What leaf spring rate?

ericsennert

NAXJA Member
NAXJA Member
Is there some kind of formula out there or way of figuring out what leaf spring rate you need? There's got to be a way to do it without just shooting from the hip, buying springs, throwing them in, calling it a day. My machine weighed 3900 lbs empty before I built the rear bumper/tire carrier. This weekend I'm going to put my front bumper/winch on and scale it again. Right now my rear springs are IRO 3.5 inch 7 leaf packs at 185 lbs. The optional 8th spring will take it to 215. Front coils are PAC 4 inch 250 lbs. I'd like this thing balanced as correct as possible. TIA
 

RCP Phx

New member
Not really, almost all the manufacture's have different spring rates and arches to achieve the same lift height.
 

Tim_MN

Freakish Hand Strength
NAXJA Member
Spring rate is more an indication of the "softness" or "firmness" of the springs than anything else. The rate you need is whatever achieves how you want the Jeep to feel. Having the spring rates "balanced" isn't very high on the things you should be considering. Do keep in mind the front/rear weight distribution is not equal either.

There are some spring rate threads in the NAXJA FAQ's and in archived threads.
 

ftwelder

New member
Leaf springs don't have linear rates of progression and variables like shackle length, angle, mounting surface and friction have a big effect on overall rate and progression curve. straight gauge coils are inch/inch rate of progression from bottom to top. Or so I hear.
 

ericsennert

NAXJA Member
NAXJA Member
Leaf springs don't have linear rates of progression and variables like shackle length, angle, mounting surface and friction have a big effect on overall rate and progression curve. straight gauge coils are inch/inch rate of progression from bottom to top. Or so I hear.
Ok. But I'm sure the spring weight needs to be increased as the vehicle weight is increased, right?
 

Tim_MN

Freakish Hand Strength
NAXJA Member
Interesting theory, wondering what supports this ? Are you exceeding the GVWR ? The gross vehicle weight rating (GVWR) is the maximum operating weight/mass of a vehicle as specified by the manufacturer including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers and cargo but excluding that of any trailers.

Extra weight will increase the static compression of the springs, and will likely increase the maximum compression as well, but spring compression is ultimately limited by the bump stops.

If you think it is necessary, you can buy springs with a greater load rating, but most people add coil spacers or slightly longer shackles/shackle relocation brackets if they feel the need to compensate for extra weight compressing the springs. My RE lift is fine with heavy duty front and rear bumpers, full skids, rock rails, spare parts, tools, and camping gear.

Did you find those spring rate threads ?
 
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RCP Phx

New member
Ok. But I'm sure the spring weight needs to be increased as the vehicle weight is increased, right?
In theory you are correct if nothing else were to change, but adding 200# bumpers to a 4000# vehicle is only a 5% change in weight. So a existing 200# spring would only go to 210#, see where I'm going here!
 

cal

NAXJA Warranty Voider
NAXJA Member
To argue that, most of our springs run around 200 inch pounds.

So adding 200 pounds to the rear of the car will drop it 1" (well, .5" as there are two rear springs).

I figure I load about 450 pounds of gear into my jeep. I dont want it dropping 2.25" of rear ride height when loaded - so knowing the spring rate helps me figure out what to do.

Do I go to a 450 pound spring?

Do I go to a 250 pound spring and lift the rear 2.25 (or maybe 1.12) over level to split the difference?


Actually all of that is wrong, since leaf springs are not a linear rate but are progressive, as you flatten out to engage each additional leaf more the rate increases, which is why higher end springs end up having 6, 7, 9, 11, etc leafs. Lets you be reasonable unloaded while not swamped under weight when loaded.

Easiest answer is just buy Deavers and forget about it. If you're going to be really heavy call them and ask them to thicken up the longest couple leafs for load.
 

sinat01

New member
I have the IRO leafs on mine with a rustys rear C&F bumper, The flop shop C&F panels and 2x6x1/4" rock rails and the iro springs didn't sag a bit. I also have a sub box with 2 12s in it so there is plenty of weight back there. even when I hook my trailer up it doesn't sag much at all and it still rides decent. Shocks are a big part of the ride. I had the doetsch tech twin tubes on mine and just swapped those out for their monotubes and it made a world of difference so you might wanna look at that too, but the IRO springs should be just fine
 

ericsennert

NAXJA Member
NAXJA Member
Today I put my front bumper and warn 8274 on and weighed it. Now it weighs 4460 with nothing in it and a full tank. According to the title this 98 SE was 3080 from the factory. "Shipping weight"
 
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