Spring Pre-load

[VSPEC32]

Getting close to putting my car on the road and I need to move the spring landing on my coilovers to give me a little more clearance on the rim. This will obviously change the spring pre-load, but I'm not sure what that means. Anyone care to explain to me what the affects of more or less pre-load will mean.

Cheers

Brendan

[salad]

Your car will be raised up by moving the lower spring seat.

Preload is how much the load is applied to the spring before you put the weight of the car onto it. You need an incredible amount of preload to start effecting the linearness of the spring once the weight of the car is on the spring, so I wouldn't worry about it.

[R.C]

Getting close to putting my car on the road and I need to move the spring landing on my coilovers to give me a little more clearance on the rim. This will obviously change the spring pre-load, but I'm not sure what that means. Anyone care to explain to me what the affects of more or less pre-load will mean.

Cheers

Brendan

Pre load is used to adjust static weight distribution. With linear rate springs, force is proportional to displacement, ie F = kx. The more displacement of the spring the higher the spring force, so if you increase the preload (ie wind the spring seat up) you will increase the force on that corner of the car and therefore shift the weight onto the other corners accordingly.

The only way to properly set the car up is with a flat patch and scales on all 4 corners of the car, you can approximate by adjusting the spring seats to the same length but this will never be right because the car wont have exact 50/50 weight distribution front/rear and left/right and also the spring rates will never match exactly.

Increasing preload will also change the ride height though, that is why good coil overs have separate height and preload adjustment, but usually this is a waste of time on road cars.

Hope that helps.

[salad]

It's true that adding preload will add a force upwards, but dont forget, once the weight of the car is on the spring, all of this force is negated, and you end up all preload gone and the only thing compressing the spring is the car now.

Preload adjustment is mainly for height adjustment. As far as I'm aware, preload has no real function as it is all taken up by the weight of the car. You will also notice that in some rear struts, helper springs are used which means you have pretty much no preload at all as the helper spring compresses before the main spring due to its much softer rate.

Edited January 17, 2007 by salad

[VSPEC32]

Hmmm, I'm listening, but now you're both confusing me. I do intend to set the car up properly with the corner weighting, but the reason for moving the spring seat is clearance. Not sure if 10mm of difference in the pre-load would affect the handling as such, but more the corner weighting...is that basically what you're both trying to say?

Cheers

Brendan

[R.C]

[it's true that adding preload will add a force upwards, but dont forget, once the weight of the car is on the spring, all of this force is negated, and you end up all preload gone and the only thing compressing the spring is the car now.

As far as I'm aware, preload has no real function as it is all taken up by the weight of the car

if you have no preload then with the weight of the car the suspension will be compressed more. Just balancing of forces - if no preload then the resultant force compressing the spring is higher therefore more compression of spring and lower ride height.

Hmmm, I'm listening, but now you're both confusing me. I do intend to set the car up properly with the corner weighting, but the reason for moving the spring seat is clearance. Not sure if 10mm of difference in the pre-load would affect the handling as such, but more the corner weighting...is that basically what you're both trying to say?

thats about right - your handling would only be affected if you have different corner weights and by the increase in COG (increasing your ride height). The preload won't affect how "stiff" your ride is either.

If you coilovers only have single adjustment for spring seat heigh (that is you cant adjust height and preload separately)

1. Set car up to ride height by setting spring seats

2. If you have scales adjust your corner weights by tuning the preload. If not you can just go with getting the height roughly the same, you won't be able to tell the difference much on the road anyway.

[VSPEC32]

I have a set of RG JTC'N1 V Stage coilovers with both spring seat and mount height adjustability.

http://www.sillbeer.com/2005/12/rg-goodness-arrives_14.html

They should be fine then for my needs.

Thanks for the help fella's.

Cheers

Brendan

[salad]

if you have no preload then with the weight of the car the suspension will be compressed more. Just balancing of forces - if no preload then the resultant force compressing the spring is higher therefore more compression of spring and lower ride height.

The spring does compress more without preload, but dont forget that to increase preload, you have to raise the spring seat up. In doing this it raises the car. In single way height adjustable shocks (without helper springs), you add more preload to raise the car up. If they have helper springs, there is bugger all preload force, helper srings are very soft.

[T04GTR]

ohhhhh thats interesting. i thought you had to atlter the height of the strut (body adjustable) to do corner weights properly?

i spose it has the same afect.