Contour Enthusiasts Group Archives Forums Modifications Suspension Why do the stock struts wear out faster?

That sounds like an interesting engineering study. Are you up to funding it? Sometimes that is the only way to get the kind of detail that you would like. Often you can really tell all you really need to know from the experience of others. Experience has shown that if you don't change struts when you install stiffer lowering springs that you will need to do so shortly. That is valuable information. I don't even want to think about how much such an engineering study will cost.

OK. Another non-expert answer. But I read a lot. So bear with me.

Are the hi-perf struts shorter? Yes. Often the shaft is slightly shorter.

Why would they wear out? Well, think about a properly damped suspension. You hit a bump, and the damper goes through one jounce and rebound cycle. Now stiffen the springs. Now the damper goes through several jounce and rebound cycles before hauling in the energy absorbed by the spring and converting it to heat. Add to this that the damper is operating in an area of travel that it wasn't designed for, and... hmmm.

My theory is that your seals wear out faster, perhaps because of the extra cycles cause by almost continuous up-and-down motion.

But I'm not an expert.

I don't belive so since the manufacturers sell the strut to fit the car, so in essence the strut need to be designed to accomodate the viehiclein both stock ride height configurations as well as lowered and in some instances raised.

Here's another possible explanation on why struts wear faster on lowered cars.

When the car is lowered the lowering springs have a higher spring rate (they are stiffer) becasue they need to absorb the movements as the car moves over uneven ground faster to avaoid bottoming out. Becasue of this, the overall travel of the suspenson over a given obstacle is less, but becasue of the stiffer springs the impact is absorbed faster than with the stock springs so in essence the strut is moving in and out faster with lowering springs. The internalas of the strut consists of a small gas charge to help absorb shocks in that it is compressable unlike the oil. The strut's piston has fixed or somewhat variable orifices for the oil to pass through to allow the strut to extend and retract. If the strut moves faster the only way for the oil to move faster is under higher pressure and as Bernoulli's principal explains that as a fluid is compressed its temperature will rise. With that said, while driving, even on smooth roads the speeds at which the strut is moving is faster than what it would be if stock springs were installed to for that reason the strut will have a higher ultimate operating temperature. and under extreme conditions it may get hotter than it was designed for and the rubber seals wear faster, and then the seals wear the oil can leak past lessening their dampening effect and will over time become worm enough to require replacement. Aftermarket or performance struts likely have more durable seals and thats why they are better.

Basic statement 'struts do absorb shock...they 'damp' the spring...the spring takes the 'shock'....

Actually,

Basically, all dampers work by turning motion into heat. In this, they are similar to brakes. Now, consider the brake for a moment. Under normal conditions, the temperature of the brake is pretty low, and pads and discs will last a long time. But on the race track, the brakes are under constant use, and heat builds up quickly. Pads and discs tend to lose performance and wear out quickly under such conditions. In fact, the same thing can happen to dampers as they are pushed to their limit. Worst case, the oil will actually "boil" and cause "shock fade."

Putting uprated springs with stock dampers is a bit like the racing scenario, in that the dampers are going to be working hard all the time, and not given a chance to dissipate or manage the heat that they generate. I think we're on to something with this heat theory, but it sure would be nice to get a real techie on it.

Ok guys. Sounds a little understandable now. These posts have been very helpful. With all the ideas that have been given. I am going to post a little later on after getting ahold from the engineering dept. of a major shock a strut mfg. very soon. I will also research performance spring mfg's and get there insite also.
Once again thanks for your insite.
Steve

Hey Steve, this is an awesome topic. I have asked myself the same question, and I am interested in hearing what a strut company says about this. I understand the working harder part, but I just don't know what part of the strut wears out faster (if it actually does).

FYI - I owned an Escort before the SVT. I put Eibach springs on the car when it had ~45K on it. I later sold the car to my brother w/ ~98K on the clock. At about 100K, he put on some Tokico struts, for the stock struts were finally feeling a little soft. That's about 55K on Eibachs and stock Escort struts.
The SVT comes with Tokico struts...pretty nice struts if you ask me, and they're certainly much more performance oriented than any other Contour's struts.
My theory - Although the struts might not be the correct dampening for stiffer/lower springs, the strut will not wear out any faster.

FWIW, Eibach claims that their springs can be used with stock struts.

For everyone that wants to know what exactly wears out if anything at all; check back next week. By then I will have gotten a hold of some techs. I am going to try to hear from a couple different companies so we get a few perspectives on this. Just look for a new post from me next week lets say by friday.
Steve

Aftermarket springs are lower that stock, they bring stock struts out of their designed base level position, this is minor though.

A stiffer spring has a faster oscillation rate than the OEM one. Hit a bump that compresses the spring 2" and it will bounce back a lot quicker that the stock sping. That faster spring movement makes the strut shaft travel much faster through the body. This can lead to foaming of the oil within the body, as the valving was not designed for those shaft travel speeds to begin with.

This is what people refer to as a "bouncy" or "harsh" suspension setup. There is a bit of aftershock because the damper cannot dampen 100% of the spring's force in a single pass. The spring over-entends so the strut has to have a second take at damping it. A lot more movement there, faster than designed, away from the designed "neutral" position, etc..

I think all these factors are what's taking a toll on the struts. The high speed movement of the damper's shaft puts a lot of wear and tear on the valves. They wear out much faster, letting more oil go by, damping less, letting the setup move even more, etc, etc.. vicious circle that destroys everything within a few months of hard driving.