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Discussion Starter · #1 ·
I recently purchased a 2017 JKU and starting my build and was wondering with a pro comp 4" lift can I put some 37/13.50/20 on my jeep and not change the gears or driveshaft out?
 

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I've got 35s and the 4.1 gears on my '15 JKUR.

No way I'd put 37s on stock, it's a dog now with the 35s.
 

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Short answer yes it will drive but you will learn to hate it real quick. I have 3.5 inch lift and 37's with 4.56 gears and I'm happy. When I had 3.21's I was not happy but it drove.
 

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I just swapped factory 4.10's for 5.13's running 37" KO2's.

4.10's was doable. Actually really good on the open highway. Kinda sluggish around town. I was a little concerned of the long term effect in the tranny.

Drive shafts will depend on your angles. I am sitting at about 4" - 4.25" above stock. Still running stock drive shafts. The front CV seems ok so far. The slip boot can make contact with the exhaust. I am about 10k mikes in. New driveshafts are on the radar.
 

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Depends on what gears you currently have. I drove a year with 4.10 and 37x13.5x17, then went 4.88. Huge difference! I wouldn't do it with 3.73 or 3.21 gears.

Rear axle shaft flanges bent fairly quick and had to be replaced. Followed by ball joints, unit bearings, track bar, front drive shaft, drag link end and tie rod ends. Make sure you add C gussets at a minimum.

Always a good idea to add bigger brakes.

Good luck! :thumb:
 

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Discussion Starter · #6 ·
It's 3:73 when I looked on the sticker, I do think I'll more than likely go with 35s to be on the safe side bc my build is already at like 12k and don't wanna dump too much more in it now ?
 

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Choose gears and tire sizes carefully and to match your driving style and conditions

I recently purchased a 2017 JKU and starting my build and was wondering with a pro comp 4" lift can I put some 37/13.50/20 on my jeep and not change the gears or driveshaft out?
Those tires are a bit too big for 4.10's (if you have them), same for 3.73 etc.

Please see these charts on Wandering Trail Jeep blog

This practical, informative Jeep blog (link below) was shared in another WF thread and has a useful JK gear/tranny/tire size (diameter) chart that addresses the various JK gear, transmission, and tire options from these perspectives:

- Performance (~acceleration/works well)
- Acceptable (~what works/is good/OK)
- Minimum (~possibly sub-par performance)

Chart Link: Jeep Wrangler JK Gear Ratios
(wandering trail mechanical gear ratio charts)

Choose/review the correct chart with your:

(a) engine size 3.8L or 3.6L
(b) transmission manual or 5-spd auto
(c) tire diameter - actual or desired/planned.

The charts even list the gear ratios.

Charts covers tire sized from 29" through 44" and gears from 3.21 through 7.17 (3.21, 3.73, 4.1, 4.56, 4.88, 5.13, 5.38, 5.86, 6.17, 6.5, 7.17).

Note/caveats: The actual use of your Jeep (commuting, recreation, on-road, off-road, rock, trail, mud, flats, etc.), other equipment, terrain, weather conditions, speed, acceleration and braking demands and expectations, and driving style also determine your perception of your driving experience/ performance - with respect to engine, transmission, gears, and tire diameters.
 

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i had 37's on 3.73's for about 5 months, then i installed 4.88's. was a nice improvement and i can now use 5th and 6th again. if i had to do it over again, i would without a doubt go 5.13's!
 

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How are you at 12k without driveshafts or gears.
I am also quite curious about this.

Gears should be done when you install the tires. I wouldn't run either 35s or 37s on 3.73. Stick to stock size tires until you can budget a regear.
 

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I also would not do a 4 inch lift, or a Procomp lift. Read around here for a while before you do anything. Or do you already have the lift on? 4 inches is too steep for stock driveline - stock driveshafts will not last long at all.
 

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Discussion Starter · #13 ·
My build will include rims and tires 35/12.5/20, front and rear bumper with 4-4" led lights and a 20" light bar in the front bumper as well as 12k lbs warn winch, nerf nab adujistable side steps(for the wife lol), 4" inch pro comp lift, toggle pillars switch, bushwacker fender flares, under jeep led light kit, speedo for calibration...total was 11,630 everything installed and tax ??
 

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How are you at 12k without driveshafts or gears.
I am also quite curious about this.

Gears should be done when you install the tires. I wouldn't run either 35s or 37s on 3.73. Stick to stock size tires until you can budget a regear.

Ha. I was going to say because of lights and now that's confirmed by OP

Personally I'd focus on driveline and not worry about lights until I reach some point where I am actually having difficulty seeing on night trail runs.
 

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My build will include rims and tires 35/12.5/20, front and rear bumper with 4-4" led lights and a 20" light bar in the front bumper as well as 12k lbs warn winch, nerf nab adujistable side steps(for the wife lol), 4" inch pro comp lift, toggle pillars switch, bushwacker fender flares, under jeep led light kit, speedo for calibration...total was 11,630 everything installed and tax ??


Purchase through our vendors here in WF. No tax, discounted products, and free shipping. Your going to need a regear. Forget the lights for now and fender flares...use that for regear. Also the 4" pro Comp isn't recommended since it's incomplete and your going to need more parts to do it right.
 

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And my sticker says 3:21 gear so more reason I should change it with the build?
My build will include rims and tires 35/12.5/20, front and rear bumper with 4-4" led lights and a 20" light bar in the front bumper as well as 12k lbs warn winch, nerf nab adujistable side steps(for the wife lol), 4" inch pro comp lift, toggle pillars switch, bushwacker fender flares, under jeep led light kit, speedo for calibration...total was 11,630 everything installed and tax ??
Focus on mechanicals FIRST. Fancy bumpers and lights won't get you home. Regear should be priority one with tires and lift. The rest can wait.
 

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My build will include rims and tires 35/12.5/20, front and rear bumper with 4-4" led lights and a 20" light bar in the front bumper as well as 12k lbs warn winch, nerf nab adujistable side steps(for the wife lol), 4" inch pro comp lift, toggle pillars switch, bushwacker fender flares, under jeep led light kit, speedo for calibration...total was 11,630 everything installed and tax ??
IMO 4" and flat fenders will look pretty goofy, too much fender space for a 35" tire. I've been happy with 2.5" on 35's, might go 2.5" and flat fenders on the next one. Also a lower lift will ride/drive better without spending a ton of money to make it right.

I'm not familiar with that side step, when I was new I bought the wrong side steps, had to buy them again. Make sure they're smooth enough and strong enough to slide on the rocks and still protect you.

As far as front lights about the only time you use them is leading a night time run, no one wants the Jeep behind them blinding them and they're illegal on-road. I'd add those once you've completed the rest of your items.

Making an assumption here, visit another shop (besides 4WP judged by your parts list) and see what they recommend. Nothing wrong with 4WP but they usually push the product with the best profit for them, not the best product for your Jeep.

Lastly, you can save a lot of money and learn a lot about your Jeep by installing yourself, at least consider it :)

Good luck! :thumb:
 

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What are you building your jeep for?
Only ask because of your build list sounds like top down door off beach cruiser
If so, gears are not really needed for 35's. My current jeep runs 35's/3.73's turns them just fine for the off-roading I do
My jeep my ex wife has runs 35's/3.21 and it does alright off-road
Lift kits still relate to what you want to do, heavy rock crawl go with the bigger names/higher end kits. Just building a cool street jeep then the lower RC/superlift/procomp kits will do the trick. Just ditch the drop pitman arms for a high steer drag link
Had one friend had a street jeep that he ran a teraflex 2.5 plus a budget boost added on top. I thought it would be the sketchiest thing ever but since he just cruised the streets with it it did quite well lol
You can also save a few bucks by dumping the warn, especially if your not planning a heavy rock crawler. They are horribly over priced and over rated. Smittybilt makes a nice winch for a fraction of the price


Sent from my iPhone using Tapatalk
 

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I have 3.73 on my current (3.6/6spd/4dr/35's). I also added about 550lbs of additional goodies and I'm planning to add about 100 more (roof rack) as my end goal.

Yes it will move, but I feel as if my jeep is driving on an incline. 1st gear will need somewhat of rev and clutch management especially on slight grades from a stop. I'm scheduled for regear next month. I wanna limit the strain on everything and have more torque especially in lower gear.
 
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