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?" :)