37s and drivetrain reliability - is it worth it?

syreeves

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I have a 2021 JTR with Mopar 2In lift and 35s on 17s. No regearing - stock Rubicon gears. 6MT. I debate going to 37s. I could do it with no further suspension mods. But I would definitely want to regear. 35s is bad enough with the 6MT and I am pretty sure 37s would be horrible. What I'm concerned about is drivetrain reliability. I don't rockcrawl but I do hund and drive on muddy and heavily rutted logging roads. Axle and differential clearance is what I'm looking for. I know 37s only give me another inch... But I worry about stress on axles and hubs. And about braking capability with so much added rotating mass. Jeep seems to treat 35s as clearly within factory tolerances for (e.g. extreme recon package ith 35s will be tires and gears but no changes to brakes and axle parts).

What is your experience with 37s - drivability and reliability? Is it really a big difference over 35s? So far I think 35s strike a great balance between reliability, warranty-ability, and overall good looks.

I'm sure this opinion has been debated but now that people have put 30-40K miles potentially on 37s I'm curious about long term livability.

Thanks
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hjdca

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Yes, 37s make a big difference off-road. I 4wheel with gladiators with 35s and a Mopar lift, and my 37s with a 3.5" lift give me a lot more clearance and capabilities. Regarding stress, It is not so much the size, but, the weight of the tires and wheels that stress the drive train. I tried to go as light as possible, ie. 26 lbs wheels (method Bead grip) with 71 lbs tires at 37 inches (Goodyear Kevlar MTR). I have my setup now for almost 1 year with 15K miles and lots of off-roading. I also did badge of honor trail - Gold Mountain. No issues at all, and I am running 5:13 gears on my manual Rubicon, granny gear locked up really tracks like a tank over everything. I have the wheels and tires balanced and rotated every 5K milies at Discount/America's tire. This is very important with 37s or you may not like your tires after 10K miles....
So, if you want 37s, and you are worried about driveline stress, go as light as possible on the wheels and tires, install the right gears, get the tires balanced and rotated for free every 5K miles, and you will be there for the win !
 

ranger5oh

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I don't really see how running 37's is much different on a drivetrain than towing a light load. I am running 37" KO2s on stock 4.10s (automatic trans), and it feels basically stock to me. I am not an aggressive driver, and generally accelerate and brake moderately.

There are plenty of jeeps out there that have been running 37s for years with no issues. Unless you are doing tons of rock crawling or towing heavy loads, I see no reason why the 37s would be detrimental.
 

rezar1

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Does 37s impact tow capability of the truck? I am planning on putting 37s with 3.5" lift but also planning on towing a camper. I do plan on re-gear to 4.88.
 
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syreeves

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Yes, 37s make a big difference off-road. I 4wheel with gladiators with 35s and a Mopar lift, and my 37s with a 3.5" lift give me a lot more clearance and capabilities. Regarding stress, It is not so much the size, but, the weight of the tires and wheels that stress the drive train. I tried to go as light as possible, ie. 26 lbs wheels (method Bead grip) with 71 lbs tires at 37 inches (Goodyear Kevlar MTR). I have my setup now for almost 1 year with 15K miles and lots of off-roading. I also did badge of honor trail - Gold Mountain. No issues at all, and I am running 5:13 gears on my manual Rubicon, granny gear locked up really tracks like a tank over everything. I have the wheels and tires balanced and rotated every 5K milies at Discount/America's tire. This is very important with 37s or you may not like your tires after 10K miles....
So, if you want 37s, and you are worried about driveline stress, go as light as possible on the wheels and tires, install the right gears, get the tires balanced and rotated for free every 5K miles, and you will be there for the win !
Thanks - I am balancing my 35s every 7K miles. And totally hear you on rotating mass. Thank you!
 
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syreeves

syreeves

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Does 37s impact tow capability of the truck? I am planning on putting 37s with 3.5" lift but also planning on towing a camper. I do plan on re-gear to 4.88.
I'm not sure if affects rated tow capacity but certainly without the right re-gear 37s make the stock gearing too tall and towing becomes more difficult. i know that with 35s I routinely need 4th gear to hold a steady 65 with 3500lbs in tow... and i definitely cannot bog in 2nd and 3d- have to shift so that I'm always above 3000rpm for any real acceleration.
 

Mr._Bill

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Does 37s impact tow capability of the truck? I am planning on putting 37s with 3.5" lift but also planning on towing a camper. I do plan on re-gear to 4.88.
Any change to the suspension and tires will affect towing capacity. How much is difficult to say. Weight added by the larger tires, and stability from moving the frame farther away from the axles, are issues to consider. Regearing will help. Unless you plan on towing near capacity, it should not be a problem.
 

kevman65

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Your biggest concerns with running 37's are the ball joints on the knuckles and FAD area of the axle.
Will they fail? Maybe, maybe not. But you are putting more stress on those areas.

You can get aftermarket HD ball joints that use a steel on steel design versus the factory plastic on steel.

You can do a FAD delete and go with a single piece axle shaft on that side. The axle housing is still weaker on this side from basically a hole in the axle housing. You can also truss the entire front axle.

If seriously going to bounce off rocks, ditching the cast aluminum knuckles for forged steel or cast iron versions are also done.

Is any or all of this needed? Again maybe, maybe not. Depends on where you're wheeling, your driving style, and that one uncontrollable, luck.

For on the road only, the only thing I would recommend definitely doing is upgrading to HD ball joints.
 

AMAGladiator

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I’m curious on this as well, as I am in the process of installing a mopar 2” lift, steersmart pro adjustable track bar, synergy adjustable lower control arms and slapping 37’s on stock rubi wheels. Been going back and forth with 35’s or 37’s. So much content out there debating that both are the way to go.
 

bleda2002

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As someone above mentioned, the big wear item will be ball joints, but on heavy 35's those are gonna get worn probably just as quick as 37's. The rest of it should be fine, you're literally talking 1 inch of height difference between 35's and 37's and the factory says 35's are direct bolt on (and offered with the xtreme recon). Cheap insurance is to truss and gusset for about 250 in parts and the cost of a welder.
 

Mac

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So many variations in size and weight with different brands in 35s and 37s, BFG 37s are often the same size and lighter than other brands 35s, so brand will definitely play into the reliability factor for those reasons.
 

WXman

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I would argue that the joints, FAD, axle shafts, etc. aren't going to lose usable life nearly as quickly as that weak a$$ clutch Jeep uses. Running tires that are four inches taller than stock is certainly going to affect the clutch, particularly in gears 4 through 6.
 

exfil offroad

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Is that recommendation based on manual or automatic transmission? Does that matter? Mine is automatic.
automatic transmission. yea i believe it does matter, but not that you cant put 5.13 in it just changes the shifting.
 
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