Subaru Legacy Forums

Subaru Legacy Forums (http://legacygt.com/forums/index.php)
-   Suspension/Brakes (http://legacygt.com/forums/forumdisplay.php?f=20)
-   -   Is it bad to mess with a coil's spring preload? (http://legacygt.com/forums/showthread.php?t=189675)

Buzzman 07-19-2012 07:36 AM

Is it bad to mess with a coil's spring preload?
 
I'm brand new to coilovers and in attempt to fit my wheels I'm going to adjust the ride height. However, I wasn't sure if adjusting the preload would have any benefit? Or am I not suppose to mess with the setting at all?

Thanks.

sheppo9 07-19-2012 06:26 PM

If the spring is loose - i.e not pre-loaded (i.e the car is dumped) you loose travel, which equals a rougher ride.

Can you wind the strut insert up and down or is it just the spring that can be changed?

Dujo 07-19-2012 09:00 PM

Preload is one of those adjustable factors, so you can adjust it; the question is: do you want to? Coilovers are generally made with pretty close to the right spring rate for the dampers without any significant additional preload. You can add more if you want to firm up the handling (and the ride at the same time).

The way they are usually set up from the factory and the way that I've read most folks here recommend that they be set up is to loosen the collar until you can move the spring up and down just a bit, then crank it back down a few turns. You should still be able to rotate the spring by hand, but there should be no up and down or free loose motion by the spring. (If your suspension is very noisy when driving, you're still a little too loose.)

This is essentially, no preload or minimum preload. This is at least where you should start with your coilover setup. If you still want a firmer ride and handling response, then add some additional preload. Note that as little as 5mm or less in spring preload compression is a *significant* increase in overall suspension stiffness. If you adjust preload, you will only need to do it a few collar turns/mm at a time.

In terms of preload adjustment affecting actual ride height, there is some minimal effect on ride height by making the springs stiffer before the weight of the car is resting on them ... the car won't far as fall once sitting back on the suspension since you've effectively increased the spring rate by adding preload, but it is relatively minimal compared to the actual ride-height adjustment. You really want to set the ride height by determining how far up the lower suspension mount is threaded on to the center threaded strut section.

This is of course extremely easy to change before the coilovers are mounted on the car. It's a little harder once they are installed. You gotta think about which collars are turning which way to get the center threaded part to spin the right way to go up or down as you want since the lower strut mount is fixed in place (rotationally anyway) once the lower strut bolt is installed. Still beats pulling the lower strut bolt and reinstalling it just to change ride height.

Enjoy!

scoobyscoodle 07-19-2012 09:08 PM

What type of coilovers do you have?

scoobyscoodle 07-19-2012 09:13 PM

Quote:

Originally Posted by Dujo (Post 3989216)
In terms of preload adjustment affecting actual ride height, there is some minimal effect on ride height by making the springs stiffer before the weight of the car is resting on them, the car won't far as fall since you've effectively increased the spring rate, but it is relatively minimal compared to the actual ride-height adjustment. You really want to set the ride height by determining how far up the lower suspension mount is threaded on to the center threaded strut section.

Preload will absolutely effect ride height, how do you think KW/RCE's work?

Preload does not have any effect on spring rate. Preload is simply stored energy. A 400lb spring with 1" of preload still has an effective rate of 400lb.

Dujo 07-19-2012 09:42 PM

^ Please note my signature below.

That said, my understanding about spring rate is that spring rate is essentially a measure of how much weight is required to compress a spring a certain amount. If a spring is already compressed some, doesn't it make it harder to compress it more?

I freely admit my limited understanding of all things car related though. Feel free to expand on what you're saying.

How do KW/RCE's work. I have no idea.

scoobyscoodle 07-19-2012 10:29 PM

Quote:

Originally Posted by Dujo (Post 3989280)
That said, my understanding about spring rate is that spring rate is essentially a measure of how much weight is required to compress a spring a certain amount. If a spring is already compressed some, doesn't it make it harder to compress it more?

I freely admit my limited understanding of all things car related though. Feel free to expand on what you're saying.

How do KW/RCE's work. I have no idea.

If the spring is a progressive rate, then yes, putting preload on it would essentially increase the rate since you are compressing it to the point that the rate increases. Most coilover springs are linear, so the rate is the same through the entire travel range. A 400lb linear spring has a 400lb/in rate uncompressed, compressed 1", or compressed 3", it does not matter; the spring will always take another 400lb of force to compress an additional inch.

Preload is just stored energy in the spring. If the stored energy in the spring from preloading added up to the weight of the vehicle or more, the springs would not compress at all when dropped on the ground.

RCE/KW's adjust height by adjusting preload only. They do not have a separate height adjustment like BC/ISC etc. etc.

jamal 07-20-2012 12:38 AM

Preload changes the bump to droop ratio. If you are banging off the bumpstops for example, more preload will give you more bump travel but less droop. To actually have a signficiant effect on spring rate you would need more preload than there is weight on that corner (which would also mean zero droop and that the suspension wouldn't compress at all when you set the car down).

Dujo 07-24-2012 08:12 AM

Quote:

Originally Posted by scoobyscoodle (Post 3989341)
If the spring is a progressive rate, then yes, putting preload on it would essentially increase the rate since you are compressing it to the point that the rate increases. Most coilover springs are linear, so the rate is the same through the entire travel range. A 400lb linear spring has a 400lb/in rate uncompressed, compressed 1", or compressed 3", it does not matter; the spring will always take another 400lb of force to compress an additional inch.

Preload is just stored energy in the spring. If the stored energy in the spring from preloading added up to the weight of the vehicle or more, the springs would not compress at all when dropped on the ground.

RCE/KW's adjust height by adjusting preload only. They do not have a separate height adjustment like BC/ISC etc. etc.

This doesn't quite make sense to me. If we're talking about a linear rate spring and you are saying that another 400 lbs will compress the spring the an additional inch (until full spring compression anyway), then how does preload affect ride height?

Do you see what I'm saying here? The sprung weight of the car does not change in this scenario. If you are saying that the amount of preload already on the (linear rate) spring does not affect the amount of spring compression (still always 1" / 400 lbs in our example), then the car, should fall the same distance when set back down on the suspension, right?

I'm confused. Please clarify if able. I swear I'm not trolling on this issue, I'm just trying to reconcile my understanding. Thanks!

scoobyscoodle 07-24-2012 12:45 PM

Set the car down on the ground with zero preload (hardly snug spring retainers). The car will compress x amount from full droop, which depends on the spring rate and weight of the vehicle. Now assume: 1. We have 400lb/in springs, 2. We have a 1600lb car, 3. The car has a perfect 50/50 f/r and r/l weight distribution.

Now put 1" of preload on all 4 corners, and there will be zero compression when you drop the vehicle on the ground, the static and full droop heights will be the same in terms of hub to fender measurements.

So in this example assume in the first case with zero preload, you had 3" of compression between full droop and static. That would mean you could raise the static height of the car up to 3" (not that you would ever do this) because at that point there would be no more droop travel left.

Typically you adjust preload to change the bump/droop travel distribution, as you want roughly equal amounts of both. The KW/RCE's are not meant to have a huge range of adjustable height's, they are designed for the BP/BL chassis specifically, and those acceptable ride heights. But with KW/RCE's preload does adjust your ride height within a certain range.

jamal 07-24-2012 02:48 PM

With KW/RCEs you have a helper, which gives you a pretty wide range of height adjustment without preloading the main spring.

scoobyscoodle 07-25-2012 02:31 AM

^Ah yes, that too.

Buzzman 07-27-2012 12:27 PM

Well I inadvertently messed with the spring's preload prior to reading this thread and it seems I messed something up...whenever I travel over even the slightest bump, my front passenger wheel makes a weird thumping sound. I took the wheel off and it seems the plastic cover that sits under the spring is crooked? Anyone know how to fix this?

Dujo 07-31-2012 07:16 PM

^ I'm not quite sure what you mean here. Pics?

sheppo9 07-31-2012 09:27 PM

The dust boot?


All times are GMT -6. The time now is 01:21 AM.


LegacyGT.com