How important is preload?
 

I am in the process of replacing my front 200mm 6kg springs with 150mm 8kg springs. Unfortunately the coilover I am using adjusts height and preload at the same time.

Doing a straight swap of the springs without any other changes makes the car sit about 10mm lower, even though the new spring is 50mm shorter. What does change dramatically is the preload - the new spring can rattle around when the car (not wheel) is raised more than about 25mm. With the old springs fitted they were always slightly loaded.

I'm guessing a raised ride height with more preload would be better than the current situation?

The car is only used on the track.

are you saying that when you jack the car up just 1 inch, the springs already unseat from the tophat?

Sounds to me like you have done a bad job adjusting the correct length of your shock body. You need, at this point, remove the term "preload" from your vocabulary and really start understand how to adjust your shock length and spring perches for optimal performance.

It's the Tein SS, you can't adjust the shock body.

I'm guessing ideally I should use a helper spring?

okay. well don't be afraid of preload. the ricer market has put a stigma on it.

Let's just say you'd have to raise your spring perch 4.5" inches before you need to worry about the negatives of preload.

Right now, if you raise your spring perch you will gain both bump and droop travel (since the spring is more likely to be seated).

Yeah I was more worried about lack of it. I assumed it was important to keep the wheels firmly on the ground through all conditions (droop travel is probably what I mean).

I'll raise the perch 10mm then get a more accurate measurement of when the spring starts getting really lose.

So, is this what you're saying? Because that's probably not good as the car will move around side-to-side more than 1 inch.

real racers have loose springs.

you can optionally ziptie the springs to the top hats if you have the right holes in the top hats. the lower part of the shock will self-center the spring.

a HELPER (not TENDER) spring (super low spring rate, can squish with your fingers) will prevent the loose springs but cost you an extra $200 for all four plus spacer blocks.

You want to screw the lower adjuster all the way in, to give you as much travel as possible. You don't need a tender (whatever you want to call it) to hold the spring tight, it won't come off the perch when you're driving if you have a sway bar.

read page four

http://www.ksportusa.com/edocs/Coilo...structions.pdf

1. those are horrible instructions. Ricer company K-sport, is case and point why I say they give preload a negative stimga.

2. he doesn't have adjustable shock bodies.

i promise k-sport doesnt have me on their payroll but im just curious on why you say they're ricer. Also, never said preload was bad. however, i do think its not something to do half hazardly and can upset a car very easily.

IMO ksport = a very cheap knock off version of stance coilovers. For the baller on a budget

lol @ anyone knocking off Stance. What makes Stance so great?

the price lol

KW would be a better example i guess... still too rich for my blood.

Good point about the swaybar. I'll jack the spring perches up a bit to try and remedy the issue a bit (and buy me more shock travel) but it will always be at the expense of increased ride height.

I think I should stop throwing good money after bad and save my $ for some XIDAs or Mono Flex. :)

Xida and twin are not remotely close to the same category.

[quote=v01canic;791254]i promise k-sport doesnt have me on their payroll but im just curious on why you say they're ricer.[quote]

Because ksport makes a very cheap knock off version of stance coilovers. They provide products to be baller on a budget.

and they do suggest preload is bad, the tell you to setup the spring so it's at zero preload, then go on to tell customers to adjust the height of your suspension by adjusting the shock body length up and down and always maintaining zero preload.

this is how a ricer company without any knowledge in the subject would tell someone how to setup a suspension.

you dont think adjusting the shock body length haphazardly will have negative effects?

Not that I know better, but I'm curious why you think adjusting shock body length would be bad?

Ideally of course the threaded sleeve/area of the shock would just be at a correct location to allow proper adjustment of the spring.

At zero-preload, you have essentially setup your shock with the minimal amount of bump travel available to it. So right then and there your suspension has servely suffered a negative strike against it.

Let's say you followed KSport's instructions, set the spring at zero pre-load and threw it on the car and the setup was too low -- which is will be. In order to raise the suspension, they tell you to adjust the shock length.

When you raise the car this way, you are raising the car in relation to the wheel, so the bump travel still remains as limited as possible.

Why in the world would you want to limit bump travel, especially in a miata?


Now also, think about what happens when teh shock body is too short...The tire can easily hit the fender well before the bumpstop is fully compressed. So let's say that you set the spring to zero preload, toss it in, and you're happy with the ride height. But let's also say in this situation, the tire rubs the fender wall. Now you've limited the bump travel even further than before.



In my instructions, I would instruct the user to set the shock body length in such a manner that you were certain that the tire never made contact with the fender. This would be the minimum length I'd instruct a user to allow the body to go. (Acutally my coilover kit wouldn't have adjustable bodies, I'd determine this length for them -- like Xidas) Then I would instruct the user to then set the spring so it's at zero preload and if the setup is too low, which it will be, then to raise the spring perch in order to raise the car. Yes, I know there are certain limitations to doing this, but it only is result of excessive preload due to too short of supplied springs from vendors that do not design the shock around the application as with 99% of the adjustablee shock body coilovers out there: ksport, stance, tein, etc.

But. When you raise the car in this manner, you are raising the car in relation to the spring perch, so you actually gain suspension travel. You are moving the resting position of the positon higher up within the shock body, exposing more shaft, adding bump travel.

MY coilover kit would also have spring rates and lengths coupled with the shock, so you know you will be able to balance the shock length and spring perches, in such a way to acutally dial in your ratio of bump:droop travel for optimal performance.

maybe you should take a second look, with these coilovers you are never adjusting the travel of the actual damper. That would be counter productive. The damper actually maintains its length and when you raise or lower the car the entire damper actually moves within the coilover body. Also the damper is actually valved according to the spring rate.


If you have to adjust preload to cross-balance/corner-balance your car, youre fixing one problem by causing another.

The Grand-AM Riley chassis I worked with set preload via a conventional threaded spring perch. The ride height was set adjusting the length of the upper shock mount in the chassis. Many Touring and GT cars still use just the threaded spring perches to adjust ride height, which does effect preload. I personally would not worry about pre load to much given what I have seen. If you can avoid it then do but I wouldn't stress.

Wheel travel is determined by spring length, shaft length and room in the wheel arch. It is also not uncommon for a race car to unload the springs completely in droop. This can be used to tune the cars roll and pitch.

You shold take a look at the diaphram/shaft within the shock and the relation it has to the position of the shock mount.

I agree, you cannot adjust the total stroke of the actual damper, but you can servely limit the amount of useable stroke available -- you are adjusting where the diaphram within the shock resides at rest.

At zero preload, you are ensuring that the diaphram is nearly at the bottom of it's usable range, which means the shock will bottom out quickly (ie. little bump travel). Look at a straw in a cup, pull the staw up so the bottom end is closer to the middle of the cup and this illustrates my point.

When you add preload, you push the top hat away from the shock in relation to the spring perch. This moves the diaphram higher within the shock itself and you've gained bump travel.

Now, take that same straw in a cup, push the staw down so the bottom end is nearly touching the bottom of the cup.

Which will dampen bumps more? Then one that has plenty of stroke available to it or the one that's nearly at the end of the stoke?

Now to illustrate how lowering the bottom mount would be, would be like setting the cup down on a coaster...the top of the cup sits higher up than before, but the straw still is almost touching the bottom.

When you lengthen the lower mount, you are technically pushing the wheel away from the spring, and gaining ride height there with the extra distance you've created there. The bump travel available is never changed -- the amount of useable stroke stays the same, and it's at the low end of the scale...but you have TONs of droop travel.

saboteur,

A couple things on the springs you installed. I am assuming you have put them on all 4 corners. The reason the car only dropped 10mm instead of the difference of 50mm is because of the increase in spring rate. What is your current ride height to the pinch welds at the jack points? How heavy is the car? The only thing that limits droop is the free length of the shock.

that's not true either.

when you increase preload, you reduce droop. likewise, when you shorten the shock body, you reduce droop.

Yeah, that is definitely the reason it is sitting higher, I just mentioned it to 'complete the story' so to speak.

An update and solution: I wound the perch up until the spring had no play when unloaded but it resulted in the ride height looking like that on a rally car. So I played with the height a bit more and found a compromise that wasn't too crazy - it left about 20mm of spring play at the unloaded free length of the shock, with an acceptable ride height & shock travel. Here is a quick pic to give you a rough idea on height:

https://www.miataturbo.net/attachmen...ine=1320365671

If this was a street car ideally I'd be looking at helper springs, but on the track I doubt I am ever going to have the suspension unload enough for the spring to get loose taking into consideration the swaybar helping etc. Time will tell!

Cheers

Braineack,

You are correct. We are talking about the same thing. I will try to break this down to the best of my knowledge so all can follow.
Look at the suspension on one corner as 3 separate pieces:

1. The wheel, and control arms for simplicity.
Droop: This is limited by the bushings binding or the control arms hitting the frame or binding.
Bump: Limited by the tire hitting the body, the sprung chassis hitting the ground, or binding of the control arms.

2. The Shock.
Droop: This is limited by how far the shaft can come out of the body.
Bump: Limited by how far the shaft can go into the body.

3. The Spring.
Droop: Limited by the free length of the spring.
Bump: The spring will compress until the coils contact each other. AKA Coil Bind.

When you start to put it together the droop or bump limits are determined by the part of the suspension that hits the limit first including the sprung chassis hitting the ground on bump. This happens often with F1 cars.

Where preload can come into the equation is where it positions the shock in the total available travel of the shock. When it is on the car, spring included supporting the vehicle weight it is in its neutral state. When you turn the spring perch toward the spring to raise the car it preloads the spring and makes the shock extend putting it closer to the droop limit of the shock and control arms. It also becomes further from the bump limit, since the limits are determined by the entire assembly. The only thing to watch for is coil bind on the spring because it is being compressed. Coil bind limits bump.

If you turn the spring perch away from the spring it lowers the car. This puts the shock shaft further into the body because it cannot support the weight of the car; the car will sag until the spring supports it, putting the entire assembly closer to the bump limit but further from the droop limit. The spring does not affect this since it is not connected at the ends.

Moving the shock mounting point does not change the position of the shock or spring as an assembly, therefore not putting the assembly closer to either limit. It does however put the wheel and control arms closer to a limit depending on the direction of adjustment

When setting the height of the sprung chassis via the shock mount the spring perch works slightly differently. Assuming the chassis height is set and corrected to the same height with each spring perch change by the shock mount. Adding preload to the spring will lengthen the shock shaft putting it closer to the droop limit of the shock. The catch is the spring is closer to coil bind because of the compression, potentially bringing the shock and spring assembly closer to the bump limit. Removing preload does just the opposite with the exception of changing the spring. The shock assembly is closer to the bump limit with the droop limit being unaffected. However the spring is more likely to free float at full droop.

That was a ton of stuff but hopefully helpful.

Saboteur,

You are correct about the sway bar. In roll it will always keep tension on the spring until you roll the car over. On pitch you would have to begin to wheelie or endo to pull the springs free. Jumping the car will cause them to come free. AKA Rally. The big concern is jacking the car up. Make sure things are settled correctly after lowering.

We are on the same page. Problem is, all the shitty companies that sell shitty "knockoff" coilover setups perpetuate a myth and we have threads like this.

I've been waiting for someone to chime in and say preload creates a harsh ride...

4.5" of preload would!

I think they suggest that setup because the general public always wants a bolt-on optimized setup and would rather not want to figure out how much bump travel they have, etc.

Zero preload is not optimal. In most cases it'll ride like dick due to the compromised bump travel. They suggest it because they are in the ricer business and care about users going low.

My point is that's what the market demands and does not care about proper setup.

Supply the demand, and that's what probably what the general public demands. Lol. I have a ricer side in me with the car at 3.5" pinch, as low as my spring rate and tire compound will allow before the tire will barely scrub the fender before bottoming the shock. My front shocks never hit the stops. With a ~11/16" rake, am letting the shock hit the stop only on the worst bumps on the streets. Negative preload, or whatever you want to call it, my front springs are loose by 15mm, rears at 30mm, meaning I'm losing 15mm FR/30mm RR potential bump travel at the shock.

I guess a more appropriate title should have been "How important is spring captivity?" :)