I reprogrammed for the 37's but never did the regear. I had 4.10's already.

 

[SCLaunch]

3.73 or 4.10 ?

Makes a difference.

Rubi, so 4.10 currently

 

[HooliganActual]

One day I'm ready to pull the trigger on 35s and the next I'm back to 37s.

I see a lot of threads saying don't dare go 37s without a regear. Then also others saying no problem.

This is a daily driver, so the question is how hard on the transmission and engine are 37s really? Is it worth the concern? Thanks!

The real issue with 37's on stock gears is that you may not be as quick off the line as you would be with bigger gears and you may not see 7/8th gear out on the highway and thus your MPG will be worse.

EDIT: your crawl ratio can suffer but I have never had a problem wheeling the cr@p out of mine.

Bigger tires are harder on everything but not worse because you didn't re-gear.

I've been on 37's with 4.10's as @JustinLentz was saying he is and i have a big phat rig that has scaled at 6200# and I still occasionally see 8th gear on the open road.

There's no denying that it would be better to re-gear but it is absolutely livable and usable and not detrimental to not re-gear.

 

[kevman65]

Rubi, so 4.10 currently

You'll be fine. MPG will drop, will take longer to get to top speed, you and 8th gear are getting a divorce.

 

[MPMB]

Went to 37s in December. Dropped about 2mpg. Truck tends to hang at higher RPMs longer when getting up to speed.

I can get into 8th gear, but I'm not supposed go that fast with my RTT.

It's not that bad in my area.

 

[Deadpool392]

It all depends, having re-geared to 5.13 on a 2010 JKU for 37’s and now on stock 4.10 and just having added 37 KO2’s, I am not in a hurry to do a re-gear. Everyone’s usage and results will be different, tire/wheel combo weight will play a part, what elevation you live at, etc. I only have about 100 miles on my 37’s, but I am getting the same mileage as I was on the 35 KO2’s where I live. I may be singing a different tune after my summer trip to Moab.

 

[JTGuy]

I ran 315s with 4.10s for a while and it was OK. I finally went to 37s and they were oK with the 4.10 but went to 4.88s and it's just a perfect match. My tires were BFG KOs so light and not true 37s. I have no regrets.

 

[Kajo]

I think the weight of the tire and wheel combo make a difference. I have run 37" KO2s on stock rims with 4.10s for two years, including a trip from Maryland to Moab, Utah and am happy with the setup. I have seen some 37" wheel/tire combos ending up 40+ pounds heavier than my set up per corner and no doubt that difference in rotating mass would effect the vehicles performance.

 

[camodog]

Just get the 37s and see how it goes.
I live in the Rockies, have had 37s since day 1 and have never had an issue.
I do see 8th gear from time to time.
I will eventually regear, but I don’t think it’s as bad as some make it seem

 

[Reddout99]

Everyone is is always mentioning 8th gear. Can't you just manually shift into 8th if you're traveling down the highway for a stretch?
8th gear isn't a deal breaker for me. I'm going to try the manual shifting to 8th on a road trip across country later this year. Long stretches of flat highway on interstate 80 heading west.
I'm on 37s in a Sport S with 3.73s. mine is a daily like yours I have zero issues. I did reprogram for the bigger tires though

 

[TheRealGinjaNinja]

Everyone is is always mentioning 8th gear. Can't you just manually shift into 8th if you're traveling down the highway for a stretch?
8th gear isn't a deal breaker for me. I'm going to try the manual shifting to 8th on a road trip across country later this year. Long stretches of flat highway on interstate 80 heading west.
I'm on 37s in a Sport S with 3.73s. mine is a daily like yours I have zero issues. I did reprogram for the bigger tires though

The motor is pretty gutless from a torque perspective. Anything under 2100 rpms at cruising speeds it won’t be able to maintain. I travel 1200 feet to sea level elevation daily. I went from 35s / 4.10s -> 37s / 4.10s -> 37s / 5.38s.

35s with stock gearing and 8 speed auto wasn’t that horrible but far from ideal. My opinion is we don’t have enough gear for factory tires.

37s and stock gearing you can live with but it really doesn’t drive/shift all that great without manually shifting. Even with manually shifting the lack of torque is annoying. 7th gear is barely usable and 8th only downhill. My suggestion is if you 100% know 37”+ tires will be permanent, regear with 5.13s or 5.38s. My 5.38s are amazing and perfect for it.

Cheers

 

[MPMB]

Everyone is is always mentioning 8th gear. Can't you just manually shift into 8th if you're traveling down the highway for a stretch?
8th gear isn't a deal breaker for me. I'm going to try the manual shifting to 8th on a road trip across country later this year. Long stretches of flat highway on interstate 80 heading west.
I'm on 37s in a Sport S with 3.73s. mine is a daily like yours I have zero issues. I did reprogram for the bigger tires though

For most driving, that solution won't work.

I shifted into 8th coming home from Jackson, WY on roads in farm valleys and the RPMs are so low it's out of the acceptable power band to maintain speed. A JT can only go so fast with the aerodynamics and aftermarket parts on it.

To go at a speed where the truck stays in 8th gear, I (along with most who have a ton of gear on the truck) am looking at maintaining 80-85mph (estimated, someone can probably do the math).

I've shifted to 8th and tried going uphill, and even past 1/2 throttle, there's not enough HP/TQ to maintain or increase speed at 65-70mph. So on a long road trip, you'll end up slowing going even slightly uphill or using more gas to keep the speed up in 8th.

I can't remember off the top of my head, but I think at 70mph, 8th gear runs at about 1600rpm, maybe 1700.

 

[jwilson2899]

I think the weight of the tire and wheel combo make a difference. I have run 37" KO2s on stock rims with 4.10s for two years, including a trip from Maryland to Moab, Utah and am happy with the setup. I have seen some 37" wheel/tire combos ending up 40+ pounds heavier than my set up per corner and no doubt that difference in rotating mass would effect the vehicles performance.

^^^^ this x1000

I had a very extensive conversation with @Kajo after seeing a couple of his posts about 37's and 4.10, mainly based on the fact that we live close to each other and have travelled the same roads, so it was a good comparison. Based on those chats, I pulled the trigger last fall on 37" KO2s for my Rubicon and have not regeared. Because of the lower weight of them vs my E rated 35's I had before. I really don't feel any power difference in the truck and it actually gets better mileage than it did on 35's. I also see 8th gear all the time with it while driving on the highway, so at this point I'm going to keep riding with these and not do the regear.

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