Anyone know if the pro comps 23311 in theory increases an excursions payload? I know legally not to go over sticker. I am wondering cause some sites say that it has the overload spring that increases load capacity (not the pro comp site though).
I emailed pro comp and they were less then useful, just stating, "There isnt necessarily a "weight capacity" so much as the spring rate. Which is 636lbs per inch." When i asked about weight limits.
Any educated guesses out there? Havent found much of any info about any of the pro comps spring capacity. Maybe they are rated worst than oem springs, that would be good to know too.
Anyways just got weighted today and came in at 7650lbs with no one inside, hauling nothing and full tank of gas (2002 XLT 4wd V10). Sticker is 8900lbs. This got me thinking about payload. Thanks.

Fun fact, if i had 9 "average" American adults loaded up with nothing but meat i would be 370lbs or 2 and 1/20th adults over GVWR.

 

A springs weight capacity is sort of arbitrary, it depends on how far you choose to bend it.

since you are the person whom chooses to use this spring that makes you the suspension engineer and the person responsible for determining its operating parameters.

take the manufacturers spring rate info and figure out the capacity.

capacity = spring rate x travel.

 

You make one good point that got me thinking. "I am the suspension engineer".. Well not quite, Pro Comp actually engineered these and published that they are direct replacements. So why dont i just use there already engineered data.
Pro Comp have fitment of these for the 99 to 04 Excursion, F250 and F350. So it would be reasonable to assume that these springs are at least the capacity of the highest load for those three.
Now lets look at that factory data (this is mainly for future me). The rears of the excursion had 5252lbs ground weight limit, the f250 had 6084lbs ground weight limit and last the f350 had 6830lbs ground weight limit.
The rear spring capacity for excursion was 2371lbs per spring and the f350 2998lbs per spring. So IF the Pro Comp 23311 was engineered for the f350 then that would give us a 1254lbs payload increase (total increase rear axle only). Now this is all theory on the assumption that Pro Comp actually knows what they are doing/selling and my educated guess by the reasoning above. The truth is only Pro Comp (might) knows the true load, but they are not sharing.

Now lets keep going with our assumption that the 23311 matches the f350 capacity. From what i have witness there is about a four inch travel before the spring start to touch the load spring. This means 1720lbs (per spring) of the load in the 430lbs spring rate range. Then to put me at matching capacity for the f350 spring i would need two inches of travel in the 636lbs spring rate or 1272lbs added load bring the total to 2992lbs for the single leaf spring. This puts me at the mark and seems reasonable.

Meaning in theory the 23311 would be a 430lbs@first 4"/636@last 2" for a total of 6" of travel and a capacity of 2992lbs per spring.

If anyone has any educated comments or actual facts about this subject it would be much appreciated. Or if i messed up on my calculations.... If you got this far then thanks for reading!.

 

I don't know, but I have pro-comps 6 inch lift on mine, and it definitely has more weight capacity than before, it sagged before with my trailer on, now it really doesn't, if it drops at all its maybe an inch at most.

 

you didn't "mess up" but your travel numbers are off a little bit. the stock f350 spring the 23311 is modeled after has 5" of travel on the primary and 2" on the secondary.
but your aproximation was close.

what I mean by you are the engineer is you are setting the bump stop position and therefore limiting the uptravel which ultimately determines how far the spring bends and equals the capacity.



as you can see by this graph of the F350 rear spring ford chooses to limit the travel at a height of 44mm

the second graph is the stock rear Ex spring, ford limited the travel at 60mm giving a "capacity" of 2371 lbs
but if you set the height to -22 the "capacity' would be 3783

 

springs aside,

the more practical "payload" max on your excursion is determined by the rear ride height, the rear should not sit more than 1.5" below level at static ride height when fully loaded.

since nobody should be driving around with their springs fully compressed to the bump stops and it would be simple to just more spring to keep you at a maximum -1.5" ride height the real limiting factor of "max payload" ( besides your class C license ). is the rear axle GAWR or gross axle weight rating.

 

Wouldn't airbags (which offer a variable spring rate proportional to pressure), be the ideal way to increase load carrying capability?

That way when riding around unloaded or lightly loaded you can deflate the bags and still have a decent ride, but when you need the extra spring rate, you can add air to the bags until you get the spring rate you want for the load.

I had an f350 dually that rode like a freaking dump truck when lightly loaded, and if you hit a bump hard enough to engage the overload springs your teeth would just about jar out of your head and your back would hurt the next day. Took the overloads off and replaced them with supplemental air bags and it helped a lot without sacrificing load carrying ability.

On the Ex I run rear supplemental bags on top of the procomp 22415 springs to level the truck when towing, works like a charm.
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I just dont like air bags, never had good luck with them, always leaked somewhere and when empty still made the truck ride stiff (not an excursion).
And to be honest i am not looking to increase payload of the excursion (main reason to change out springs was to get rid of the 6" blocks), will be sticking to sticker no matter what, cause nothing (even airbags) increases that print. I am more looking for data that i was interested about but havent seen discussed in detail, for education purposes and maybe help someone in the future looking for this info; like me coming up empty handed on my searches.
Anyways there is some good info in here so thanks to those who contributed and will contribute.

As a side note i like how the 23311 rides, its is stiffer than the 20 year old springs i took out (not sure that means much) but i wouldnt say it is rough, firm is a good description. Its funny cause i didnt notice how much bounce the stock springs had until i took the rears out. Now my rears recover after a bump fairly quickly but the front (not changed yet) is still bouncing around. I didnt notice this bouncing with factory all around so guessing the front and back where bouncing together. This is with the same shocks on before and after by the way.

 

yes of course.