GhettoRacer

We use body length adjustable shocks too actually. :-)

Matt Romanowski

It's not inherent in the design, but people are making shocks that can be droop limited now. Coming off this dumb cold I can't remember anything, but the guy that works with Stimola is selling a line of shocks that has Penske internals in a standard looking Porsche front strut setup. That could easily be droop limited. Almost any rebuildable shock can be droop limited with spacers inside the body on the shaft.

SundayDriver

Sorry? What does that have to do with the stuff you posted? I don't see where he ever talked about true preload.

SundayDriver

That is interesting and I am not surprised that someone is doing that. But how practical can that be on a production car? Wouldn't you have to be able to easily change the limiters anytime you change the ride height (or even set the ride height)? I guess it would make sense if you were doing something like 25mm of droop - it would not be a big deal to be off a few mm. But it seems like it would be very time consuming to try to do zero droop with that.

BTW - There are some more great insights on the DSR thread referenced above. Pay attention to both Richard Pare and Ren.

GhettoRacer

Wow, that is a super useful thread in there. Thanks for sharing! I now understand the true function of preloading. Very sweet. Hmm, my copy of Vehicle Dynamics is sitting at home and I haven't flipped that book in like 2 years... time to read what Paul has to say on the subject again...

kurt M

GR, please. You have two very popular threads of your own. Please let the rest of us digital mortals chat about and read up on interesting stuff without unwanted interruption. We don't care if you had the book for two years. Keep in mind that it is not you personaly it is the fact that a lot of us have the book in question and the thread would drag down if we all pointed that fact out.

RedlineMan

Now, back to our regular programming!!!!!!

I'm not smart enough to wrap my tiny brain around this stuff. I'm not sure it makes much of a difference on anything but a finely tuned lightweight car. But I may have some pertinent insights.

I know from my work wit 944 owners trying to avoid re-indexing their torsion bars that preload is important. Sometimes you can get sufficient rear coil preload by just sagging the ride height eccentrics, and sometimes not. When you do not have sufficient preload, transient handling suffers. Not only is there audible clunking and banging as the coil springs seat/unseat, but this does seem to make the transient handling somewhat less predictable than would be desired. I realize this is not directly germain to Mark's question, but it is noteable nonetheless.

Also, as Larry briefly eluded to from the bicycle realm, preload, or more accurately sag, is important to shock function, and I have a hunch this may be at least part of the issue here.

As a for-instance, my Santa Cruz Heckler (5.5" front/rear travel) has a FIVE way adjustable Progressive Suspension 5th Element Coilover rear shock; 1) spring preload, 2) short stroke (high speed) compression, 3) long stroke (low speed) compression, 4) rebound, and 5) what is called Stable Platform Valving, which cancels low amplitude, low frequency oscillation (peddling forces).

These shocks require a pretty healthy amount of sag (upwards of 20%) to be set in a static state for proper function of the system. You need to access some portion of the positive travel of the shock in order for the damping circuits to function optimally, both in the positive (compression), and negative (rebound) portions of the stroke. Could this be what the car people are tweaking when they have a preload variable vehicle?

GhettoRacer

bah, kurt there is the ignore function. learn to use it. it's pretty good. you don't see me responding to VR anymore do you? back on topic.

FWIW, the coilovers on the del Sol are not valving adjustable. however it does have adjustable body length feature as well as spring pre-load adjustment. it is short stroke and is droop limited (not sure if it's by design or by product of short stroke?). the shock is mono tube pressurized design. if there isn't preload on the spring, the car handling feels a little "floating" like... so the manufacturer recommends like at least 1/4" preload. i'm not really sure if it is used to fine tune handling like that thread suggests... at least i've never heard of it on production cars.

Larry Herman

I am not certain that what you are referring to is suspension pre-load. Having the spring sit tightly in the perch is not the type of pre-load that this discussion is talking about. It is having enough tension on the springs so the car does not compress the suspension at all when it is sitting on the ground. That would be the starting point for zero pre-load. Now compress the spring further and you are adding pre-load.

SundayDriver

Since you are spreading your nasty, attacking comments beyond your own threads, I have to say that is the best idea you have put out there for us. You used to be fun - no longer. BYE, you are on my ignore. I can only suggest that others do the same.

Matt Romanowski

It would be a pain, but setting the shocks is pretty easy. It's just like a regular 911 strut body with Penske Internals.

Sorry for the mixed up response before. I'm working through a nasty cold/flu things and geting better. If your interested in the racecar shocks, call Stimola. He rebuilds everything and can probably give you some good info. AMF in NH is also really good on Ohlins (I think Konis and Bilsteins too).

Thanks for the links.

richard glickel.

Larry, John, et al.,

Mechanically, how does one go about adjusting the pre-load (or load) on the springs before including the shocks in the equation? (Not sure if I've stated that correctly). Is a particular type of lift or jack(s) required?

SundayDriver

Remember that preload requires zero or limited droop. With the car raised (or the shock out of the car) you tighten the spring perch until there is no slack. Preload is then normally measured in turns or flats. So if you have 12 thread per inch threads on the shock and 500 lb springs, 6 turns would give 250 lbs of preload.

richard glickel.

Mark,

Thanks for the easy to understand explanation. I have no immediate plans to try this (and may never give it try), but I now understand what's been discussed here.

GhettoRacer

as long as the spring is compressed some, most ppl call that pre-load as the spring gets compressed. zero pre-load is interesting to me though... i'll have to think it through some more... very interesting. hmm......