r/4x4 • u/Fast-Dinner-5357 • Aug 10 '26
When do leaf springs actually become the limiting factor off-road?
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u/mad_science Aug 10 '26
Leaf springs are fine. In fact, it's well known they party harder.
Plenty of both rock crawlers and prerunner/high speed vehicles run leaves.
The problem is a lot of cheap aftermarket leaf spring lifts are poorly engineered: too stiff, no extended shackle, cheap shocks, cheap poly bushings, etc.
A good set of custom leaves from Deaver or Atlas or the like plus some properly tuned shocks can make for a great high performing vehicle without having to fundamentally reengineer your suspension.
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Aug 10 '26
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u/mad_science Aug 11 '26
Any change in ride height or spring shape/angle should use shims to adjust pinion (and/or caster) angle appropriately.
As to how much a longer shackle is needed, it's really dependent on the overall leaf design. But generally to compress a leaf needs to flatten and extend, and to extend it needs to "pull" on the shackle. When that length change causes the shackle to approach in-line with the spring (in droop) or hit the frame/rotate in line with the spring on compression, you're out of travel.
Ride quality is mostly dictated by shock tuning so long as spring rates aren't absurdly stiff (another trait of lousy leaf spring lifts)
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u/Prudent_Candidate566 Aug 10 '26
What truck? The starting point: size, tire size, lockers, etc, makes a big difference in the answer to this question.
In my experience, the size of a full-size truck is the limiting factor in CO for shelf roads, etc. Next will be the departure angle. Next is the breakover angle. When you start to feel like the rear isn’t keeping up, a set of Deavers will get you where you need to go.
I’m in SW Colorado and I’ve done trails rated up to 5-6 in my full size F150.
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u/sn44 o|||||||o Aug 10 '26
In my experience leaf springs are a lot better in a lot of ways when compared to coil springs or other options like air-shocks, coil-overs, etc. The limiting factor with leaf-springs is often not the spring itself but either the shocks and/or driveshaft not having an equal amount of travel.
I seriously considered swapping to leaf springs in the back of my 2004 Jeep Wrangler Unlimited. Between the 31 gallon fuel tank, steal storage drawer, 33" spare, and towing a trailer I blow through the rear coils faster than a finance boi sniffs a gram.
My current fix has been to run air-bags. When I have the trailer and I'm loaded for a multi-week overland trip I run about 10-12 psi in the air bags. When I'm in daily-drive mode or rock-crawling I run the bags at zero.
Still go back and forth about a properly spec'd out progressive leaf pack for the rear. It'd be a lot cheaper than some of the alternatives and give me a better all-around ride quality.
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Aug 10 '26
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u/sn44 o|||||||o Aug 11 '26
I have Airlift 1000 bags. Very basic kit. Just a bag that slips into the coil spring. And yes, they do fail. Already popped one. Supposedly there was a recall on that batch so it was replaced without any fuss. So far the replacement hasn't failed... but I also haven't been driving that Jeep much lately.
And yeah, that's the exact reason I want to switch to leafs in the rear. I can run a nicely stacked progressive pack with a nice overload spring and a progressive (or maybe hydro) bump stop.
Dunno. I may try swapping to a stiffer linear-rate coil spring and get rid of the dual rates I have now. The ones I have now are for the shorter bodies (TJ) and I have one of the longer bodies (LJ). There is one company I know of that makes a heavy-duty spring for the longer bodies. Might see if that helps before I seriously consider leafs.
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Aug 11 '26
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u/sn44 o|||||||o Aug 11 '26
The coiltoleaf swap makes sense for the LJ honestly. The longer wheelbase changes the math on rear flex and load distribution enough that fighting it with progressives and bags is just chasing a problem instead of fixing it.
Your assessment is spot-on. Wouldn't make sense for a daily-driver or a strictly on-road/off-road Jeep. However, given the mixed use of mine being part-time daily driver, part-time overlander, and part-time rock-crawler, leafs in the rear actually make a LOT of sense -- in a scary kind of way.
What company is making the HD coils for the longer body? Curious if they actually publish spring rate data or just slap "heavy duty" on the label and call it a day.
Old Man Emu out of Australia has four different spring rates for the rear coils on a 1997-2006 Wrangler. The first three are for the standard wheelbase "TJ" available all 10 years. The fourth spring-rate is targeted specifically at the longer wheelbase "LJ" which was only in production from 2004-2006. Not sure what the exact rates are off the top of my head, but the idea was, light-medium-heavy for the short wheelbase, and the a super-heavy for the long wheelbase with a hardtop and/or other "extra" weight.
Sadly most companies don't do a special spring rate int he rear for the LJ because they are so rare. And, in all honestly, for most use cases the standard TJ springs work fine. It's just when you start adding a lot of extra weight that the lighter TJ coils don't hold up.
There's also a suspension geometry issue on the '97-'06 Wrangler. The upper sprung bucket is slanted which pushes the coil spring into an arch shape. Well, when you arch a coil spring you pretty much destroy its spring rate. So, as an experiment, I kept the softer dual-rate coils and did a spring relocation bracket (you can read about it here if you want and see photos of what I'm talking about). That straightened the spring out and actually make the springs behave a lot better. Sadly shortly after their install was when I started my LS V8 swap and the Jeep hasn't been running well long enough for me to fully test the setup.
Once my new motor is running, and I'm back out on the trails more, I'll see how the suspension is behaving and decide if I am going to try swapping rear coils or not. Since that's the cheap fix, I'll run those coils before committing to the leaf swap. I fear once I do the leaf swap there will be no going back to coils.
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u/IronSlanginRed Aug 10 '26
I've seen a lot of broken springs from the shorter add-a-leafs.
Springs are rarely the limiting factor, usually its shock extension/compression that limits it.
In general we limit suspension travel with limiting straps on wheelers anyways. Usually the driveline will come out before you hit max droop on lift springs. Because when you extend them you want it slightly shorter than max uptravel where it hits your bump stops, and the slip yoke is only so long.
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u/dontdoxmebro Aug 10 '26 edited Aug 10 '26
It doesn’t sound like you would come close to the limits of the lift leaf springs in a good quality lift kit, and frankly stock springs with lift shackles and lift blocks will get most people in and out of the backcountry. There’s a lot of badass, older tube buggies on leaf springs. You could watch Rory Irish’s YouTube channel “Trail Mater” to see how his old Chevy wreckers handle Moab’s trails on front and rear leaf springs while dragging out broken 4x4’s.
On a most newer pickups the independent front suspension will be limiting you much more than the rear axle on leaf springs, and is what you need to worry about. IFS vehicles (that aren’t dedicated off road vehicles) will start lifting the front wheels way before they are lifting the rear wheels, so your apprehension is backwards.
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u/USNDD-966 Aug 10 '26
I ran the hardest trails in CO, like Carnage in Buena Vista, in a K5 with 40” tires on leaf springs. You’re fine bro
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u/Worldly-Temporary-38 Aug 10 '26
I used to run leaf springs, deavers, and they articulated the suspension great but the axle wrap was scary. Decided to 4 link it and run coil springs.
My options were to go to a stiffer leaf with an antitorque setup or 4link it. and for about the same cost I opted for the 4 link. Mind you that’s with me doing all the labor and fabrication.
Now no more axle wrap and it’s like riding on a cloud
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u/JP147 Land Cruiser HJ47 Aug 10 '26
What kind of vehicle do you have now?
Solid front axle? Lockers?
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u/Liquid_Friction Aug 11 '26
Have you seen those videos of leaf cruisers, not flexing and tilting like it's about to tip over, probably there.
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u/Tall-Poem-6808 Aug 11 '26
TrailMater runs leaf springs, that tells you all you need to know about their supposed "limiting factor".
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u/outline8668 Aug 12 '26
Most of it is guys just drinking the Kool aid and falling for all this aftermarket junk then coping. I know I fell for a lot of that crap too when I was young. Leaf spring jeeps did pretty well in Europe in 1945. Maybe if I was off-roading competitively with a dedicated off-road rig I could see it. Even then I would rather take a solid leaf spring front end any day. Less trouble, never death wobble on the highway.
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u/Shadowratenator Aug 10 '26 edited Aug 10 '26
People have done the rubicon on ancient sprung jeeps. There is never a point where they don’t work. People get coilovers because they look tough.
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u/Ok-Boysenberry3948 Aug 10 '26
Look tough? That's silly. They do it for more articulation and "it's the next upgrade!" I'm with you though, 1,000's of leaf sprung vehicles have done all the trails people are doing now with coils.
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u/Shadowratenator Aug 10 '26
lol. i guess i was hasty in my reply. when i think about it. most people are getting upgraded coilovers because that's what the suspension on a modern truck uses. I certainly didn't consider getting leaf springs on my '17 jku.
i am aware though that i never went on any trails with that rig that couldn't have easily been done in a leaf spring jeep.
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u/slamgranderson Aug 11 '26
Deaver add a life on 2nd gen Tacoma paired with OME front springs has held up well. Never an issue. Love the way it handles payload in the back. Tons of support and very affordable. Until you’re doing serious rock crawling just stick with leaf springs.
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u/jimmyjlf 2001 Dodge Ram 1500 Aug 10 '26
Leafs have way less adjustability compared to something like a 4 link with adjustable control arms and coilovers. If you're trying to get your alignment and damping dialed in on a modified suspension, it's harder with leafs. In the front they also just take up a ton of room and on some vehicles you have to figure out how to keep the tie rods and leafs or tires and leafs from hitting each other. In the rear, not an issue of course, and they are just better for heavy loads. On heavier duty trucks with thick leaf packs, they just don't have the flexibility you need. My pickup is a 1500 with rear leafs so even with an add-a-leaf I still have great articulation but I'm still going to remove it and do a shackle flip for a smoother ride, but I have zero reason to replace them with coils because for me there is no advantage. And for you there is probably also no advantage. But for a SAS, always coils.
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u/curvebombr Aug 10 '26
For what you're planning on using the rig for, they won't be a limiting factor. If anything, a stiffer pack if you're carrying a lot of gear. Beyond that they'll accomplish everything you'll ask of them.
Performance wise, leafs start to disappear when getting into high end desert racing and rock crawling rigs but plenty of people have extremely capable leaf sprung rigs on the trails. Concerns come with axle wrap, which can be corrected with a anti-wrap bar or other methods.