Performance 40s vs 37s

[Basscat]

Which coilovers are you looking at?

I was looking at EVO Double Down Pro which obviously includes the long arms. Was looking at running that with XD60/PR 80 and 40s. Had several folks on here say that setup wasn't built for 40s. You may have been one of them come to think of it? When I called EVO I spoke with Mel and Andrew. Both of them said for what I was thinking of doing (Colorado type wheeling and no real desert bombing) the DDP was the ticket and their setup (250/250f, 200/250r) was pretty close to right. That said I also read the coilover thread started by wayoflife and many think the EVO coilovers as they're set up are a bit soft and saggy in the rear? Open to input!


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[Lil Nasty]

For arguments sake, the Curries seem to have done fairly well with 4" coils and shocks on 37s, 39s/40s

And for discussion sake, how would a coilover provide more travel if the shock had the same stroke length?

More adjustability, yes...coilover wins

I would think you'd be fine on your plush ride coils, make sure you have trimmed where necessary and have your bump stops set correctly

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Just to further elaborate. The mounting points of the coil-over are different than the points for a shock. This prevents a shock from getting the same amount of travel. The cantilever setup of evo is engineering at its finest to allow so much travel with the limited room provided. Even the bolt on kit raises the front mount higher. Attempting the same with shocks would make the coils the weak link in the system.


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[TrainWreck618]

I was looking at EVO Double Down Pro which obviously includes the long arms. Was looking at running that with XD60/PR 80 and 40s. Had several folks on here say that setup wasn't built for 40s. You may have been one of them come to think of it? When I called EVO I spoke with Mel and Andrew. Both of them said for what I was thinking of doing (Colorado type wheeling and no real desert bombing) the DDP was the ticket and their setup (250/250f, 200/250r) was pretty close to right. That said I also read the coilover thread started by wayoflife and many think the EVO coilovers as they're set up are a bit soft and saggy in the rear? Open to input!


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Seems like a solid plan besides the suspension. Your going to have big horsepower, big axles, big tires, and little suspension. Im sure it will work, but 37's on that setup will give you more travel. Evo's bolt on coilovers were not designed for 40" tires

 

[Basscat]

Seems like a solid plan besides the suspension. Your going to have big horsepower, big axles, big tires, and little suspension. Im sure it will work, but 37's on that setup will give you more travel. Evo's bolt on coilovers were not designed for 40" tires

So given I won't be bombing through the desert but rather typical Colorado / Moab wheeling might I be better served opting for a good 3" or 4" spring and a really good 2.5 internal bypass adjustable shock? Or ? What? Appreciate the input by the way.


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[TrainWreck618]

So given I won't be bombing through the desert but rather typical Colorado / Moab wheeling might I be better served opting for a good 3" or 4" spring and a really good 2.5 internal bypass adjustable shock? Or ? What? Appreciate the input by the way.


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This is a tough question. I was faced with the same questions a few months back and ultimately decided that I would just stay on 37's until I could upgrade to the DTD. I also have heard of others having issues with an LS and bolt-on coilovers. Something about putting it in gear and raising up to high? idk..

 

[jkLogan]

So. Much. Wonderful. Knowledge. This place is great!

 

[Basscat]

Well. I know we're straying from my original question which was "what is the performance / capability difference between 37s and 40s?" I know there aren't many on here running 40s but what little I hear doesn't scream " 40s crap all over 37s". Very much appreciate the insight on coilovers and big axles with 40s Trainreck! Maybe 37s is the perfect all purpose size? Don't need a PR80 rear with 37s IMO; even with the LS. An XD60 full float would work just fine. Perhaps that opens up more suspension options as well?


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[tgoss]

Agreed, trainwreck, thank you for the insight.

 

[rockwell]

That's a tough call. If 37s are the objective you don't necessarily need the pro rock package but you do need a PR 44 front to do it right IMO. The rear axle tube on the JKU is pretty beefy and new 4130s in a 32 spline (semi float) will certainly work, again just my opinion. The V8 is a game changer and with the right transmission (think 6L80/90) the old school thinking of chasing deep gears to compensate simply goes away

A front prorock 44 is a no brainer for me. I realize the rear axle is already pretty decent, but I'd want to go with an ARB and 35 spline shafts and regear. By the time I do that, and sell the rubicon rear, for the price difference I get a prorock 60 for more strength and high pinion to keep my driveshaft out of the rocks.

 

[Basscat]

A front prorock 44 is a no brainer for me. I realize the rear axle is already pretty decent, but I'd want to go with an ARB and 35 spline shafts and regear. By the time I do that, and sell the rubicon rear, for the price difference I get a prorock 60 for more strength and high pinion to keep my driveshaft out of the rocks.

True. But don't expect much of anything for your rear when you sell it. Given you were contemplating the axle set and a V8 I was thinking along the lines of minimum needed underneath which gets you to the V8 swap sooner.


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[Ddays]

A front prorock 44 is a no brainer for me. I realize the rear axle is already pretty decent, but I'd want to go with an ARB and 35 spline shafts and regear. By the time I do that, and sell the rubicon rear, for the price difference I get a prorock 60 for more strength and high pinion to keep my driveshaft out of the rocks.

If you do go with the PR rear I would strongly suggest you go with a Full Float option in lieu of the Semi Float. IMHO with the newly revised Dynatrac price structure the difference isn't worth it. At minimum, if you do go with the SF, I'd suggest you buy a spare axle for peace of mind...

 

[wayoflife]

What are the trade offs going from 37" to 40"?

The biggest trade off going to 40's is that you WILL start breaking shit IF you actually play as hard as you think you do.

Doing 40s right (IMO) means full width axles and changes in back spacing along with other mods. Does the wider track width have down sides or is the extra 3" to 4" not noticeable?

Doing 40's "right" is relative to how hard you actually push your Jeep. As mentioned, a wider track will allow you to lower your COG but a wider width can be a liability on some trails. This is the biggest reason why I've worked on slimming my JK's down. That being said, the biggest reason to upgrade your axles is for STRENGTH - PERIOD.

I realize the extra unstrung weight and rolling mass are likely horsepower sapping but how much on a V8? Just barely noticeable and 5.13 to 5.38 fixes it or so much that horsepower mods are needed?

"Needed"? Far from it. You drive a Jeep, not a Corvette - it's a brick in the wind and that it can reach highway speeds at all is a wonder in itself. Is more HP "nice to have"? Well duh! :crazyeyes:
In spite of what some will suggest, I ran Moby on 40's for years with just a 3.8L and people still bitched at me for driving too fast.

Coilovers would likely allow one to keep the same ride height (4") they had with springs and shocks on 37s? Yes? No?

You should be able to keep whatever ride height like 4" you want with or without coil overs. Ride height is NOT why you'd want coil overs.

Has anyone on here gone to 40s, not liked it and gone back to 37s? If so, why?

As mentioned, I've run 40's and gone back down to 37's but not because I didn't like it but rather, it was stupid of me to do and use my Jeep the way I do being that I only have a ProRock 44 up front. I only ran that setup to test the Dynatrac Progrip brakes. Based on past experience running 40's on a 44 in the past, I know it wouldn't take long for me to break something.

Finally, what's the performance / capability advantage of stepping up to 40s? I've wheeled on 37s and 60s front and rear with the old TJ and loved the unsparing weight. It was like the TJ was stuck to the rocks. JKUs are much bigger so my thinking is 40s are to a JKU what 37s were to a TJ.

I've run a TJ with 37's and can tell you, the TJ is no JK and far from being a JKU on 40's. If you have to ask what the "performance gains" are, you don't play on the kind of trails or obstacles that would make them nice to have. This is NOT a put down but rather, a reality check based on my opinion.

2) differences in on road driving manners are

Note: mine is not a daily driver but I don't want a borderline trailer queen either.

In my opinion, you ain't building a Jeep up right if you didn't consider it to be just as comfortable or handle as well as a daily driver.

 

[wayoflife]

For arguments sake, the Curries seem to have done fairly well with 4" coils and shocks on 37s, 39s/40s

Just because professional drivers have "done fairly well" with 4" coils and shocks doesn't mean that you couldn't do it better. Just because they're willing to suffer through a miserable ride to compete in a race doesn't mean that you should have to too especially if you're just going wheeling with your buddies.

And for discussion sake, how would a coilover provide more travel if the shock had the same stroke length?

If the kit is designed correctly, the upper coil over mounts are relocated to a much higher position over your factory shock mounts or uses a system that completely works around it like the way an EVO lever system does. This not only allows you to have a greater amount of stuff, it'll allow you to run at a lower ride height AND allow you to run a longer shock that'll provide significantly greater travel.

More adjustability, yes...coilover wins

There's a lot more that coil overs provide than just adjustability. If the mounts are designed correctly, they will offer significantly greater travel and allow you to run 2 coils of different spring rates of your choice separated by a timing ring.

 

[Robertcrav]

Just because professional drivers have "done fairly well" with 4" coils and shocks doesn't mean that you couldn't do it better. Just because they're willing to suffer through a miserable ride to compete in a race doesn't mean that you should have to too especially if you're just going wheeling with your buddies.



If the kit is designed correctly, the upper coil over mounts are relocated to a much higher position over your factory shock mounts or uses a system that completely works around it like the way an EVO lever system does. This not only allows you to have a greater amount of stuff, it'll allow you to run at a lower ride height AND allow you to run a longer shock that'll provide significantly greater travel.



There's a lot more that coil overs provide than just adjustability. If the mounts are designed correctly, they will offer significantly greater travel and allow you to run 2 coils of different spring rates of your choice separated by a timing ring.

Understood, and I should have clarified that if the shock and Coil-over were the same length mounted in the same way...

The evo-lever really intrigues me for all of those benefits as well...just a matter of $$ [emoji16]





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[Basscat]

The biggest trade off going to 40's is that you WILL start breaking shit IF you actually play as hard as you think you do.



Doing 40's "right" is relative to how hard you actually push your Jeep. As mentioned, a wider track will allow you to lower your COG but a wider width can be a liability on some trails. This is the biggest reason why I've worked on slimming my JK's down. That being said, the biggest reason to upgrade your axles is for STRENGTH - PERIOD.



"Needed"? Far from it. You drive a Jeep, not a Corvette - it's a brick in the wind and that it can reach highway speeds at all is a wonder in itself. Is more HP "nice to have"? Well duh! :crazyeyes:
In spite of what some will suggest, I ran Moby on 40's for years with just a 3.8L and people still bitched at me for driving too fast.



You should be able to keep whatever ride height like 4" you want with or without coil overs. Ride height is NOT why you'd want coil overs.



As mentioned, I've run 40's and gone back down to 37's but not because I didn't like it but rather, it was stupid of me to do and use my Jeep the way I do being that I only have a ProRock 44 up front. I only ran that setup to test the Dynatrac Progrip brakes. Based on past experience running 40's on a 44 in the past, I know it wouldn't take long for me to break something.



I've run a TJ with 37's and can tell you, the TJ is no JK and far from being a JKU on 40's. If you have to ask what the "performance gains" are, you don't play on the kind of trails or obstacles that would make them nice to have. This is NOT a put down but rather, a reality check based on my opinion.



In my opinion, you ain't building a Jeep up right if you didn't consider it to be just as comfortable or handle as well as a daily driver.

Appreciate the input


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[13_gecko_rubi]

One other thing to consider is where do you normally wheel and who do you normally wheel with. I stepped up from 37s to 40s and yes there is obviously a benefit there. The thing I most dislike about it is around here (Michigan) the 40s render most of our trails a walk in the park now. My group of wheeling buddies typically heads south or west a few times a year where I can actually put them to use. I was (and still am) the smallest Jeep in the group, I was more than happy on my 37s and the Jeep went pretty much all the places I wanted it to. But over the years I started trying harder and harder trails and eventually got to the point that the 37s weren't cutting it. Then I stepped it up to 40s. Unless you really need them you will spend a lot of money to make your Jeep more capable than you may need. It's great to only spend the money once but it's also nice to build it up as your wheeling style changes. If you use quality parts you can always sell them for a decent amount when you upgrade.

And as for on road, I totally agree with Eddie. You want to make sure your on road performance is just as good as offroad. 95% of the miles i put on my jeep are driving to work so not going to deal with crappy ride just to have a great trail rig a handful of times per year



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[still in school]

This is a tough question. I was faced with the same questions a few months back and ultimately decided that I would just stay on 37's until I could upgrade to the DTD. I also have heard of others having issues with an LS and bolt-on coilovers. Something about putting it in gear and raising up to high? idk..

Crap, I just ordered bolt-on coilovers last month.

 

[TrainWreck618]

Crap, I just ordered bolt-on coilovers last month.

Why crap? Bolt on's are pretty sweet

 

[Basscat]

I'll play because I'm right there with you.

I agree with you, if you want to run 40's and do so comfortably IMO you need to run full width, full float axles. The extra width will help in many ways, keeping the cog low is key and keeping those tires out of the body. Full floating axles to keep that weight on the axle tubes and not just the flanges is just as important as well unless you don't mind swiping out unit bearings constantly and love trail breakdowns and repairs.

Reliability is the one thing I stress when building any of my vehicles, and I want them to be multi-purpose. I want to drive it to the trail/track and beat on it, then I want to drive it home. Then when home I want to get groceries or go to dinner or commute to work in the same vehicle. If that wasn't the case I would just build a stripped race car or a buggy in this case.

Performance.... This is just a word I've completely forgotten about with my Jeep. I have 37's now, 5.13's on a PR44/60 combo and while on the trail and in the rocks I cannot complain about anything. The minute I leave the trail and get on the freeway to head home I really start despising the Jeep.

So with you, I wonder if I need to change over to coilovers too if I went with 40's on full width axles or can I keep the 4" plush rides. I hope someone can help me with that because I love how the Jeep rides now, and really don't want to change it up.

This is a good question tgoss asks! If you were running 40s (regular trail riding; not high speed bombing) would you opt for 4" plush rides and 2.5s or the bolt on coil over kit?


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[wayoflife]

This is a good question tgoss asks! If you were running 40s (regular trail riding; not high speed bombing) would you opt for 4" plush rides and 2.5s or the bolt on coil over kit?

I'd still go with the bolt on coil overs if only because they would offer more flex.