I feel stupid. This should be obvious. Load Rating for a Leaf Spring.
Is it the absolute maximum load the spring itself can carry?

The rear of my van weighs 4080lbs loaded for a weekend trip.
The load rating I need for each rear leaf spring is then
(4080lbs - unsprung weight) / 2 + safety factor ?

And I guess always take one up rather than one down. Or am I overthinking this?

 

Picking the spring rate a matter of how much sag in the ride height you want with no load vs full load, plus some margin. I know this well for coil springs, but I don't have experience calculating for leaf springs.

 

Oh it would be so much easier if the manufacturers would specify the spring rate for the leaf springs! Or a force/deflection curve since leaf springs are slightly progressive in nature.
Spring rate is a term I am familiar with. Load rate on the other hand is a term I do not know.

 

Talk with a knowledgeable spring shop or manufacturer to get their specific recommendations based on your real-world or anticipated use of your particular vehicle. That way there's no guessing, calculating or guessing what to use.

Terminology can be helpful or problematic depending on who uses it and who hears it.

 

I would talk to a local knowledgable spring shop if there was one.
I was hoping that "load rating" had some logical meaning, but I can't find what it means.

 

I'd not typically recommend buying springs over the internet ( = shipping costs) but maybe contact Junior at the ATS spring shop---they're a sponsor here on FTE.

 

I may order the springs through a local shop, but I still need to know what to buy.
I only need to know if "Load Rating" refers to:
A) The weight as measured at the tire-ground surfaces (like GAWR)
B) The weight on the leaf springs, unsprung weight excluded. (Most likely)
C) Payload? (Probably not.. but some google results point to that anyway)

 

Repeating myself contact Junior at ATS spring shop---almost certainly he'll have an immediate recommendation for you. @ATS Junior

 

Thanks, already did

 

Springs are one thing, but what is the axle rated for? That is the final determination of how much you can carry. No sense having 4k of spring on a 3.3k axle?

 

You are right. I am overloading the axle a bit, and have done that for a long time. GAWR is 1723kg (3800 lbs) 🙈 Ford 8.8 axle. Not good, I know.
I ended up purchasing the 2250lbs "heavy duty" version instead of the standard 1685 lbs version. At least now the leaf springs can match the load capacity of the axle. Right?
Haven't installed them yet though.

 

@refur Did you already install the heavy duty 2250lbs leaf springs?
What is your experience with them loaded vs unloaded?

 

Hi iaacek. Yes I did, and they are just perfect! Rides so much better. The van is level when fully loaded.
I never drive the van completely empty, there's always some load in it. But I think it would't be too bad empty. The original springs are very weak. I think the E250/E350 springs might be too stiff.