Lets talk about running 40s

[OBJLU]

I've been in the same position thinking about running 40's down the road. My original plan was 2.5" lift and 35's, bumpers, sliders, etc... Every day I see my Jeep on 2.5" of lift and 35's, I can't help think to myself "it looks so small". I've wheeled in 5 different states knocking out some badge trails and I just want to keep going bigger. The past few years my motto has been "buy once, cry once" and that's the approach i'm taking with the rest of my build.

My JLU is a 2018 Sport S with a 2.5" Clayton Offroad Overland Plus lift and 35" tires. I've really enjoyed my Clayton lift but I don't think swapping for their 3.5" springs will fit the bill. I think swapping to a 4.5" kit is going to be the best option, though I'm not sure which kit yet.

Obviously the stock M186 front axle won't suffice and the M220 LSD i picked up at a great price, won't be staying on the vehicle either. I considered finding D44 take off's and putting money into beefing them up but I don't get the piece of mind like I would with 60's. Buy once, cry once, right? The Fusion Elite Kingpin 60 front axle and Elite 60 Full Float rear axle combo should handle anything it's up against. 5.13 gears, Eaton E-lockers, RCV's, chromoly shafts, everything.

https://www.fusion4x4.com/online-st...ite-Full-Float-60-Jeep-Wrangler-JL-p111778164

Custom drive shafts will go in. Remaining steering will be beefed up. Stock fenders will get replaced with some sort of flat fender. And a new set of beadlocks will compliment the 40's. It'll be a minute before all this happens because there's $20K parts from the axle and lift alone. The Jeep is getting paid off early in 2021 and once that's done, it's game on.

I beefed up my axles but will swap em once fusion 4x4 decides to release a semi float hybrid like they did for the JK. Same tubes and ring and pinion as the 60 axle but 44 outers. Since I'm not doing any crazy rock bouncing and high HP I should be in grei shape with that combo.

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[JMoore]

How's the tire rub on the frame with 40's when turning with stock width axles? Are people having to run spacers or able to manage it with getting the proper wheels?

 

[jlroman2]

Interesting thread you guys have here. I just secured two rubicon axles for my Sahara. Down the road I’m planning to run 5:13 gears, upgrade axle shafts, and truss both. 40s are definitely tempting. These 44s are HEAVY! So of course you right away think they can handle them. I’m running 35s for now but I may upgrade to 38s before or during Jeep Beach. But I mean 38s? Might as well go 40s.... or so you tell youraelf.

 

[Kreepin1]

Interesting thread you guys have here. I just secured two rubicon axles for my Sahara. Down the road I’m planning to run 5:13 gears, upgrade axle shafts, and truss both. 40s are definitely tempting. These 44s are HEAVY! So of course you right away think they can handle them. I’m running 35s for now but I may upgrade to 38s before or during Jeep Beach. But I mean 38s? Might as well go 40s.... or so you tell youraelf.

If you have an easy right foot and will stick to easier trails you'll be fine. If you want to run trails and attempt obstacles that require 40's then you need to rethink your plan, 60's with 5.38's or better.

I ran 40's on my CJ-7 with a Dana 44 front for years, 4.88 gears, CTM u-joints, Warn and Superior shafts... After the 3rd time something broke I bit the bullet and replaced it with a 60.

RCV rates their 44 shafts for 40's but the ring and pinion is on you. Larger tires create a double whammy on the ring and pinion. Not only is more torque transferred from the larger diameter tire, but you need lower gears to compensate. If you look up a chart of gear sets you find the number of pinion teeth get fewer and fewer with lower gears. What is actually happening is that the ring gear diameter is fixed. Lower gears have smaller diameter pinion gears. This means that a Dana 44 with 3.45's and a doubler in the transfer case would survive better than one with 5.13's. Yes, it would suck on the road, but be stronger on the trail.

 

[OBJLU]

I'm sticking to my 39 BFG KM3s, they are a tad taller than the milestar 38's and a better tire. They weigh 87 lbs, not the lightest tire but with my RCV,s/Cromoly shafts, trusses and ball joints I think my axles will last, that said I know a couple of guys in my area that are running King of Hammers trails a couple times a month on 40's and the Dana 44's and nothing has broken yet. One of them is still on his stock rear shafts.

 

[jlroman2]

I'm sticking to my 39 BFG KM3s, they are a tad taller than the milestar 38's and a better tire. They weigh 87 lbs, not the lightest tire but with my RCV,s/Cromoly shafts, trusses and ball joints I think my axles will last, that said I know a couple of guys in my area that are running King of Hammers trails a couple times a month on 40's and the Dana 44's and nothing has broken yet. One of them is still on his stock rear shafts.

How you liking the KM3s? I’m considering them. Tbh the KM3 39s weigh like 1lb more than 37” Nittos. Considering doing the upgrade since a lot of people run 37s on stock rubi axles.

 

[OBJLU]

How you liking the KM3s? I’m considering them. Tbh the KM3 39s weigh like 1lb more than 37” Nittos. Considering doing the upgrade since a lot of people run 37s on stock rubi axles.

I like them I ran a couple trails out in Johnson valley and they killed it.

 

[OBJLU]

How you liking the KM3s? I’m considering them. Tbh the KM3 39s weigh like 1lb more than 37” Nittos. Considering doing the upgrade since a lot of people run 37s on stock rubi axles.

I got to park next to a jeep running the milestar 38’s and the km3 39’s are noticeably bigger

 

[jlroman2]

I got to park next to a jeep running the milestar 38’s and the km3 39’s are noticeably bigger

Yes my buddy just got them and you can tell right away.

 

[jlroman2]

38a Patagonia’s and 39s KM3s

 

[69 ORIGINAL]

Just stumbled on this thred. Sounds like some pretty high marks for the Patagonias. My local shop owner runs the 40's and loves them. With the relatively low price and anecdotally high marks, are there any downsides?

 

[J0E]

I wound up going with the KM3 39's, I think they're a good compromise at 87 lbs and 37.5 inches mounted. With all the traction out here and way I wheel my setup will last long enough for me to put some semifloat 60's on it. I am not going full float, I don't jump my Jeep and I wheel slow.

I agree, that's the maximum R (Radius) with your setup and *I don't jump my Jeep and I wheel slow.*

Too much Torque (T) breaks the drivetrain at the weakest point. T=RXF so your radius is 38.5/2
R drops if you air down, see my site bt39.com (BigTires39inches).

But 87 lbs is insignificant in *I don't jump my Jeep and I wheel slow.* but does apply to King of Hammers wheeling.

Your KTM is 13.6" wide. I'll going a bit more conservative with 38X15.50R18LT open country M/T which are 37.7" tall but 15.9" Wide. I'm really tempted to go with KTMs for .4" more height but giving up 2.3" width. The 15.9" width is probably going to cause rubbing problems.

 

[OBJLU]

I agree, that's the maximum R (Radius) with your setup and *I don't jump my Jeep and I wheel slow.*

Too much Torque (T) breaks the drivetrain at the weakest point. T=RXF so your radius is 38.5/2
R drops if you air down, see my site bt39.com (BigTires39inches).

But 87 lbs is insignificant in *I don't jump my Jeep and I wheel slow.* but does apply to King of Hammers wheeling.

Your KTM is 13.6" wide. I'll going a bit more conservative with 38X15.50R18LT open country M/T which are 37.7" tall but 15.9" Wide. I'm really tempted to go with KTMs for .4" more height but giving up 2.3" width. The 15.9" width is probably going to cause rubbing problems.

All good points and awesome website, I’m a min/maxer so always interested in the data!

 

[av8or]

"I would rather flip this bitch upside down and light it on fire than turn around."

Man have I felt like that before!

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