37s on stock rubicon axles?

rybread30

rybread30

New member
I need new tires and want to go to 37s, would it be better to stay with 35s and build the axle and then get 37s or will the jeep be okay if I throw on the 37s and build it as with the 37 on there?


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rybread30 said:
Forgot to add,
How much power will I lose?
Gas mileage loss?
What is most prone to fail?
Click to expand...

If you're running 4.10's, it's tolerable. If you're running 3.73's, you're gonna want to re-gear as the power loss is considerable.

Regarding MPG, you drive a brick in the wind and now you're adding bigger tires with more rolling resistance. Re-gearing will help mitigate your loss but there will be a loss.

As far as failure goes, you're likely to bend your rear axle shaft flanges, bend your front axle even with gussets, sleeves, truss or what have you and that will lead to a front axle seal leak. If you play hard enough, you will most likely break a driver side front axle shaft and if you have factory e-lockers, you will trash them as well.
 
Mike_JK_Houston_711 said:
You'll be fine as long as you don't beat the hell out of it. But C gussets and stronger axle shafts should be on your SHORT list of mods.
Click to expand...

x2 - ran 37's on my stock D44, seems I was actually more careful on when I used my front locker and also tried to pick better lines as not to beat the hell out of it
 
If you haven't regeared yet, 37s will make your Jeep a bigger dog than they already are. C gussets, aftermarket chromoly axle shafts and regear you will most definitely want to do if you're going straight to 37s.
 
The biggest issue around here will be power loss in the hills. So then you're going to want to regear to fix that. Regearing runs about 1500ish, so if you're going to upgrade the axle for sure in the future, I would do the regear then so you don't spend money twice. And until you re-gear, power will go down. MPG will go down no matter how you look at it. There's pros/cons with MPG and re-gearing. Some driving conditions will actually help your mpg and some won't. Modified Jeeps and MPG don't really go together anyways.
 
I'm putting 37s on in the next week or so. Only doing C gussets for now. I'll wait till I break a shaft before I replace with chromoly. Ideally it lasts for 3-4 years and then I get Dynatrac axles.
 
rybread30 said:
Forgot to add,
How much power will I lose?
Gas mileage loss?
What is most prone to fail?




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Click to expand...

you'll feel the loss of power depending on what your gearing is

mileage? lol I quit thinking about mileage since the 1st Jeep I owned. if you're concerned about mileage don't get 37's

with 37's 4.88 gears, super tuner running aftermarket coil and wider gap on plugs, 93octane... worst 9mpg, best 17mpg I think I had a tailwind lol, avg around 13mpg but also depends on how much I'm loaded down.

failures depends on how you drive. if you keep your stock steering, possibly sector shaft plus what Eddie mentioned.

IMO 37's also require more maintenance than regular oil changes, I change out my differential oil, transmission fluid and coolant once a year. unless I'm driving it hard and towing a lot more than normal then i'll change out trans and diffs after 6 months.

IMO burnt fluids lead to premature failure, cheap insurance to drain and change.
 
rybread30 said:
Forgot to add,
How much power will I lose?
Gas mileage loss?
What is most prone to fail?




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Click to expand...
I ran 37" KM2s on my 08 rubi unlimited 6 speed with 4.10s in Colorado.

The power loss wasn't miserable but noticeable for sure, not fun getting passed by semi trucks on a freeway grade haha.

Gas mileage I averaged around 10 in town 15 highway (no wind) but as stated before I didn't really care it's a jeep.

As far as breaks I had the rubi front axle with stock shafts stock e locker added C gussets and sleeves (I know I know I got talked into them early). I managed not to break the shafts or locker however the stock ball joints will be trashed really quick and possibly unit bearings, not sure I never checked mine. I also developed an inner axle seal leak wich may or may not have been a bent tube once again never checked before it got sold.
In the rear it was bone stock no mods and nothing broke.

I wouldn't say I babied my rig off road but by no means would I say I beat on it just a nice middle ground and I managed to make most the stock stuff last and still have fun. The 4-1 the case really helps off set the gear issue when off road of your using Low range but my 4hi sucked

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I wheel with a guy who has completely stock rubi axles running 37" trail grapplers and he does much gnarlier shit than I will attempt at the moment.

I spotted him through the little sluice obstacle at Truck Haven and saw both axles take a beating through there... Really impressed how they faired, the only thing that took a loss was his front diff cover getting bashed by the tie rod.

I would gusset the c's if it were me and upgrade the diff cover to something more durable on the front and just upgrade the axle shafts in the rear if your budget allows.
 
Don't Forget the Brakes!

I would highly suggest you look at upgrading your brake components as well. With 37's in 4-low and 4.88 gears, I could barely keep the Jeep from moving forward down hill standing on the pedal with both feet.

I'll throw in a shameless plug for Dynatrac's Progrip kit. Much more confidence in stopping now.
 
rybread30 said:
I need new tires and want to go to 37s, would it be better to stay with 35s and build the axle and then get 37s or will the jeep be okay if I throw on the 37s and build it as with the 37 on there?


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Click to expand...

Welcome to WAL :standing wave:

I have been running 37s on my stock 44 axle housing (w/ C-gussets) for about 2 years or so. YES it is not ideal, YES i worry about it all the time. No, I dont drive fast off road... YES, I AM scared of pot holes. YES, I slow down for speedbumps, YES I will be upgrading to a PR housing in the near future. :thankyou:


wayoflife said:
If you play hard enough, you will most likely break a driver side front axle shaft and if you have factory e-lockers, you will trash them as well.
Click to expand...

Says the mall crawler that ran stock front axle shafts in rubicat up until recently; and IIRC, is STILL on the factory front Rubicon locker? :hmm: :cheesy:
 
I did 35's on my 4.10 gears it was fine out of the 07 3.8. I switched 37s and I had to slip the clutch like crazy to drive. It was a turd to drive. I'm in the middle of a 5.13 gear swap break in and it drives great. Acceleration is nice and I barely slip the clutch. I wouldn't recommend 37s without regearing, it sucks. I haven't tested the Mpg.
 
rybread30 said:
Forgot to add,
How much power will I lose?
Gas mileage loss?
What is most prone to fail?




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Click to expand...

It looks like a lot of great advice has been given here. Just to echo what others have said... you'll want to regear I'm runnning 37's on stock axles and regeared to 5:13's it made a big difference in terms of power loss. I get 16 mpg. As far as prone to fail I feel it depends on how hard you wheel. I'd also consider doing the progrips we love ours. [emoji482]


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For what it's worth, I drove a 2017 3.6 L JKU Sport with 37's and a lot of heavy upgrades, bumpers, sliders etc. gears were 3:73 with auto. Around town drive ok, on the interstate the thing was a DOG! Set cruise and on small grade hills the auto was hunting for a comfortable gear, and could only maintain 50-55mph. In the flats cruising at 70 mph was ok. I checked MPG and corrected odometer with flash pack dealer installed said 14mpg in the 200 miles it had been driven.

No doubt out of all the threads I've read here and those other inferior sites, regear is a must. My buds with 35's and 3:73's hate me on the interstate mountains of east Tn when I blow by with cruise on 75mph (I have stock 32's and 4:10s) Then you have to think about all the other additions upgraded axles shafts, upgraded lockers, etc. and you have to think is it worth it without going full dynotrac rebuild.

For me I would love to run 37's but I will run 35's for a couple of years. My rig is new and don't want a mall crawler, I want to have fun on the trails. IMOP I would run 35's, regear , and put the money into a really good suspension lift like Evo coil-overs, do your body armor, and ready the rig for eventual major upgrade. Right now I can't see going half way on a new rig that is fun in stock form, and would be really fun with a mild less expensive build. Max I'm going to do with stock 4:10 ruby axles is regear, steering, brakes, and carry some extra axles shafts.

That's my 2 pennies worth


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What all this really boils down to are those damn WAYALIFE awesome videos with RubiCat and Moby... the green monster comes out... I want I want!! I will get there because my bucket list wish is to eventually ride with those guys! Is it really just the "Tennessee Honey" though??

PS the extra periods do not mean I am confused, I'm just thinking. [emoji106]


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rybread30 said:
I need new tires and want to go to 37s, would it be better to stay with 35s and build the axle and then get 37s or will the jeep be okay if I throw on the 37s and build it as with the 37 on there?


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Click to expand...

If you're just driving around on flat ground at see level and wheeling moderately you'd likely not have problem starting with the 37" tire then building up the axles. I wouldn't wait for ever to do so.

If you wheel pretty hard and/or live at altitude in hilly or mountainous terrain I'd consider doing the axles first and adding the 37s later.

Either way if you know 37s are the end game and you wheel fairly regularly you'll want to beef up the front.


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The carrier is really pretty good on the JKUR. Adding 37s would make me think about four things:

1) front axle housing
2) front and rear axle shafts
3) front and rear brakes
4) ring and pinion gearing


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