View Full Version : ZPS, SSD, De-Mystified...

02-26-2003, 08:40 PM
I realized that many people are very confused about what this term (ZPS, SSD, etc...) means.
Simple Definition:
The difference between a spring's free length and it's installed length.

Pre-load can be numerically represented in length, or the weight it would take to compress the spring to that length.

Pre-Load and Sag are not interchangeable terms. Pre-load is often used to control sag, and hence is often confused with sag. On a standard shock (non-ZPS/SSD) Pre-load is set to adjust the sag to the proper ride height.

Zero Pre-load (ZPS) technically means that the spring on the shock is not copressed at all when installed. If this were true, it would basically rattle in it's hardware (loose). Most of these types of set ups are really just shocks that have very soft initial springs that allow for very low ride height, and a lot of sag. There is no specific magic to these shocks, or any sort of special mechanism involved. Most shocks can be set up this way. It's just a matter of using a combination of springs that allow the bike to sag to a low ride level.

Most high end shock companies can set your shocks up to sag a little or a lot. It should depend on what you want. Some people prefer a lower ride height. There are some serious advantages to this. Some people however, prefer a higher ride height. There are some advantages to this as well.

There are some other folks on this board who have a lot of suspension knowledge too. If you feel you can explain this any better, please add your comments. This really seems like a term that is confusing many riders.

02-27-2003, 01:09 PM

dude, you own motowoz!! thats awesome:D

02-27-2003, 04:49 PM
so are you saying that the elka SSD and PEP ZPS spring arn't true zero preload ?

02-27-2003, 04:53 PM
So if ZPS/SSD basically mean the same thing, then:

ZPS = Zero Preload Shock
SSD = ??

02-27-2003, 04:54 PM
zero preload system

self saggin device

02-27-2003, 04:57 PM
yea both SSD and ZPS are the same its just that evertone has patents on those names so they come up with there own

02-27-2003, 05:18 PM
Originally posted by QuadTrix6
so are you saying that the elka SSD and PEP ZPS spring arn't true zero preload ?

Well, here's how you would tell.

measure the length of the springs on the shock. Now take the springs off the shock. Are they longer now? I have never seen a set that truly had no pre-load at all.

Don't mis-understand me. I'm not saying that these shock companies are being misleading. They have a lot less pre-load than shocks used to have, but there is still some. It's just that it really sounds like some people mis-understand the term, and think that it's some sort of special mechanism, and it's not. It's just a term that relates to a certain type of set-up. One with a lot of sag. I guess SSD is really a more accurate term, but I don't know what the "Device" would be (Self Sagging Device)

Basically any shock could be set up this way. It's just a spring set up, and while you can't re-build stock shocks, you can change springs. (This should be done by a shop that has the right tools.) So, even stock shocks could be run like SSD/ZPS. I don'trecommend this, and I don't think this would work well at all, because the valving is not meant to work with that type of spring set-up, but it could be done.

02-27-2003, 06:33 PM
So you have explained the SSD and the ZPS styles of setups, but what the difference in the Limited Mass setup I have heard of.... I believe its PEP that offers these. Just thought I would ask since we are on the subject.

02-27-2003, 06:49 PM
But guys don't think the small SSD or ZPS spring doesn't do anything..like there's no use for it.. It has plenty of use in wheel travel..;)

02-27-2003, 07:06 PM
The zps and ssd springs allow you to run the springs past the zero preload point. That is more sag than at the Zero preload point. I run my axis shocks at zero preload. When the shock is extended there is no pressure on the spring, I can rotate it around easily and it even has a little play letting it rattle around (about 1/16 inch). Now when I put it on the quad it sags to the low ride height I want mainly because the tender spring is soft. But lets say it did not sag enough. Now there is nothing I can do to adjust the sag lower because I am already at zero preload and if I move the clip up any more the spring will not stay on the seat when the shock extends. The only way to get more sag without the zps/ssd spring is to change to a weaker spring. Now if a zps/ssd spring is added I can move the clip up to lower the height (more sag) and when the shock extends the zps spring will keep enough pressure on the spring to hold it on the seat. However the zps spring is so weak that it really does not support the weight of the quad and lets it sag to where you want it.

02-27-2003, 07:54 PM
very informative post, im glad this was on here as i was thinking about this to help me decide between axis and elka. and i called and talked with C&D and talked to axis a little last night. maybe we could put this in the faq?

02-27-2003, 08:01 PM
i agree, put this in the faq. it answered some questions for me!