Way soft suspension - arrg!

[koldsimer]

Common sense tells me that the more arch a spring has in it, the more it is affected when it gets into negative arch. Ask any spring expert, negative arch is a BAD thing with lift leaf springs. Sorry Triaged, but i'm gonna have to go with what BDS, Alcan, Deaver and Tuff Country all say about their leaf springs. Negative arch is bad for them! As a matter of fact, I lost about an inch of lift on my driver side when I let the spring compress too much. Did the spring break ? no. Is it any weaker... probably.

 

[79k20350]

Again if going to have to vote for no negative arch. it strains the spring, it may not break it but it wont be the same.

 

[steve_kibbe]

I didn't vote because I agree with getting the skyjackers because you have a BB and a winch. I think in your circumstances you will need the extra spring rating.

Just my .02

 

[Stephen]

1st, the main question and my answer (educated opinion?):
If you want more ride height, put in the HD TCI bottom leaf (we have them and this is somewhat common) and if you want more bump resistance, use a stiffer shock. Spring just hold the truck up, shocks provide higher speed impact resistance. If the shocks or mounts won't take it, get better parts, they're out there.
To lead into the 2nd part of this, you're doing the right thing limiting the bump travel, the ONLY problem with using a EZride type spring with a lot of weight is that you take up the springs available travel just getting to ride height. Then you sit there right next to the bumpstop and can't go farther before you overstress the spring. The only way to find more bump travel is a spring with the same rate and more available travel or a stiffer spring.

I'm going to go with the bull**** call on the negative arch myth. I've designed and run many springs that go to negative arch and they don't self destruct. This is where some understanding of how a spring works comes in handy.
1: Steel has a yield strength under which you can bend it over and over and it will never stay bent. This is where any spring (coil, disc, leaf, whatever) SHOULD operate and if they are used in this stress range, they last indefinitely.
2: When you exceed the yield strength of the steel, it bends permanently.
3: Any spring will have a load that it can hold without bending, this is the capacity. This capacity is reached at an amount of compression travel determined by the material and configuration of the spring. When this capacity is exceeded, the spring bends, it's overstressed.

Just for an example, if we have a spring with a max capacity at 6" of compression and put enough weight on it to compress it 3" at static conditions, you have 3" left to play with. Now put on your bumper, winch and big motor and compress it another 2". The spring's limits have not changed so you now have 1" of bump travel to play with.

None of this has anything to do with how much arch the spring has at any point in it's travel. Negative arch works just fine in reasonable amounts. As stated above, some springs ride level and any bump travel is in the negative direction.

Most people's problem is simple overcompression, run bumpstops so they don't over compress and you will never lose a leaf spring, at least not due to that problem.

More thinner leaves are the answer because the stresses are lower in each leaf but they cost a lot to build that way.

 

[Mammoth2]

I a thicker sway bar an option

 

[Blue85]

Stephen seems to be the only one looking at things logically here. You should be concerned about how FAR the spring bends and how much LOAD is on it, not whether the arch is positive, negative or whatever. Obviously if a 12" lift spring is bent into negative arch, it will have had enough load and bend in it to hurt it. A 1" lift spring probably runs about flat. Should the suspension prevent this spring from any uptravel, any downtravel or both? The spring steel doesn't know whether it is forming a positive or negative arch. It only knows its set point and how far it is being deflected from it.

This is assuming we are talking about leaf spring durability. There are other cases in suspension design where negative arch has to be avoided because it lets a shackle flip over and lock the spring in some horrible position or some other hideous problem. Ideally this would be fixed with different geometry, though.

 

[79chevyk10]

Stephan's the man. That boy know's his chit. I'm gonna call bull**it on the negative issue also. I run my both my front and rear springs to go negative. Just slightly though, my front I let go slightly negitive for 3 years now with no problem and zero ride height loss. The rear I flipped the overload and under full compression the are negitive about an inch before the bumpstop comes into effect without any problems as of yet. FYI, 4" springs front and stock 1/2 ton 56's rear.

 

[koldsimer]

Yes, we all know that Stephen knows his stuff. The $$$ I have given him for quality parts shows that I respect his opinion on many topics. However, if negative arch doesn't effect your springs, why did I lose almost an inch on my left front spring after I was over flexing it in a ditch. After thouroughly examining any other possible causes, my best guess is that the inch or two of negative arch that my spring went into caused it to lose some if it's lift. What else could explain this. So bullsheet to all the bullsheeters who call bullsheet. Negative arch DOES hurt my 6" lift BDS spring.

 

[Stephen]

Kold', I'm guessing that if you measure the arch at ride height on your BDS springs, you're going to find it's about 4" or so, maybe a squeeze more. Compressing a stadard aftermarket spring 4" is about all they can take. It may be good for a bit more but that's a matter that takes some closer calculation. So it is probably a matter of over compression again. Just because none of the lift manufacturers tells you about a bumpstop spacer doesn't mean the spring is designed to run without one. Often they count on the capacity of the spring being the suspension's limit so basically you can't put enough load on it to hurt the spring. 20 years ago this was a good strategy. Now, we load up a bunch of heavy stuff and try to get the truck teetering on 1 or 2 wheels so a capacity limiting spring will probably not work in the front. Luckily rear springs with the overload have pretty big capacities so they self limit pretty well without a bumpstop.

There's also room for material defects, at high stress levels, it doesn't take much of a problem in the steel to show up.

 

[koldsimer]

Kold', I'm guessing that if you measure the arch at ride height on your BDS springs, you're going to find it's about 4" or so, maybe a squeeze more.

Exactly. Just under 5".

Compressing a stadard aftermarket spring 4" is about all they can take. It may be good for a bit more but that's a matter that takes some closer calculation. So it is probably a matter of over compression again. Just because none of the lift manufacturers tells you about a bumpstop spacer doesn't mean the spring is designed to run without one. Often they count on the capacity of the spring being the suspension's limit so basically you can't put enough load on it to hurt the spring. 20 years ago this was a good strategy.

Good points... with my 6" Pro-Comp springs I was never the least bit concerned that I would lose more than an inch or two of lift, ever, no matter what I put on the front of the truck. Negative arch? Yeah, right. Right now I have my stops built to stop the spring when it is completely flat. On the passenger side, I have had the spring flat on the bumpstop and it has never lost any ride height. To me, negative arch is when the spring center moves above the eye to eye centerline. Is this over-compression? For my springs, yes. I think it is misleading to the average person when you tell them that negative arch doesn't hurt your springs. Would an 8" superlift spring be fine after it sees negative arch? I think we are over-generalizing the problem here... too many application specific variables to take into account to say neg arch is good/bad. So... I still believe that negative arch due to over compression on most 4" plus lift springs is bad for them. Ah, bullsheet. I guess we are both right.