How does preload affect ride quality?

[Boulderguy]

For example - a coilover system has 50mm of sag at any corner. Would there be any difference in ride quality between 10mm of preload & 30mm of preload?

 

Seems to me that in theory ride quality wouldn't be affected until preload met or exceeded sag. Is that correct? (Obviously that wouldn't work in reality, working in a vacuum here.)

 

There's another school of thought that any increase in preload will increase the amount of force necessary to further compress the spring, thereby dramatically affecting ride quality. That doesn't sound accurate to me.

 

Thoughts?

[Boulderguy]

And when I say ride quality I mean sensitivity to bumps basically.

[SubiGT]

in for replies

 

curious about this too, especially since I'm gonna $$ for corner balancing in the spring.

[biz77]

On a non-progressive rate spring, shouldn't rate and therefore ride quality be unaffected? What are you finding BG?

[Yamarocket630]

With constant-rate springs, about the only difference will be that less preload will give you a more consistant spring effect from full top out to full bottom out, as not even a constant-rate spring is truely constant-rate. All compression springs are progressive rate to some degree. A large amount of preload can also cause coil bind at extreme compression, but unless your springs are far too weak (and require a lot of preload) or too short that should not be an issue.

 

A properly rated spring shouldn't have a large effect on ride quality, the springs only real jobs are to support the cars static weight and to extend the shocks after they are compressed by a bump. The shocks damping valves should do the rest.

 

Your best bet IMHO is to buy springs of a rate that will allow you to acheive desired ride height with your ride height adjustment in the middle of the useable range and with just enough preload to keep the spring compressed lightly at full top out.

[Boulderguy]

^^ does that mean no, the preload won't affect the bump sensitivity in this scenario?

 

I'm not finding anything yet Biz, just trying to understand the physics of it all & hopefully avoid some trial & error.

[Yamarocket630]

With properly rated springs, preload has VERY LITTLE affect on ride quality.

[Boulderguy]

Thanks, that's what I needed to hear.

[easy19]

not an expert, but from what i understand, more preload will affect when the spring will begin to work. if a spring is rated for 10 lbs/cm, and you have 1 cm of preload. it will take 10 lbs of force to start the spring moving. therefore if you have 3 cm of preload it will take 30 lbs of force to begin that same spring moving. numbers are random but theory is sound. in your example, you will lose some of the sag, and thus increase ride height (assuming you dont have seperate ride hieght adjustment). also making initial bump response a bit more harsh. i cannot specifically speak as to what level of difference this will make, but it will make a difference.

[SubiGT]

Your best bet IMHO is to buy springs of a rate that will allow you to acheive desired ride height with your ride height adjustment in the middle of the useable range and with just enough preload to keep the spring compressed lightly at full top out.

So, with my coilovers off of the car, I should set the spring perch to fully extend the shock, then give it a couple of notches of compression? That would give me light compression at full top out. Then I can spin the unit in the strut mount to set ride height.

 

I can't wait to get a garage again!!!

[Boulderguy]

Actually my theory is this - your 10lb/inch spring compressed (preloaded) 3 inches will require a force acting upon it greater than 30 lbs before any movement will occur, correct. But now add 50lbs (5") of car on top of it. It's now "preloaded" from the vehicle with 50lbs of force, thus negating the initial perch preload. So my theory is that preload has no effect until it surpasses sag, since the spring will be "preloaded" with the sag.

 

there are others that say (incorrectly I believe) that the 30lbs of preload will compound the 50lbs of vehicle compression & result in an effective preload of 80lbs. That's basically where your theory is headed.

[jamal]

the big thing preload does is alter where the car sits in the range of suspension travel. More preload means less droop travel and more bump.

[SubiGT]

Actually my theory is this - your 10lb/inch spring compressed (preloaded) 3 inches will require a force acting upon it greater than 30 lbs before any movement will occur, correct. But now add 50lbs (5") of car on top of it. It's now "preloaded" from the vehicle with 50lbs of force, thus negating the initial perch preload. So my theory is that preload has no effect until it surpasses sag, since the spring will be "preloaded" with the sag.

 

there are others that say (incorrectly I believe) that the 30lbs of preload will compound the 50lbs of vehicle compression & result in an effective preload of 80lbs. That's basically where your theory is headed.

If you look at your example, you've compressed 3 from the bottom(preload), and 5 from the top(real load). The spring is still seeing 8 units of load, no matter where they are coming from. That 3 is always there.

 

This actually makes a lot of sense to me now. I have 6kg/mm springs on my Teins. When I noobily installed them, I now know I used preload to set ride height to a certain degree. This has changed the ride quality of a relatively soft spring to be relatively harsh. I can't wait to rediscover the suspension once I do it right.

[Boulderguy]

If you look at your example, you've compressed 3 from the bottom(preload), and 5 from the top(real load). The spring is still seeing 8 units of load, no matter where they are coming from. That 3 is always there.

 

Not to criticize your spring choice but I think most would argue that the Tiens are harsh to begin with.

 

In that example the spring is seeing 2 units of compression from the top (car's weight) & 3 from the bottom (perch preload), creating a spring under 50# of tension total. The perch preload will limit the sag but does not ultimately change the tension total. The total is still only 50#.

 

Here's another way to look at it - with no perch preload the car will compress it 5" with 50#. Once the car is resting on the spring if you were to add 3" of preload you would simply raise the car's weight 3". The spring would still have the same compression & be under the same 50# of tension.

[SubiGT]

Well, either way, I loaded my springs too much during initial setup. I have the 6kg/mm, the USDM ones come with 8kg/mm front and 9 kg/mm rear. That's gotta be really harsh.

[Boulderguy]

I can't imagine 8/9, that would be brutal. The Megan springs are 6/8 & I feel every crack in the road. Just ordered Swift replacements that are 4/6, will see how those do. The Swift lowering spring kit (IE the ones that use stock shocks) are 4.3/6.6 and are considerably stiffer than stock.

[jamal]

I can't imagine 8/9, that would be brutal. The Megan springs are 6/8 & I feel every crack in the road. Just ordered Swift replacements that are 4/6, will see how those do. The Swift lowering spring kit (IE the ones that use stock shocks) are 4.3/6.6 and are considerably stiffer than stock.

 

that's mostly because you have megan shocks and about 3" of total travel. Our car with 8/9k springs on KW clubsports actually has a pretty good ride.

[easy19]

Actually my theory is this - your 10lb/inch spring compressed (preloaded) 3 inches will require a force acting upon it greater than 30 lbs before any movement will occur, correct. But now add 50lbs (5") of car on top of it. It's now "preloaded" from the vehicle with 50lbs of force, thus negating the initial perch preload. So my theory is that preload has no effect until it surpasses sag, since the spring will be "preloaded" with the sag.

 

 

there are others that say (incorrectly I believe) that the 30lbs of preload will compound the 50lbs of vehicle compression & result in an effective preload of 80lbs. That's basically where your theory is headed.

 

if you had 10lb/inch springs with 1 inch of preload and a 50 lbs of force from the car, the car would sag 4". if you had 10lb/in springs with 3 inches of preload the 50 lbs of force, the car would sag only 2" and you have comprimised ride height and added some harshness to the ride as the spring is loaded deeper into its cycle.

 

 

if you have 30lbs of preload with a 50 pound car you do not have 80lbs of preload, you still only have 30lbs of preload as the 50 lb car still provides more force than the 30lbs of resistance the springs are providing. you are just forcing your suspension to ride higher in the stroke, and have less up stroke and more harsh ride.

 

i think that we are getting beyond my expertise level and you may want to check with some of the susp pros, but the basics are that, if you set ride height with preload you are comprimising travel, sag and ride.

 

the springs only support weight, valves in shocks and struts then control compression and rebound. ride height is set with a seperate ride hieght adjustment. for any give spring with any given car there should be a pretty specific preload that those springs were desinged to operate with.

[LittleBlueGT]

This drives me crazy.

 

There are no spring/coil-overs for our cars where the pre-load will be more then the cars force on that spring. Pushing up on the spring, pushing down, how does the spring know?

 

If you put 1 inch more pre-load in the spring, the car will be 1 inch higher.

 

I think the whole wording of "pre-loading" confuses people. Once the spring is compressed more then it was pre-loaded, the pre-loading doesn't come into play (in a static environment).

 

Will it affect ride-quality? Absolutely!

 

Ideally you would want about the same amount of suspension droop and suspension compression. (I am no expert at the exact way our car should be set-up, but the following is all following the laws of physics, period) The following is example is over-simplified just to show the differnce it can make in one instance.

 

So let's say the suspension has 4 inches of total travel:

 

-2 inches of comp (then the suspension hit the bump stop, not coil-bind)

-2 inches of droop (physical limit of dampers, or control arms, spring still has some pre-load on it)

 

If you pre-load the above example with an extra inch, then you would end up with:

 

-3 inches of comp (assuming the suspension still hitting the bump stop, and coil-bind was still not an issue)

-1 inch of droop (physical limit of dampers, or control arms, spring still has some pre-load on it)

 

Now you can go over bumps that push the wheel up 2.5 inches, and not hit the bump stops, or physical limits of the suspension, which may be good. But it is much easier for the car to lift a wheel around a corner, or for a tire to lose contact with the ground in some situations.

 

Now let's reverse it (which is what most lowering spring do):

 

Next post............

[Boulderguy]

Good points, all of them. In order to preserve apples to apples, let's assume that the road surface has a 1" bump or lip, like this -

 

 

_____-----______ (imagine that's 1 inch vertical & somewhat rounded on the edges)

 

 

Let's also assume we're not approaching coil bind, bump-stops or limits of travel. None of those were the issue at hand.

 

So the question is simple, does preload affect how that bump will feel to the driver, all other factors notwithstanding?

[Boulderguy]

if you had 10lb/in springs with 3 inches of preload the 50 lbs of force, the car would sag only 2" and you have comprimised ride height and added some harshness to the ride as the spring is loaded deeper into its cycle.

 

With the same 5" spring loading in either case, how is the spring loaded any differently?

 

 

 

you are just forcing your suspension to ride higher in the stroke, and have less up stroke and more harsh ride.

 

I think it's generally accepted that harsh ride is a result of poor bump compliance, meaning the spring/strut's ability to compress when encountering a bump. Less compliance will jolt the driver/vehicle upwards (which hurts). Less extension will simply create a feeling of "getting air" as you drop off the bump. Not ideal, granted, but not harsh either.

[LittleBlueGT]

Good points, all of them. In order to preserve apples to apples, let's assume that the road surface has a 1" bump or lip, like this -

 

 

_____-----______ (imagine that's 1 inch vertical & somewhat rounded on the edges)

 

As long as the damper was within its intended range it would make no difference.

[LittleBlueGT]

if you had 10lb/inch springs with 1 inch of preload and a 50 lbs of force from the car, the car would sag 4". if you had 10lb/in springs with 3 inches of preload the 50 lbs of force, the car would sag only 2" and you have comprimised ride height and added some harshness to the ride as the spring is loaded deeper into its cycle.

 

The spring does not get loaded deeper into its cycle!!!!!!!!!!!

 

OK!!!!!!!!!!!!!!!

 

If you have like (3500 car, so app 900 lbs of pre-load per corner) 1000 lbs of pre-load, then you would be right.

 

That is not ever going to happen!

 

Some people like to over complicate physics.

[LittleBlueGT]

Next scenario, which is actually very very common on a strut based suspension. And becomes a huge problem for probably 75% of lowered cars, if not more! Yes it really is that bad, if not worse!

 

 

Scenario #2:

 

So let's say the suspension has 4 inches of total travel:

 

-2 inches of comp (then the suspension hit the bump stop, not coil-bind)

-2 inches of droop (physical limit of dampers, or control arms, spring still has some pre-load on it)

 

If you pre-load the above example with one less inch, then you would end up with:

 

-1 inch of comp (assuming the suspension still hitting the bump stop, and coil-bind was still not an issue)

-3 inches of droop (physical limit of dampers, or control arms, spring still has some pre-load on it)

 

Now you can go over bumps that try to push the wheel up 1.5 inches but the car will hit the bump stops first.

 

THIS IS WHAT IS HAPPENING IN OUR LGT'S WITH 90% OF THE LOWERING SPRINGS THAT WE HAVE! Some are worse then others. I can almost gaurantee that it happens on all Tein equipped cars.

 

Most lowered cars that use anything based on the OEM system (stock dampers, KYB, Tokico) are not set-up right. They have very little compression range.

 

This can be much lessened with a much stiffer spring (and of course dampers to match). If the spring is much stiffer then it will take a lot more force to hit the bump stops, but it hasn't changed the fact that the car only has 1 inch of available suspension compression in the front.

 

 

 

Now a thread about pre-load is likely biased towards coil-overs. A few things to keep in mind: the damper is designed to have the piston in a certain range of the stroke. That is why a coil-over with separate pre-load and ride-height adjustments is perfect, as this allows the car to be set-up in such a way that the damper is within its ideal range of motion, and the car has sufficient amount of droop and comp range of motion.

 

A coil-over that doesn't have both adjustments, is it worse?

 

Maybe, but not necessarily. If the car's ride height is set-up such that it is within the ideal range of motion, it would be just right. But that wold not be adjustable like a more expensive coil-over. Most coil-over manufacturers will specify a certain range of ride height that the coil-over works best in, stay within those parameter, and you should be fine.

 

To answer your question more exactly.

 

In many situations the pre-load adjustment will not affect ride-quality, it does not make the spring any stiffer, or make it magically have more load on it.

 

It can in practicality affect ride quality, because range of motion (specifically compression) is a much bigger factor then many think. Imagine you are going around a corner (so outside springs are compressed) and then you hit a bump mid-corner...........Very easy for many many lowered cars to touch the bump-stops, thus affecting ride-quality and reducing grip.

 

Hope that helps.

[NSFW]

I don't own coilovers, but it seems to me from looking at them that the preload adjustment works exactly like the ride height adjustment, but at the other end of the spring. If you adjust the ride height ring 5mm and adjust the preload ring 5mm, the only thing that changes is the position of the middle of the spring relative to the shock body. If you adjust only one of them (either one) the ride height will change - the only thing different about adjusting one vs. the other is the position of the middle of the spring relative to the shock body.

 

If I'm wrong about this I'd love to know why because I can't see how it could possibly work any other way.