Another 37 vs 40 thread

SLO

SLO

Member
I know...there are about 800 of these posts out there. Trust me, I have read at least 750 of them over the last month. But, most of the opinions are based on a person with D30's or factory 44's looking to go to 40's and most of the advice against 40's has to do with the additional cost and weight relative to the 3.8 or 3.6. My situation is a little different. I have a 2013 Rubicon that is down at Motech right now getting a LS3 swap as well as Dana 60's from Fusion 4x4 (including Adams 1350's). I still need to buy new wheels and I am on the waitlist with Trail Ready (which is 4 months right now as they switch facilities). I am currently running 37's with a 3.5" Game Changer lift and Metalcloak Overland fenders. With Fusion 4x4 building my axles, I can specify any length. All that said, do I stay with 37's or sell the tires and wheels together and go up to 40's? I will have the power and axle strength regardless but do I enjoy the lower unsprung weight of the 37's and endless power of the LS3 without having to worry about cutting sheetmetal? Or, is it stupid to be 90% of the way to be able to run 40's and not run 40's? Most of the guys that wheel a lot seem to think that 40's don't really enable you to go to places that 37's cant. Last points I'll make is that this is not a daily driver and I live in Oregon so most of the trails I do are at Browns Camp plus an annual trip to Rubicon and Moab.
 
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J

JKDream

Guest
SLO said:
I know...there are about 800 of these posts out there. Trust me, I have read at least 750 of them over the last month. But, most of the opinions are based on a person with D30's or factory 44's looking to go to 40's and most of the advice against 40's has to do with the additional cost and weight relative to the 3.8 or 3.6. My situation is a little different. I have a 2013 Rubicon that is down at Motech right now getting a LS3 swap as well as Dana 60's from Fusion 4x4 (including Adams 1350's). I still need to buy new wheels and I am on the waitlist with Trail Ready (which is 4 months right now as they switch facilities). I am currently running 37's with a 3.5" Game Changer lift and Metalcloak Overland fenders. With Fusion 4x4 building my axles, I can specify any length. All that said, do I stay with 37's or sell the tires and wheels together and go up to 40's? I will have the power and axle strength regardless but do I enjoy the lower unsprung weight of the 37's and endless power of the LS3 without having to worry about cutting sheetmetal? Or, is it stupid to be 90% of the way to be able to run 40's and not run 40's?
Click to expand...

I'd run the 40's personally.
I want to run them right now, and I could swing the axles - but the 3.6 doesn't cut it on 37s for me already, so 40s wouldn't work without a motor upgrade - and that puts it out of budget. Given that you already have axles, and a solid powerplant, I'd definitely bump up the tire size.
I'd ask yourself though - are you already using the 37s to their limit? Rolling over every obstacle with ease isn't fun - or at least to me it isn't.
 
wjtstudios

wjtstudios

Hooked
Great choice on Fusion. Dan was great to work with. I had mine built with 68.5” width. I’m running 37s with 4:88s as a daily driver. But I’m sure once it’s not, I’ll move it up to 39s or 40s and go 5:38s. I’m kind of liking the KM3 39s.

If I was your in shoes and the path you are already is 90% to 40s, I think you’ll regret 37s. Sounds like an awesome build!


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Mybadjk

Mybadjk

Caught the Bug
I’d say if you’re doing an ls swap, I’d definitely go 40s. I’m currently running 37s with my dynatracs. I’ll eventually switch to 40s


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SLO

SLO

Member
Thanks for the input. I’m surprised there isn’t a camp that have gone to 40’s and wish they would have stayed on 37’s.
 
SLO

SLO

Member
wjtstudios said:
Great choice on Fusion. Dan was great to work with. I had mine built with 68.5” width. I’m running 37s with 4:88s as a daily driver. But I’m sure once it’s not, I’ll move it up to 39s or 40s and go 5:38s. I’m kind of liking the KM3 39s.

If I was your in shoes and the path you are already is 90% to 40s, I think you’ll regret 37s. Sounds like an awesome build!


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Click to expand...

What backspacing are you running? Any suggestions on the Fusion axles? Things you would do different?
 
zimm

zimm

Caught the Bug
I'd go 40's if I were you. You already got the axles, HP, and the 8 lug wheels- why not?
 
wjtstudios

wjtstudios

Hooked
SLO said:
What backspacing are you running? Any suggestions on the Fusion axles? Things you would do different?
Click to expand...

4.63” back spacing on 68.5” axles with 37x12.5” BFG KM2s. I have plenty of clearance on the frame for turning and my wheels are about 3” proud of the stock flares. With the 72” axles you will be around 4.75” past the edge of the flare depending on your back spacing. My set is the 60/44 hybrid front and SF 60 rear.

Image1539380856.673089.jpg

Make sure to ask Dan to have both the front and rear tubes welded to the diff housing. I had him provide the 2.5 ton tie and drag link. Make sure it has the ram assist tab welded to the axle and that you order the ram mount for the tie rod.

The only thing that I would have done differently is order the 60/60FF or the 60/80FF but at the time I built that stage it was my daily driver and on 37s. My circumstances have now changed and it’s going to move to a toy/ trail rig and I’m sure I’ll be talking to dan in the near future.

If your not in production yet, you could consider bumping up to the 80 and be done permanently.

Other things you need to added to your list is ram assist, probably PSC. And a Larger brake booster for the 60s.

Hope this helps! Good luck with the build.


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13_gecko_rubi

13_gecko_rubi

Caught the Bug
Dan is a great guy!!! If you go 72 you will want deep BS. I'm running 4.75 bs on my prorocks because I didn't want the hub sticking past wheel. It's about 88.5 wide with the 72.5 axles and 40s. Gets tight in the woods but very stable off camber.

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SLO

SLO

Member
wjtstudios said:
4.63” back spacing on 68.5” axles with 37x12.5” BFG KM2s. I have plenty of clearance on the frame for turning and my wheels are about 3” proud of the stock flares. With the 72” axles you will be around 4.75” past the edge of the flare depending on your back spacing. My set is the 60/44 hybrid front and SF 60 rear.

View attachment 312489

Make sure to ask Dan to have both the front and rear tubes welded to the diff housing. I had him provide the 2.5 ton tie and drag link. Make sure it has the ram assist tab welded to the axle and that you order the ram mount for the tie rod.

The only thing that I would have done differently is order the 60/60FF or the 60/80FF but at the time I built that stage it was my daily driver and on 37s. My circumstances have now changed and it’s going to move to a toy/ trail rig and I’m sure I’ll be talking to dan in the near future.

If your not in production yet, you could consider bumping up to the 80 and be done permanently.

Other things you need to added to your list is ram assist, probably PSC. And a Larger brake booster for the 60s.

Hope this helps! Good luck with the build.


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Click to expand...

Thanks for the recommendations.

Aren't the tubes always welded to the diff housing?

I am going 60/60FF and Motech will be doing the PSC hydro assist at the same time as the LS swap so Dan will be welding the tab for the assist when he builds the axles. I was thinking I would go 70" wide and ordering the Trail Ready HD17's in a 5" backspace but I do like the idea of a readily available wheel that is 4.75". Methods aren't my favorite but they do come in a 4.75 backspace which I like. Otherwise, it would be XD's or the like.

I already have the Mopar big brake kit so I will retain the larger booster and master cylinder.

Sounds like the only decision is a rear 80...
 
SLO

SLO

Member
13_gecko_rubi said:
Dan is a great guy!!! If you go 72 you will want deep BS. I'm running 4.75 bs on my prorocks because I didn't want the hub sticking past wheel. It's about 88.5 wide with the 72.5 axles and 40s. Gets tight in the woods but very stable off camber.

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Click to expand...

At what backspacing will the hub stick out past the wheel? Or does it depend on the hubs? I was thinking 70" with 4.75" to 5".
 
wjtstudios

wjtstudios

Hooked
SLO said:
Thanks for the recommendations.

Aren't the tubes always welded to the diff housing?

I am going 60/60FF and Motech will be doing the PSC hydro assist at the same time as the LS swap so Dan will be welding the tab for the assist when he builds the axles. I was thinking I would go 70" wide and ordering the Trail Ready HD17's in a 5" backspace but I do like the idea of a readily available wheel that is 4.75". Methods aren't my favorite but they do come in a 4.75 backspace which I like. Otherwise, it would be XD's or the like.

I already have the Mopar big brake kit so I will retain the larger booster and master cylinder.

Sounds like the only decision is a rear 80...
Click to expand...

I know they’ll perimeter weld them together. I don’t think all axles are more than the plug welds. The perimeter weld takes it to another level.

Image1539391195.970449.jpg

Verses this on my CJ

Image1539391241.990768.jpg

Sounds like you have most of it worked thru.


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13_gecko_rubi

13_gecko_rubi

Caught the Bug
SLO said:
I’m assuming the huge difference is a good thing? Did 40’s take away any of the fun?
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Who do you usually wheel with? What is their setup? Where do you usually wheel? Those are big questions to answer yours. I run 40s and love it when traveling out of state with all my friends that are running 42s. When I'm in Michigan with my other buddies on 35/37s it is pretty boring. I got a set of 37s just to run here to make it more fun. Not sure I'll like the 80 rear with 37s (crappy ground clearance) but we'll see lol. I mean there are places in Michigan I can use the 40s it's just highly limited.

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Irish JK

Irish JK

Caught the Bug
13_gecko_rubi said:
Who do you usually wheel with? What is their setup? Where do you usually wheel? Those are big questions to answer yours. I run 40s and love it when traveling out of state with all my friends that are running 42s. When I'm in Michigan with my other buddies on 35/37s it is pretty boring. I got a set of 37s just to run here to make it more fun. Not sure I'll like the 80 rear with 37s (crappy ground clearance) but we'll see lol. I mean there are places in Michigan I can use the 40s it's just highly limited.

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Click to expand...

80 with 37s blew. It was like dragging a shovel around.


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