spring sag consideration

[Xrider237]

for those who have experience w replacing old high mileage springs w new shocks/springs, how much can springs sag over time??

im going to be installing bilstein 6112's on the front and 5160's in the back over the summer...the 6112's come w an Eibach 600lb spring and im going w Icon 1.5" springs in the back..i have a 2003 V8 w 150k easy miles and im trying to estimate how much they have sagged in 12yrs...i want a little rake but not as much as stock

for 2-2.5" lift in the front, should i go w the 1.75" setting or go w the .85"?? my concern is that the new springs might give me 1"+ by themselves and the 1.75" setting will net me closer to 3" where i want to be closer to 2"...likewise, i think the rear will give me 1.5" plus however much the springs have sagged

im trying to avoid taking apart the suspension apart to readjust after the install..any advice or experiences would be helpful- i sometimes think many people underestimate the spring sag factor and end up higher in the front than they wanted/expected

 

[Xrider237]

bump for discussion

*would it work for me to measure my current/stock setup from middle of the wheel to the bottom of the fender..then compare that to a measurement someone took (similar T4R) w fresh springs??

 

[m85476585]

This is contrary to the popular opinion, but I just don't believe that well designed springs with good quality metal will sag over time. Although lots of people will tell you that springs sag, I haven't come across anyone who has pulled old springs out and compared them to new springs and shown a difference. People often think springs wear out faster if you put more miles on them, but I don't believe that either. If you drive 15,000 miles a year at an average of 30mph then the springs are sitting there supporting the static weight of the vehicle 94.3% of the time and flexing 5.7% of the time. And the more highway miles you do, the less they flex. The bottom-out bumpers keep the springs from reaching their elastic limit and yielding, plus the design of the spring inherently does that by having enough coils. You should be able to flatten a spring without yielding.

The charts on pages 242-247 of this paper http://nvlpubs.nist.gov/nistpubs/nbstechnologic/nbstechnologicpaperT362.pdf seem to show that steel does not creep at room temperature. But the paper gets very technical, so I didn't read/understand the whole thing.

 

[Xrider237]

anyone else have any thoughts or opinions on spring sag?? im gonna try and hunt down a stock measurement of an older high mileage V8 and compare w mine

for some reason i feel if i put on the new 6112's w eibach coils at the 1.75" setting i'll be pushing close to 3"

 

[t-man]

anyone else have any thoughts or opinions on spring sag?? im gonna try and hunt down a stock measurement of an older high mileage V8 and compare w mine

for some reason i feel if i put on the new 6112's w eibach coils at the 1.75" setting i'll be pushing close to 3"

Well, once I can get new springs I'll measure mine, but I don't know how long that will be for sure. Could be a week, or even 2 months from now.
With that said, I do believe they sag over time. I have 187k on my truck and I'm sure they have sagged a bit.

 

[Xrider237]

sounds good T- i went back and reread through a couple 6112 threads and saw 2 examples of where guys installed the 6112's and both used the 1.75" setting and saw 2" of lift...so pretty close as advertised..maybe the 1/4" difference was sag- that looks like the ticket for my needs

 

[CXS]

This is contrary to the popular opinion, but I just don't believe that well designed springs with good quality metal will sag over time.

Believe it, read up on metal fatigue which is very real. The thought that springs won't sag is absurd, everyone whose had springs will attest that over time they will wear out and lose height.

 

[m85476585]

If it helps, the factory service manual has specs for ride height.

 

[Xrider237]

If it helps, the factory service manual has specs for ride height.

well thats the obvious 1st place to go for the factory perch adjustments- and iirc are the same as the 5100 series...but ive read in many cases where guys ended up w more lift than they expected..i was just interested in how much of that could be the springs sagging over time and/or heavy use..when asked directly, bilstein stands firmly behind their lift #'s

*awhile back i remember reading about the spring seats (or tophats??) being reinstalled upside down and that would def cause a noticeable increase in lift amount

 

[Rancid13]

I can't comment on whether or not my springs were actually shorter when I removed them because I didn't measure, but I will say that when I installed my OME springs I netted over 4" of lift from where it sat prior. I only had about 88k miles on the stock springs too.

 

[9494runner]

Springs do sag.... my buddy's 1990 2nd gen and my 1994 both had orig factory springs when we got the trucks, both rode almost same height. He put spacers in the rear to get back to stock ride height before I lifted mine. He was 1.5 inches roughly taller than my saggy springs after the spacers. I put ome coils and now I am roughly 1.5 taller than his spacer/stock coil setup. Net gain with new lift springs 2.75 to 3 inches over my stock springs and conservatively at least 1.25 inches over factory rode height after a tad bit of settling and with the weight of the back gear box I built. When I compressed the stock springs it was with little effort. New ones required ALOT more twists on the compressor and a pry bar to get seated.


Metal fatigue is so real. Bend a piece of stiff wire back and fourth over and over it will break in half. Or a soda can pop top... same principle


Edit: And as far as steel goes, there are tons of types... some are more elastic some are more brittal. It really depends on application so it's never apples to apples in terms of steel. Carbon content, impurities, and manufacturing process all affect the steel. With that being said... (off topic) I've heard of people using spring steel for knife blades due to hardness vs elasticity so there are compromises.

 

[m85476585]

A properly designed spring is designed so that it stays under the fatigue limit. Otherwise they would fail. Fatigue limit - Wikipedia, the free encyclopedia If you break a wire by bending it you are causing the material to yield, and you are exceeding the fatigue limit. You can tell it's yielding if it doesn't return to its original shape after bending. A compression spring can't be compressed too far because the coils set the minimum compressed length. Plus the bottom out bumpers keep it from even compressing that far. In a tension spring you could stretch it too far and permanently deform the spring.

Soda can tops are not a good comparison to steel springs because they are aluminum. Aluminum is not very springy, and it fails easily if you bend it enough to make it yield. There's a reason that no one uses aluminum springs. Apparently aluminum has no fatigue limit, but it might be more descriptive to say that the fatigue limit is zero, or in other words even a small amount of cyclic loading will cause it to fail. I'm afraid to go ride my old aluminum mountain bike now!

I'm aware that steel suspension springs sometimes break, but it's rare. I would guess that corrosion and/or manufacturing flaws are most likely.

Leaf springs can wear out because of sliding friction or because some leaves break.

 

[CXS]

Let's get back to this in a couple years and see how your current measurements compare to what you have then.