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Discussion Starter · #1 ·
I'm considering making the leap to 37's in the next year once these 33's knee replaced, but want to make sure I know exactly what I need to do in order to handle tires that size.

Right now I've got a 2.5 inch lift and Smittybilt XRC steel fenders, with 3.73 gears.

Will 37's work on a 2.5 inch lift with those fenders? I know I need to re-gear but by how much - this is my daily driver. Anything else that I would need to do before hand?
 

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I'm considering making the leap to 37's in the next year once these 33's knee replaced, but want to make sure I know exactly what I need to do in order to handle tires that size.

Right now I've got a 2.5 inch lift and Smittybilt XRC steel fenders, with 3.73 gears.

Will 37's work on a 2.5 inch lift with those fenders? I know I need to re-gear but by how much - this is my daily driver. Anything else that I would need to do before hand?
4.88 is probably the minimum you would want. I would think you would need a bigger lift but I could be mistaken. Idk how those fenders sit on the wheel well.

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2.5 will work as long as you have no fenders, flat fenders, or cut fenders. 4.88s would probably be the gear of choice too. If you have d30 front an axle truss, welded in Cs, and new balljoints too.
 

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I would suggest going to a 3.5" coil and 28" shocks to add axle drop. You'll want to add 3" of bump stop, so the longer shock will aid in you maintaining the ability to articulate similar to your 25" shock that you are likely running now while giving up that 3" of up travel. If you just add the 3" bump with your spring and shock set up, you will decrease axle articulation and decrease performance.

4.88 gears with the 3.6L Pentastar work great. It is a hair bit lower than your 3.73 gears, so it works great on the road with the much heavier tires.

You'll need to make sure that you have the backspace you need to allow it to still turn well and not rub before (near) full lock. Around 3.5" max is what I would recommend. You can get there with new wheels or by adding spacers.

Your drag link will need replaced or need braced by welding on heavy channel. I did the weld on channel. The tie rod will need upgraded or it will bend very easily unless your an on-road only kind of guy. The track bar should be replaced with something stronger as well if it is also still factory.

Depending on the year of Jeep, you may need to cut in the rear wheel well. My 2014 did not need this, a 2013 or older will need it.

If you have Rubi-Rails, you need to chop 1.5" from the rear edges if using factory control arms.

You can upgrade ball joints when your stock ones fail, or jump at it now. You pick the brand... Pro-Steer, Rare Parts (The best) or one of the other brands.

Your brakes will be unhappy, I would recommend a Pro-Grip brake kit from Dynatrac. There are other options as well. You should be thinking of this.

At this point, with the bigger lift and longer shocks your drive shafts need to go away, pick a brand of driveshafts and order those as well as the yokes for them. I went with Adams, but there are many options and all are about the same.

Depending on the year of JK, you may need extended brake lines, you will for sure need brake line drop brackets and E-Brake cable drop over the rear axle.

You'll also need longer sway bar links/disconnects front and rear. I cut the rears and weld in a chunk of bolt. I'm cheap like that.

You'll need some form of rear tire carrier, bumper mounted... or one of the rear door hinge replacement styles.

If you off road on rocks, you'' really want to get a ram assist kit. ******* Ram from West Texas Off-Road or the butt-rape priced PSC ram kit. Or you can go the PSC Big-Balls steering box. Whatever you decide.

I would recommend doing the Synergy track bar and Synergy track bar brace. If you do not do the Ram Assist, add to that the Synergy sector shaft brace. Or don't... you decide on the corners to cut and reliability reduction to accept.

Your wallet, your decisions.

That is a good start.
 
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I would not recommend 37s on a D30 Axle - do you have a non-Rubicon, are you able to swing an aftermarket 44 front axle?
 

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Discussion Starter · #9 ·
I would suggest going to a 3.5" coil and 28" shocks to add axle drop. You'll want to add 3" of bump stop, so the longer shock will aid in you maintaining the ability to articulate similar to your 25" shock that you are likely running now while giving up that 3" of up travel. If you just add the 3" bump with your spring and shock set up, you will decrease axle articulation and decrease performance.

4.88 gears with the 3.6L Pentastar work great. It is a hair bit lower than your 3.73 gears, so it works great on the road with the much heavier tires.

You'll need to make sure that you have the backspace you need to allow it to still turn well and not rub before (near) full lock. Around 3.5" max is what I would recommend. You can get there with new wheels or by adding spacers.

Your drag link will need replaced or need braced by welding on heavy channel. I did the weld on channel. The tie rod will need upgraded or it will bend very easily unless your an on-road only kind of guy. The track bar should be replaced with something stronger as well if it is also still factory.

Depending on the year of Jeep, you may need to cut in the rear wheel well. My 2014 did not need this, a 2013 or older will need it.

If you have Rubi-Rails, you need to chop 1.5" from the rear edges if using factory control arms.

You can upgrade ball joints when your stock ones fail, or jump at it now. You pick the brand... Pro-Steer, Rare Parts (The best) or one of the other brands.

Your brakes will be unhappy, I would recommend a Pro-Grip brake kit from Dynatrac. There are other options as well. You should be thinking of this.

At this point, with the bigger lift and longer shocks your drive shafts need to go away, pick a brand of driveshafts and order those as well as the yokes for them. I went with Adams, but there are many options and all are about the same.

Depending on the year of JK, you may need extended brake lines, you will for sure need brake line drop brackets and E-Brake cable drop over the rear axle.

You'll also need longer sway bar links/disconnects front and rear. I cut the rears and weld in a chunk of bolt. I'm cheap like that.

You'll need some form of rear tire carrier, bumper mounted... or one of the rear door hinge replacement styles.

If you off road on rocks, you'' really want to get a ram assist kit. ******* Ram from West Texas Off-Road or the butt-rape priced PSC ram kit. Or you can go the PSC Big-Balls steering box. Whatever you decide.

I would recommend doing the Synergy track bar and Synergy track bar brace. If you do not do the Ram Assist, add to that the Synergy sector shaft brace. Or don't... you decide on the corners to cut and reliability reduction to accept.

Your wallet, your decisions.

That is a good start.


This is helpful! Thanks!
 

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37's will fit with a 2.5 lift, and flat fenders. Not sure how it will do fully flexed out though. I will find out during the next off-roading event.

I would strengthen the d30 if you want to run it. At least gusset it. These tires are pretty damn heavy. 3.73 gears would not be fun at all to drive on. 5:13's go in next week for me, so I should see a huge improvement from where I am




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^^^^^
Gussets are not nearly as important as a truss... be it a factory D30 or a factory 44. Both suffer the same drawback of the tubes bending. The stock C will typically out last the stock tube in a battle.
 

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I did the following

Complete Lift (all8 control arms, etc)
F&R track bars
Tires
Wheels
Tie Rod
Drag link
PSC XD Steering box
Truss F&R
Gussets
Axle shafts
Gears 5.13 & diff covers
Bigger Front rotors - 37's greatly decrease OEM stopping ability

and there is still more to do ....
 

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I did the following

Complete Lift (all8 control arms, etc)
F&R track bars
Tires
Wheels
Tie Rod
Drag link
PSC XD Steering box
Truss F&R
Gussets
Axle shafts
Gears 5.13 & diff covers
Bigger Front rotors - 37's greatly decrease OEM stopping ability

and there is still more to do ....
that is a nice list of things. My parts are going on this weekend:

D44 front (gusset/Sleeved) 5:13 gears (stock Locker)
D44 Rear (gusset/Sleeved) 5:13 gears (stock Locker)
NR 4X4 Grade 8 bolts
1/2 spacer for front springs (get rid of the rake)
PS D44 cover (front already has upgraded dif cover)
PowerStop Z23 Front and Rear rotors/pads
JKS adjustable Front trackbar
RPMFAB Aluminum tie rod (already have the synergy drag link)

Gonna be a busy weekend for me lol
 
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