Spring setup question (longer or shorter spring needed?)

Guys, I'm going nuts trying to figure this out, hoping someone here can shed some clarity.

I'm currently running a QA1 shock in the rear with a 8" 500lb spring. When the car is seated at the ride height I want, the shock is compressed an appropriate amount in its travel range. This shock only allows ride height adjustment via spring perch, there is no secondary height adjustment.

When I jack the rear of the car up, the spring comes unseated by about 1/4". ie, "negative preload". I'm guessing it's pretty unlikely for the rear wheels to come off the ground in street driving, but it's possible in racing and this might result in a loss of control. Therefore I'd like to maintain my ride height but have a bit of preload on the spring.

Do I need a shorter spring or a longer spring? What's messing me up is the lack of preload.

I could also think of this problem as if I added in the appropriate preload, it would end up raising the car by about 1/2". In that case, since I want to go lower from there (back down 1/2"), I'd need a shorter spring, right? Or would the shorter spring result in even more negative preload?

I know helper springs exist, but is it possible to solve this problem with longer or shorter main springs?

Appreciate any help!

Mike Pass

You do not say where the spring perches are placed in relation to the available thread on the damper. However assuming there is sufficient thread available you need a longer spring of the same stiffness. This longer length will allow the spring to remain in contact with the spring perch at full droop. Because this spring will be longer the spring perches will be in different position so that the spring compression will still need to exactly balance the weight of the car at the normal ride height. A 1" longer spring of the same stiffness should work OK.

Terry Oxandale

Skinny Man
Mike, Please help me understand this fix. If Brian goes to a 1" longer spring with the same rate, 1) the car would sit higher if the perch was not adjusted down by the same 1"...problem still exists because all that was done was move the spring down the same amount that the spring was lengthened, or 2) Brian could compress the spring slightly (preload) by 1/4" as noted, but then the car would compress the spring a lesser amount due to the preload, so he'd have a higher sitting car again, or 3) Brian could obtain another spring (longer or shorter), but of a lower spring rate so that the spring could be lightly preloaded by the 1/4", and then the lower rate would allow the car to compress the spring more, but still be in the middle of the shock range, or 4) insert a helper-spring, which has negligible spring rate, but will place a slight compression on the main spring at all times. This way, he could keep his current springs, but just move the spring down a half inch or so to allow for the helper spring's compressed thickness.

Part of my logic is that I'm guessing his car is only compressing the springs maybe 1.25" to 1.50" with this heavy a spring rate (again, I don't know the geometry), and if the spring currently has 1/4" slack in it, isn't that when the shock hits the limits? If so, then preloading a same length or even a longer spring would unload the suspension sooner (abruptly in option 2), which could be a potential problem? Yes, every manufactured car you buy from a dealer has pre-loaded springs, but these cars all have a great deal of shock movement, and relatively weak spring rates, which pretty much prevents any full shock extension in anything but a most extreme situation. I believe in this case with Brian, he could put any length of 500 lb spring in the car (longer or shorter), and would have the same problem unless he goes with a shorter shock, or a lower spring rate (or a helper spring) to keep the shock lightly preloaded at all times.

I hope I made since in my query or confusion, but this is an issue I have as well, and 8 years of occasional track time has never caused the suspension to droop so far as to unload the spring. I suppose that could happen, IF the shock was completely blown out, and the spring rate was so high that any amount of droop would unload the wheel, but you'd probably have a lot more problems to worry about at that point. My guess is that at that spring rate (500), that the QA1 shock will need some stiffness in it anyway to provide a good ride. BTW, this is the same shock and spring rate I am using on my project. The large selection of shock lengths provides the user the appropriate length for the expected spring rate/corner weight compression. Typically the longer the shock travel implies a lower spring rate to keep it all connected, and that's were the helper springs help out for adjustments to a less-than-ideal shock travel range.
Last edited:

Joel K

To Terry’s point here are some pics of using helper springs with your existing springs and shocks. They fully collapse when car is at ride height and only expand when the suspension goes to full droop to keep the springs seated on their perches.

Here are two pics from Cam T’s SLC build…25 lb helper springs…
At full droop…

at ride heigh…the helper spring is fully compresse…
Terry, thanks for your detailed thoughts there. Joel, can you tell me what spring spacers you are using? Are you using Hyperco helpers? (due to the dark blue).

Thinking through this in steps, here's what I'm thinking (assuming a 1:1 motion ratio and zero preload to keep it easy):

Option 1): Use a 1" longer spring, lower perch exactly 1". Car will sit at the same ride height and still have the negative preload (same rate, and same relative position of spring and shock length). Take up preload (1/4"), now car will sit 1/4" higher than originally. Same net effect as if I had taken up preload on the spring on there now.

Option 2): Use a 1" shorter spring, raise perch exactly 1". Car will again sit at the same height with the same negative preload. Take up the preload, and now the car will sit 1/4" higher than before.

So in both cases, it appears there is no change in ride height or ride quality since we're using the same rate spring, only to the position of the perches on the shock body. This leads me to the conclusion that changing spring length, while keeping the same rate, is only useful when you run out of threads one way or the other. It repositions your perches on the body with zero impact elsewhere.

Therefore, if I want to keep the same rate, it seems my only option is the helper springs. Any contradictory thoughts?

By the way, my car's geometry is indeed a bit limiting. The mechanical limits of travel are quite low, about 4" at the shock mounts. We chose the closest QA1 available, and in fact when the car is sitting it's right in the recommended compression provided by QA1.
Joel: do I also spy the stanceparts lift cups there? How do you like them? I am tempted to get a set but only have 1" droop available on my front shocks. It may be OK though as due to the motion ratio, its about 1.75" at the wheel.

Joel K


I have the same setup as Cam‘s, but I’m still in build phase. The lift system is the Ramliftpro which is hydraulic and requires a shorter spring. The StanceParts is air driven and allows for a longer spring. Each system has it’s benefit, but most new builds seem to be choosing Stanceparts.

Here are the parts numbers..

HYPERCO 2.5” ID x 4” Long 25 lb Blue Take Up Spring - P/N CS100
Helper Spring Guide: Genesis technologies 2.5” guide - P/N G1160
Id say, longer spring (so it sits in the cups) less lb to create preload.
Id say, longer springs(so it sits in the cups) same lb to correct your unseated issue..
Basically if your car sits on ride height and it doesn't drop, there's little to no preload (as preferred in a GT40).
Usually you wind up the perches to create preload to achieve something. Usually dragracers like preload on the front springs so it comes out of the springs easy when the hit the throttle distributing the weight of the car to the rear axle creating more grip.

Have you calculated your spring setup? as 500lb might be to heavy.. There are lots of calculators out on the web.

Interesting book, taught me al lot about preload and setting it.

Chris Kouba

To Terry’s point here are some pics of using helper springs with your existing springs and shocks. They fully collapse when car is at ride height and only expand when the suspension goes to full droop to keep the springs seated on their perches.


This is SOP for rally and off road racers. In my mind it's the proper way to do it for all the reasons being documented.
As everyone else said, use a tender spring, this is a standard thing for us rally guys - don't be tempted to run it, your suspension goes to completely unloaded more than you'd imagine even on the road.
If you want to be really fancy you can use lockrings and secondary springs to set the point they transition:


But I don't think you need to go that far.
Last edited: