yup, should be a new thread on suspension basics.

my intent was not to "pick your post apart"

as to why ford only added a anti wrap bar to the Ex i can only speculate since I am not privy to any inside info from Ford but we can examine what they did and figure it out by making some reasonable assumptions

look at that f350 B code spring and the Ex G code and note the differences of the spring pack and how they are likely to be used.

trucks are lighter in the rear but built to haul cargo
excursions are heavy in the rear and built to haul people

the truck has 4 main leafs and a spring rate of 320 lbs in with 7" of arch
the ex has the same 4 main leafs + 2 more for a spring rate of 410 lb in with 5.5 " of arch

now, because the truck is designed mainly as a cargo hauler primary concern is cargo and the overload spring is essentially a very heavy duty bump stop but if you look at it it will keep severe spring wrap in check so in essence it has both.

the excursion being a people hauler is not likely to get loaded like a truck so no need for a overload spring but because it is a passenger vehicle they went with a anti wrap bar that is more effective then the dual purpose overload design.

 

I read somewhere that it was added because of the durability test that was used for the Ex. There was a portion that required the use of low range 4x4 and the wrap up bars were needed.

 

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Even if that is not an official Ford statement it makes perfect sense.

the truck overload spring would have handled the 4 low wrap but neither the truck spring or the Ex spring would fair well in a 4 low high torque load without their respective anti wrap spring.

 

I think those are good points but in my opinion the shorter leaves are stiffer than the longer leafs and the rate does increase the flatter the spring becomes. If that is true then what does the short Ex leafs add to the rate? I would anticipate not much as I'm guessing that most of us never load the back of trucks to get the spring flat. It's possible the spring will go flat while towing over rougher terrain. But statically, I don't think most of us would see it.

The G code Ex spring doesn't have as much arc as the SD springs and that is part of the reason the ride improves coupled with less primary rate. I do believe the spring eye bushings are softer than SD but I've never been able to prove it. I had a coworker years ago who bought an Ex new, it didn't tow very well. The only change he made was the spring eye bushings and it fixed his issue. A sample of one but an interesting thought.

Just my thoughts...

 

your opinion is spot on.

a 3" wide x 24 long .25 thick leaf has a rate of 300 lb in
where a 3" wide 12 long .25 thick has a rate of 2300 lb in.

I was using Fords published spring rate for the entire spring pack of 410 lb in.

an interesting point of matter is Ford list list the Excursion rear spring as
"constant rate" when clearly the pack is actually a progressive rate spring.
technically speaking it is a single stage progressive spring.

they list the F350 spring as variable rate 2 stage even though the first stage is not progressive. it has 2 stages of constant rate springs.

your point of the SD spring riding better, a softer suspension with more travel will ride more comfortable then a firmer suspension with less travel but there are trade offs in ride height and in the case of the Mod B the point is sort of moot since you have added the 2 shorter leafs to the pack and increased the rate back to what the Ex came with. you now have a longer travel and stiffer spring rate spring. net result, same spring rate as the stock Ex with more travel.


long ago I noticed that excursion leaf bushing seemed to wear out and thought maybe they were softer then the truck bushings, but it dawned on Me, the bushings are not softer, the excursion springs are stiffer and the excursion weighs more so that wears them out quicker. worn out spring bushings can certainly be a contributing factor to wander.

 

Plus the Ex has a lot of rear weight and much more roll than a pick up so I assumed that accelerates bushing wear among other pieces in the puzzle.

Great discussion so far! Anyone else?

 

I offer this analogy.

the Excursion G spring has 5.5" inches of travel with a rate of 410 lb in. for a rating of 2225 lbs

the truck B spring without "overload" has 7" of travel with a rate of 320 lbs in for a rating of 2240 lbs

a truck modified B spring with the 2 bottom G springs has 7" of travel with a rate of 410 lb in for a rating of 2870 lbs


the ride between any 3 of those springs and rates does not affect the ride or handling it effects the ride height depending on the load being carried. the "handling" is effected by the shock valving, in general the more spring rate you have the more shock valving you need to control the speed at which the spring is allowed to move.


Now if you add the overload spring to your B-G hybrid pack you are adding 670 lb in to the last 2' of travel for an additional rating 1340 lb in making the total 4210 lbs. ( that is those last 2 inch are referred to as the "bump zone and are not where you want to be in normal operation. like i stated earlier they are really just a heavy duty bump stop in case you "overload" your suspension. in normal every day driving ( even when loaded) you should not be down on the overloads since you have basically run out of suspension travel.

If the goal was to have a "better riding" vehicle you would choose the lighter 320 lb in springs, use lift blocks to adjust your desired ride height which would allow the use of a shock with lighter valving, if you wanted better handling from that lighter spring you would use a shock with more valving.

if you needed to carry more weight ( i.e. at the weight of an excursion instead of a truck ) then you could use the Hybrid B-G with lower 2 Ex leafs giving you the stock Ex rate of 410 but with 7" of travel. again you can use a "block" to adjust final ride height. the same shock valving principles apply here but your base valving needed to deal with the extra 90 lbs of spring rate is going to be higher and that will takeaway from what you can realistically get in the "better riding category" but it will obviously give you more weigh capacity.

now the overload,
I don't see the overload being of any benefit to an Excursion that will be used as a tow vehicle since you are NOT counting on the spring rate it provides to hold up the weight unless you want the rear of your ex slammed down and only and inch or so of travel available to absorb axle movement with that load., if you were designing a rear suspension that could deal with weight beyond what the 7" 410lb in spring provided then Air bags are the best solution for many reasons. but basically they allow you to adjust the rate to the load and they do it in the suspension travel range you are actually needing it. not as a last ditch effort to keep the suspension from bottoming out.they are a progressive rate spring which means the more you compress them the higher the rate will be so essentially they also act as your overload spring if you get down to the bump zone.

that leaves us with the anti wrap bar.
spring wrap is just the nature of the beast of leaf springs. the excursion with the factory anti wrap bar in proper working order does a sufficient job of controlling wrap. Use it and if you find for whatever reason you have a need for more anti wrap control get a set of real traction bars.

 

I would love to hear some theories or explanations of this. I have asked over the years but have never been giving an answer that satisfies me.

fwiw I hear people say that flatter springs ride better just as often as I hear arched springs ride better.

because I don't understand the principle behind it ( if there even is one other then opinions ) I generally don't factor it in, i keep it simple, figure out how much wheel travel I can get or what I want the ride height to be, make the spring as long as possible and then figure out the rate I need to hold up the load. arches will be arches and I'll deal with what ever they are I guess.

 

I have no proof of which spring type rides best, and I suppose one can be better than the other depending on the other components in the system. The shackle can influence the rate/ride but I don't know how apply it with the spring rates.

Seems like an arched spring could ride better because in the same application you could have les rate and more travel vs. a flat spring that would have more because it has less travel. Perhaps my perception is closed by my experience.

 

as far as I can tell the shackle angle therory comes from when somebody sets one up wrong and it goes inward towards the axle or as we call inverted and binds up, but any angle from vertical 90* to 45* or horizontal level will not change the spring rate or effect its ability to move.

I think you are correct that it has just become people's perception over the years and they have just come to equate arched with more travel and perceive that as a better ride. ( even though you can easily make a arched spring give a empty dump truck quality ride)

 

Hey guys,
I am still working through this never ending project. My next step is front shocks. So I have front Ford x code springs.. seems that every is saying that the stock size f250 shocks are the way to go up front. I am confused because according to the Bilstein website, they are the same model # for 0-2.5" lift shock 33-187297) . And there is another one that is for 4-6" lifted height(33-185545). I took a set of China x codes out of the truck so it is hard to tell the overall stock to mod height change. What bilsteins are you guys running?

 

That's the one you want...