From what I under stand, preload can also be used like limiting straps on your suspension. I have heard of pleanty of drag racers that us4e limiting straps to make the front end hook up better, and if you reduce your shock droop (with added preload like stated in the above post) you will effectively have limiting straps.

This "limited droop" is probably what motor cyclists use to tune their suspension (expecially in moto cross)...

Just make sure you don't add too much preload/shock travel, or your UCAs will smack the shock tower over nasty bumps on the street...

 

I have never heard of preload as anything other than what holds the springs in the seats when the suspension is at full droop. I'd love to hear someone try to explain why preload is good for handling other than keeping the springs where they should be at full droop. Take your 2000 lbs car with perfect weight distribution and preload you 500 lb/inch springs a full 1 inch.... then when you set the car down, the springs won't compress at all. That'd be good. haha.

I hope that's not too sarcastic for anyone...I'm just having fun with this idea. Crazy.
Chris

 

I find that preload is very important for stiff linear springs... Or I should say very short stiff race springs that doesn't compress much at all even if the springs are supporting the static vehicle weight (per corner).

On regular street springs, the springs will never "pop" out during bumps and the suspension wil never be at full droop. Since the springs probably compress about 2-3" when the vehicle is settled down, it is impossible to pop out the spring unless we plan to do some rallying with jumps 10 ft in the air...

On race springs however, the springs could potentially pop out if they aren't preloaded. If there is a "gap" between the spring and the purge when the shock is fully extended (full droop) yet the springs barely compress when the vehivle is settled, the springs will pop out over a pothole.

I noticed that if I do not preload the coilovers on my Camry which uses 15kg/mm springs on a McPherson strut, the suspension will make this nasty popping sound whenever I hit a pothole (not a bump, but a pothole which the wheel would drop down). The car does become more bouncy as well after preload from my experiences.

 

Yes, I agree with preload to keep the spring in the seat, but that's all. There is talk of preload beyond that it seems.....either that or people are thinking that what people are talking about when they say preload. Anyway, that was a good explanation of why you want a little preload.
Chris

 

There is an interesting effect if you preload quite a bit on springs that aren't that stiff. When you corner, your outside ride height will be the same as without preload, but the inside will actually be lower, lowering your total ride height. Now the transient effect of your suspension stopping unloading I don't know about for sure. And this effect would be miniscule on stiff springs. But it is interesting to think about.

 

Adding mucho pre-load can have the same effect as adding limiting straps. Good thing for drag racers I guess...

 

Preloading is exactly what it sounds like: the amount of load that the spring has on it internally before an external force is applied. This is important for limiting the amount of initial travel. For instance: If a spring has a 600inch/pound rate then it will compress inch per 600 lbs. If you preload the spring by compressing it one inch, and that is the static normal condition of preload, then one would have to overcome this amount before additional travel occured.

So if a car is evenly weighted, and weighs 2000 lbs, and has (for simplicity) 500lb spring rates, then it would sag initially to one inch compression. if the springs are each preloaded to 550lbs, then the car's suspension would not travel until the additional 50 lb amount in each spring was overcome.

The problem with preloading is that it usually tops out the suspension quickly and causes premature failure. Some shock manufacturers overcome this with a negative spring that allows for travel beyond the neutral position. This can sometimes be adjusted also to predict the nature of the topout.

 

I've never heard of preloading causing premature failure. Is this due to extreme cases of preloading?

 

the preload, perse, does not cause the failure. The topping out does cause the failure. You will destroy your struts if the preload is excessive, and you dont have the valving to control it.

 

now i completely understand, thanks partsquest.com

 

WOW - This turned out to spawn all kinds of opinions. I'll touch on a few that I can recall reading, but first I want to answer the question about travel or more specifically Maximum Compressed Travel.

Before you can set your ride height, you should know a few things about how your suspension works. Most enthusiasts just go for how cool it looks with a 17, 18, 19 or 20". This method of setting ride height is simple and aesthetically cool. But I've seen many cars with bent wheels, fenders and struts because a few key elements were missed. I'll explain how to permanently fix tire rubbing later.

It is paramount to know how far in compression your suspension will go before parts start bending. When a shock manufacturer determines the length of a shock, they need to know how far the suspension will be allowed to travel both in droop or extension and more importantly in compression or jounce. They do this by removing the spring from the shock and compressing the suspension. They do this to find out when the ball joint, tie-rod, sway link, etc. are maxed out. They know that if they allow a shorter shock body, they may break some parts.

Now to jump over to Racing - no one cares if you break you car by setting the ride height too low or bend parts from not running bumpstops. These are race parts and don't carry very good warranty if any.

Actually they do care, but have no idea what settings people need for their various racing or street applications. Are you going to street your race set-up, rally it, autocross, road race or just show it. Is it to be used on a smooth track which doesn't require a lot of suspensions travel, or is it on a typical road course or canyon road that has pot-holes, dips, bumps,etc. This is one reason the adjustable body shocks are getting so popular.

I'll follow up with a procedure on how to determine the proper shock length in a little while.

For now, post what problems you are having so I can touch on a solution.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike-y &raquo;</TD></TR><TR><TD CLASS="quote">

heh, think of it this way.. I used to have a set of tein flex's, which are the same adjustable shock body design as teh omni's.

now when I first installed them, the springs would compress about 2" up front under the weight of the car, and decrease my shock travel (which is very limited on this design of shock).

adjusting the lower shock mount would raise the car, but I could still bottom out the front shock on tight, low speed corners.

So I preloaded the front springs 1". this gave me 1" more shock travel because instead of the spring compressing 2" under the weight of the car, it only compressed 1" (and raised the ride height 1" as well). I then used the lower shock mount to lower the car 1" back to the original ride height. this helped a lot from keeping the shock from bottoming out.

I did something similar with the rears too, added some preload to gain shock travel. but adjusting these things is a major pain in the butt, since you have to undo the lower shock mount to make height adjustments.

EDIT: if you would like some good information on preload, there are a lot of motorcycle websites that cover this topic. It seems like a lot of moto-x guys use preload to help tune their suspension setups.</TD></TR></TABLE>

This is probobly the best explaination so far.

On the topic of MX, we set the preload of the shock to dictate the sag (the amount the bike sags with the weight of the rider on it). (Full size)MX bikes have a general rule of thumb that you want a difference of 100mm of sag (measuring from r. fender to r. axle) between when the bike has no load on it and when the rider is sitting on it.

Ive been thinking about sag on cars a lot lately. First, I thought that, in a car's case, having preload was just a measure to keep the spring in place. Then I thought that, if the spring had more preload on it, the car would sag less once resting on the ground. I think this has a larger effect on performance than most people realise. It seems to me that if the spring is preloaded more, the ride will be less plush, because the spring has a larger load already on it. If the spring is hardly preloaded, it will be more plush.

Im not sure if thats acurate, but it makes sence to me.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by moto27cm &raquo;</TD></TR><TR><TD CLASS="quote">


On the topic of MX, we set the preload of the shock to dictate the sag (the amount the bike sags with the weight of the rider on it). (Full size)MX bikes have a general rule of thumb that you want a difference of 100mm of sag (measuring from r. fender to r. axle) between when the bike has no load on it and when the rider is sitting on it.

</TD></TR></TABLE>

Out of pure curiosity, on these bikes, what springs are you using?

 

You know, I dont know what they come with from the factory. They arent marked with any type of brand at all. I guess they are just made, or sourced out by Kayaba or Showa, etc. Aftermarket replacements include Race Tech, Progressive Suspension, WP, Eibach among others.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by moto27cm &raquo;</TD></TR><TR><TD CLASS="quote">


Ive been thinking about sag on cars a lot lately. First, I thought that, in a car's case, having preload was just a measure to keep the spring in place. Then I thought that, if the spring had more preload on it, the car would sag less once resting on the ground. I think this has a larger effect on performance than most people realise. It seems to me that if the spring is preloaded more, the ride will be less plush, because the spring has a larger load already on it. If the spring is hardly preloaded, it will be more plush.

Im not sure if thats acurate, but it makes sence to me.</TD></TR></TABLE>




Thats pretty much what I experienced.. more preload = harsher ride. and on the rebound coming off of big bumps, the shock tops out, and launches loose items in the rear of the car up in the air The only reason I needed preload on this setup was because of the particular shock body design. this type of setup with an adjustable shock body have very limited shock travel compared to a traditional shock. there is very little total droop, and you are only working with a few inches of total travel, so preload becomes more of an issue.

a traditional shock/spring setup like a koni/GC won't need preload and is a lot easier to adjust height, since you are only working with one adjustment point.

 

Good to see that you're using the RaceTech stuff. I can recommend the Factory Connection parts as well.

Ryan

 

I agree. Im actually running Type Flexs as well. I do think that preloading is important on any type of coilover, but understand that with non-shortened stroke shocks, you cannot preload without raising the car.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtecvoodoo &raquo;</TD></TR><TR><TD CLASS="quote">Good to see that you're using the RaceTech stuff. I can recommend the Factory Connection parts as well.

Ryan</TD></TR></TABLE>

Yeah. Ive not used Factory Connection, but Im sure their product is quality. There are so many different suspension tuning companies in the industry, its hard to choose. I have had revalving done by FMF, Race Tech, and a few local companies, personally.

 

[QUOTE=Thats pretty much what I experienced.. more preload = harsher ride. and on the rebound coming off of big bumps, the shock tops out, and launches loose items in the rear of the car up in the air The only reason I needed preload on this setup was because of the particular shock body design. this type of setup with an adjustable shock body have very limited shock travel compared to a traditional shock. there is very little total droop, and you are only working with a few inches of total travel, so preload becomes more of an issue.[/QUOTE]

This is a defeatist situation. In order for your car to handle well, the tires need to be touching the ground, if the shock is topped out when you go over a bump, the weight of the car yanks the tire off the ground, or at least tries to. Topping shocks out has some benefit in limited racing applications, but doesn't really work well on the street.

In thee comments from several people is the key to the term "PRELOAD" it can only be done with the shock fully extended. If you Pre-load the spring enough, you will drive around with you shock fully topped out all the time. Not the best.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by partsquest.com &raquo;</TD></TR><TR><TD CLASS="quote">
In thee comments from several people is the key to the term "PRELOAD" it can only be done with the shock fully extended. If you Pre-load the spring enough, you will drive around with you shock fully topped out all the time. Not the best.
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This is where it gets interesting. I agree with this. Im wondering where (if at all) the happy medium is. What is the best way to determine whether or not your damper is tooped out?

Logical reasoning says that, for your damper to be topped out, the car must not sag at all once rested on the ground. Thats a hell of a lot of preload. Enough to support the whole car.

 

I just talked to BOB over at OMNIPOWER USA and he said you really don't need to preload the 12k or 18k setups. Also said it is only focused on to maintain correct suspension geometry!!

 

12k and 18k are very stiff rates, you are talking about 672 lbs/in and 1008 lbs/inch, I'd hope you don't need any preload!!

The teins came with 9k/4k, which is about 504/224, and I think I was actually runnin 8ks in the front, so there was definately some sag or settling going on if I didn't preload. There would be very little if any sag due to the weight of the car if you ran 12k/18k springs. which brings me back to my point about this shock design not being ideal for cars with "streetable" spring rates.