Spring preload?

[bozothenutter]

I don't get it.......
Why do people keep saying it increases spring rate?
The spring rate is a given, it doesn't change!
Spring rate:
If you put weight X on the spring, it will compress X mm
Spring preload:
If you put weight 'X' on the spring and leave it there, it will compress 'X' mm and stay that way until the spring is removed.
If you want to move the spring another 'X' mm, you add another 'X' amount on top of what is already there.
Unless the spring is pro-, or digressive, preload has no impact on the spring rate.

Or am I'm missing something here?

 

[Steven103]

You are completely correct. It’s an entirely misunderstood concept, widely quoted on many forums.

 

[JamesBryan]

On linear rate springs (which most are) you are right.

It would alter on a progressive rate spring though.

 

[bozothenutter]

On linear rate springs (which most are) you are right.

It would alter on a progressive rate spring though.

See the third from last line.....😉

 

[JamesBryan]

See the third from last line.....😉

Missed that bit 😅

 

[Steven103]

Linear springs:

• More preload: ride height increases, available rebound travel decreases, high speed compression damping decreases and/or rebound cavitation occurs earlier (i.e. occurs over less severe bumps and at less extreme temperatures).
• Less preload: ride height decreases, available bump travel decreases, spring aid is contacted earlier which gives a more sudden and more dramatic change in under/oversteer balance, high speed damping performance increases/cavitation occurs later, damper internals run at a higher pressure so oil seals potentially fail earlier, damper gas force increases so the effective spring rate at wheel increases slightly.
• Too much preload: literally run out of rebound travel & get knocking noises, less overall grip if wheel is being picked up off of the ground.
• No preload: spring becomes loose in rebound and rattles, spring rate is effectively zero during some of the suspension's travel.

That's all I can think of. Nothing about spring rate or load in the spring in any of the "normal" examples.

I think the reason why people assume that preload does something more meaningful is that they are always looking at a coilover in it's natural fully extended length either on a bench or with a car on axle stands. Because the damper can't possibly extended any more, moving the adjuster does add load to the spring.

But as soon as you put the car on the ground the damper returns to a middle ish position. Now when you move the adjuster up you are not adding load to the spring because the damper is free to extend to compensate, you are simply moving the spring up and hence the ride height increases. The total amount that the spring is compressed does not change because the weight of the car does not change.


Progressive springs:

• Irrelevant. All of the popular 1*2 coilover kits have linear springs anyway.