Preloading, how to tune it?

It's been a while since I've been interested in the technical side of performance. So here it goes.

Back then spring and height adjustment weren't that common, on a affordable level anyway.
But there have been a few "budget" coilover systems showing up recently, that now have independent height and preload functions.
Usually found on higher end systems.

I've been looking around on the net and searching these forums to find some info. And so far I've learnt a few things but didn't find what I want.
This thread: http://www.ozhonda.com/forum/showthr...hlight=preload
Good thread, it explained things pretty well but maybe I didn't understand it all.
Some things got me confused :confused:
Compressing the spring = preload. And by compressing a spring u also lower ride height/shorten suspension travel, yes? If that's the correct, some of the things I have read seem contradictory to this. :zip:

My question is, with this function now available on many coilovers. How does this translate to tune-ability. Can preloading have any positive affects on handling, taking into consideration types of braces, bars and tyres?

Or is it merely there to keep the spring in?

Further more, does anyone have a setup that'd like to share?
From tyre choice, suspension, etc, etc, to height, camber and toe?
State weight of vehicle too please :D

Having read some of people thoughts, they've come to the conclusion that the preloading function is.....useless :(

Hoping someone here has something more positive to say or maybe point me in the right direction :)

Thank you all and please excuse my engrish.

Preload is the distance a spring is compressed , relative to a uncompressed shock. Its done with the shock static :)
IMO i have simply adjusted "preload" to keep the spring held firmly and no more.

For a street car preloading isnt neccessary at all, set the preload to zero. That means adjusting them so that the spring (while the coilover is off the car and fully extended) is held firmly between the top mount and the adjustable spring pirches, but not firm enough to compress the spring at all. Doing them up by hand is all you need do.

With the type of shock that allows you to adjust the legnth of the unit seperatly to the spring preload, it is best for you to leave the prelad at zero, this is the reason why.

Preloading is a very useful tool to adjust where abouts the shock lies in its stroke when the car is sitting at its static ride height. This determines the maxium amount of negative stroke and positive stroke the shock is capable of.

Say you want to lower your car a heap, doing so with just the adjustable spring pearches will reduce the shocks upward stroke. If the car is bottoming out like this, you will need to adjust the actual length of the shock, by the height collar, this allows you to have more shock travel when lowering, to avoid bottoming the shocks out.

A street car should never be reaching its minium and maximum travel, if it is, the springs are too soft for the application, making the AMOUNT of stroke needed of the shock too small.
(shock may have 10cm of stroke (minimum to maxium) but the car wants to bounce up and down more than 10cm. In this case it will be likely that you will experiance both bottoming and topping of the shock, or very extreme and frequent bottoming or topping).

OR

The shock travel range may also be to low in either bump or droop travel, which can be altered with shocks that have seperate length and spring perches.

In your application, having the preload at zero, and adjusting the length for ride height changes, will allow you to keep the shocks well within the ranges of the shock travel you will need for the application.

A very common misconception with alot of people is that adjusting the ride height by the spring perches, changes the stiffness of the unit. This is incorrect, the spring rate, and damping characteristics of the shock will be exactly the same no matter where the spring perches are located on the body. The only thing effected is shock travel.

If your have coilovers where ride height changes are made by adjusting the spring perches, and those coilovers arnt bottoming out at your chosen ride height, then there would be absolutly no benifits in going to a coilover which allows this extra adjustment of shock length, another common misconception.

If i were to severly lower my car, i would definatly go for a coilover which has seperatly adjustable length due to the adjustability of the availiable shock min and max travel. Bottoming out is extremly damaging to the shock, and in the case of coilovers, expensive! not to mention that bottoming shocks during cornering is a very dangerous situation most likley resulting in snap oversteer or undesteer, depending on which end of the car is bottoming.

Ok so basically it's useless in a tuning sense :(
Except the fact you can just go super duper low?

I know motor bikes use preload but for reasons I don't know.
Maybe I was hoping those reasons could be transfered onto cars when it came to tuning suspension.

Oh well, thanks for the help :D

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Originally Posted by nigs

Ok so basically it's useless in a tuning sense :(
Except the fact you can just go super duper low?

I know motor bikes use preload but for reasons I don't know.
Maybe I was hoping those reasons could be transfered onto cars when it came to tuning suspension.

Oh well, thanks for the help :D

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if you preload too much , you are compressing the spring without static or dynamic load on it. This increases the spring rate and is only relevant to single perch adjustable suspension ( Tein SS for example)
Dual perch adjustable , as said only needs the upper perch adjusted to hold the spring captive. The lower perch is to adjust the height. The static spring rate does not change

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Originally Posted by bennjamin

if you preload too much , you are compressing the spring without static or dynamic load on it. This increases the spring rate and is only relevant to single perch adjustable suspension ( Tein SS for example)

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I dont like to correct you, but this is not true, compressing the spring with preload (with the shock out of the car) will not increase the spring rate at all. It truly is a very very common misconception, it is not the case at all.

Say you have a coilover such as the tein ss, 2 situations, one is set with zero preload, the other is set with 5mm of preload (say the spring is 10kg/mm, and it is compressed 5mm, the shock is pushing up with 50kg of force on the top hat when fully extended)

Say the weight of the car on the shock will be 300kg, both springs will need to compress 30mm to take the weight, however the preoaded spring is already compressed 5mm, when the weight of the car is placed on the spring, it will only compress 25mm from its most extended position (to get to the 30mm), where the spring with 0 preload will compress 30mm.

This means that the shock, at static ride height, will have 30mm of availiable bump travel, whereas the shock preloaded 5mm will have 25mm of availiable bump travel.

Now you say the spring rate will change with preload, but both springs need to compress 30mm to hold up the 300kgs. the preloaded shock does it with 5mm of preload + 25mm of travel, and the shock with no preload does it with 30mm of travel.

So at static ride height, both springs are compressed 30mm from their natural, uncompressed length, add another 50kg to either spring, and they will both compress a further 5mm, the spring rate does not change at all from either situation. Remove 50kg from either spring, they will both extend 5mm.

Ive heard so many people stating that more preload equals a stiffer spring, it seems to be thrown around like common knowledge, but its not the case. I can see why they might be confused, with the preloaded spring in the above example, since its compressed 5mm at the shocks full extended length, that means that putting 50kgs of weight on the spring wont compress the spring shock combo at all (the preload itself is pushing out with 50kgs of force), 60kgs of weight will compress it 1mm, however preload does not effect the actual spring rate at all. 10kg=1mm compression aslong the preload has been overcome, and with the weight of the car it always is (unless the car is set with rediculous amounts of preload, which would be extremly bad handling).

The difference is that, with the preloaded shock, it will reach its maxium length when the weight on that corner of the car is 50kg, where the spring with 0 preload will reach is maximum extended position with 0kg of weight on that corner.

Motorbikes often use preload as you mentioned nigs, they use it to adjust the amount of availiable travel the shock has at static ride height. Im not 100% sure of the reason, but i believe its due to the weights of different riders, ie. a really really light rider on a motorbike will compress the spring/shock alot less that a heavy person, in that case they may need more negative suspension travel, this can be done by altering preload and shock length.

not to stir the pot - any static preload/compression on a spring increases its spring rate ? Lets discuss this is interesting :)

I'm guessing that the actual spring rate will not change (going by muzz's example where 30mm travel = 25mm travel +5mm preload) It will just feel stiffer because the spring only physically travels 25mm (with 5mm preload) instead of 30mm (with 0mm of preload)

This is gonna be a good thread.

I hope to see some useful posts in here. :thumbsup:

Consider a coilover that has to hold the corner of a car up with 300kgs of force, that means, that nomatter where the preload is set, to hold the car up the spring must be pushing up with 300kgs of force on the car.

If the spring rate is 10kg/mm, that means the spring must be compressed 30mm from its natural uncompressed length to provide this force. This is not effected by preload.

Lets consider the preload of 5mm or in other words 50kgs for this spring.
That means that the spring is already compressed 5mm from its natural uncompressed length, before the weight of the car is placed on top of it.

When the weight of the car is placed on the spring that is already compressed 5mm, it will sag another 25mm, to make up the 30mm of compression needed to support the 300kgs.

When the weight is placed on the uncompressed spring, it will compress the 30mm needed to support the 300kgs.

This is where the confusion lies, in both situations 300kgs of weight must be supported, yet with 5mm of preload the spring only compresses what seems like 25mm, while the other spring compresses the whole 30mm.

Same weight giving 2 different deflections would usually mean different spring rates. Not here though. The thing is, 30mm of compression gives the same resistance as 25mm of compression with 5mm of preload, in both situations, the spring is compressed 30mm from its origional uncompressed length.

If 50kg is added to the corner to make 350kgs, both springs will need to compress 35mm from their natural length, to support the weight. The spring with zero preload will compress 35mm, the spring preloaded 5mm will compress 30mm to make the needed 35mm of spring compresion.

In both examples the weight on the corner is increased 50kgs, in both examples, the corner sags another 5mm from the extra weight. This shows that the spring rates are equal between the two. It would be the same if 50kg was removed from the corner, both the springs would extend 5mm.

If weight transfer causes 250kgs to transfer from the inside tire to the outside tire, both the preloaded spring and the non preloaded spring will extend 25mm as they are both compressed at a rate of 1mm/10kgs of force.

At this point, the spring with no preload will still have 5mm of droop travel still available, while the spring preloaded 5mm will be at its droop limit, as it only has 25mm of availiabe travel in droop from the static ride height.

Some may think that when the shock reaches its full droop travel, then the wheel gets lifted off the ground. This is not the case. in the above example, 250kg is transfered from the inside tire to the outside tire. The preloaded shock extends to full droop, however there is still 50kg holding the wheel down as only 250kg has been transfered off the 300kg corner, same as with the shock with no preload.

Basically the only thing that changes is how much travel there is for the shock in both bump and droop. At static ride height, supporting 300kgs, the shock with no preload will have 30mm of availiable droop travel, while the shock preloaded 5mm will have 25mm of droop travel, and 5mm more bump travel than the shock with zero preload.

Hope this all makes sence.

Apparently it just feels "stiffer" because more load/force is required to compress the spring further.

I understand that it maybe best to run 0 preload, so that there is MAXIMUM suspension travel. But what about in the old days where the only way to lower a car on coilovers was to preload the spring?

If I understood everything I have read so far. If you were to preload each spring @ 25mm on a 1000kg car using 10kg/mm springs. When u settle the car down on flat ground, it won't sag at all?

So if we installed the coilover with no preload on a 1000kg car using 10kg/mm spring then it should drop 25mm when sat on flat ground? yes/no?

Ok now here's my theory. For arguements sake lets say the total suspension travel/shaft is 100mm. Preloading it by 25mm won't allow the coilover to extend any further than it already is (75mm). So if the car was lifted off the ground, there would be no suspension movement what so ever....

Granted we then lose 25mm of suspension travel (hope I'm using the right term).

So are there any benefits from having a coilover only extend a certain length in regards to handling?

So was I right?!?!!

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Some may think that when the shock reaches its full droop travel, then the wheel gets lifted off the ground. This is not the case. in the above example, 250kg is transfered from the inside tire to the outside tire. The preloaded shock extends to full droop, however there is still 50kg holding the wheel down as only 250kg has been transfered off the 300kg corner, same as with the shock with no preload.

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T_T I don't understand that part :sadface:

don't forget that theres 50kg's worth of preload there to make up for that extra difference

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Originally Posted by nigs

Apparently it just feels "stiffer" because more load/force is required to compress the spring further, therefore causing suspension travel and in turn uses the shock. :o

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No thats incorrect, its hard to explain. The spring wont feel stiffer at all once the cars weight is on it.

As you place the cars weight on the coilovers, it will compress a shorter distance to get to the static ride height, if the spring is preloaded yes.

But now that the coilover is at static ride height adding or removeing weight will cause the same amount of compression or extension as a un-preloaded spring would. The stiffness dosnt change.

It may help to think of it like this, placing the car on the springs is basically like preloading the springs, if the corner of the car weighs 300kgs, the spring is preloaded 300kgs. Just because the shock shaft wont allow the spring to extend the last 5mm in droop (say its preloaded 5mm) to its complete uncompressed length, dosent mean that it wont compress and extend the same distance with the same change in load.

hope this helps.

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Originally Posted by nigs

If I understood everything I have read so far. If you were to preload each spring @ 25mm on a 1000kg car using 10kg/mm springs. When u settle the car down on flat ground, it won't sag at all?

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thats correct:thumbsup:

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Originally Posted by nigs

So if we installed the coilover with no preload on a 1000kg car using 10kg/mm spring then it should drop 25mm when sat on flat ground? yes/no?

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Exactly

Quote:

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Originally Posted by nigs

Ok now here's my theory. For arguements sake lets say the total suspension travel/shaft is 100mm. Preloading it by 25mm won't allow the coilover to extend any further than it already is (75mm). So if the car was lifted off the ground, there would be no suspension movement what so ever....

Granted we then lose 25mm of suspension travel (hope I'm using the right term).

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Your right here except for one thing. Say you preload the spring 25mm it wont compress at all when the weight of the 250kg corner is placed on it.
This means you have 100mm of bump travel at static ride height, and no droop travel at all, the suspension cant extend.

This is a good example to use to show the spring rate stays the same with preloading. Say you preload the spring with a massive 25mm (250kg of force) as in your example, if you add 10 kg to that preloaded corner it will compress the spring 1mm from static ride height. There is 260kgs of weight on the corner, the spring preload is pushing the car up to the shocks full droop with 250kgs of force, the weight pushing down is 260kgs. This will result in the spring compressing 1mm.

Same with a spring with zero preload, add 10kgs to a corner, the spring will compress a further 1mm from static ride height aswell.

The fact is that the cars weight totally overcomes the preload applied to the spring. Once the cars weight overcomes that the preload the spring pushes up with, it will simply compress at the same spring weight as normal.

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Originally Posted by nigs

So are there any benefits from having a coilover only extend a certain length in regards to handling?

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No, maby with some types of formula cars and such it could be used to advantage, but with our hondas, the ideal would be to have the suspension never reaching the limits of the shocks extension or compression.

Ill post a reply to a question jason asked me (hope you dont mind), i think it would benifit all readers. the questin was reguarding setting up the preload on a fwd honda to be used in motorkhana's, it can also be applied directly to street cars and circuit cars.

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Originally Posted by Muzz

Hey man how are ya.
Just a few quick questions before i can give the best answer:
What spring rate are these coilovers front and rear, and do they offer seperate length and preload adjustments?

Preload only effects handling in two situations, when the shock reaches its maximum bump travel (compressing), and when it reaches its maximum droop travel (extending).

Firstly, what you want is for your car to never experience its maximum bump travel. At this point the coilover cant compress any further, in an instant, the effective spring rate will be infinant. Very bad for handling!

So the first thing you need to make sure of is that your car never reaches its maximum bump travel. Many people check this with zip ties on the shock shaft. You put the zip tie around the shaft, do some hard cornering as you would running in a motorkhana, and see how far the zip tie has been pushed up he shaft. It should not reach the top.
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Now regarding times where the suspension goes into full droop..

Before i start on this bit, i should point out, that grip between the front pair of wheels and rear wheels, depends largly on one variable, how much weight transfer there is between the front pair and rear pair of wheels during cornering.

For example, the best grip possible for the front or rear pairs of wheels occurs when the weight is equal between them. when the weight gets transferred from the inside tire to the outside tire the cornering grip decreases.

With our FWD hondas, to go as fast as possible through corners, we want one thing, to maximise the amount of grip possible in the front wheels, then you balance the rear to give you the best rotation/balance.

We want the minimum weight transfer in the front set of wheels, and then to alter the weight transfer in the rear to balance the setup.

Often by setting the car up in this manner, under extreme cornering conditions, the inside rear tire may lift.

One might think that having a tire lift from the ground is detrimental to cornering power, but the truth is that in our fwd hondas, the cornering power is basically dictated by the grip at the front wheels. Having the rear lift is not a problem at all, neither must the rear wheel be lifting to know your car is setup properly.

The front inside tire will never lift off the ground in hard cornering, the forces just arnt great enough, even with race tyres.
Nor should the front tyres ever be setup to reach full droop. If it does your preload is too high.

So up to this point you want to make sure none of the shocks are bottoming out, and the front shocks aren’t reaching there droop limit.

If this is the case, at zero preload, then leave the preload at zero, you wont gain anything by adjusting the preload.

Id recommend zero preload at the rear, Unless the shocks are bottoming out. If so, add preload, at the same time removing shortening the coilover length via the bottom collar, to keep the overall length of the coilover the same.
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Adding preload from zero, will give your shocks more bump travel, taking it from the droop travel.

Removing preload will give less bump travel, giving you more available droop travel, and lowering the car (unless you change the actual length of the coilover by the bottom collar, to keep the length of the unit the same).

So basically what you should do to get the optimum preload on your Coilovers is, set them at zero as you have. Check to make sure none are bottoming out. Check that the front shocks arnt being extended to their limit in droop (extreamly unlikely unless preload is set really high, ill explain how calculate this when you tell me the spring rates) if so, you leave the Coilovers at zero preload.[/B] You keep them set at zero unless you start bottoming out, or the start reaching full droop, due to other changes made in the suspension system.

Hope this helps buddy, let me know if there’s anything I can clear up for you. Let me know the spring rates you have and ill do some calculations for you.

Muzz (lol, had to shorten the post it was over the 5000 character limit, ill talk more about it in that preload thread)

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Do you know what makes all this really hard???

The fact that our cars aren't perfectly balanced. *bangs head on wall*

How do they go about adjusting corner weights? Do they adjust the preload or the height at the base of the coilover?

J

Also: Thats cool for sharing that info from that PM. You went to alot of effort to write it so its all yours man. :thumbsup:

Finally!
Maybe the answer I was looking for.
Preload will give more bump travel but less droop?
And vice versa?

But wouldn't preloading, shorten the overall length of the coilover? :confused:

Ok, I understand that regardless of how much preload is used, the spring rate will be the same. Both Linear and Progressive springs?
So with that aside...

Can't we use preload to tune how the car initially shifts its' weight?
Using my example from before, the springs won't compress till 250kg+ is put on each corner. So if we knew how much force was thrown onto the fronts when 50% brakes are applied @ 100km/hr. Then couldn't we tune it to minimise nose diving/lift/body roll? By doing this, we can balance the cars' weight out or add bais front/rear, therefore giving us maximum tyre grip?

I'm not sure what I'm getting at. I can't find the answers cause I've forgot what my question was.

Yer, I've lost the plot *cries*

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Originally Posted by nigs

I understand that it maybe best to run 0 preload, so that there is MAXIMUM suspension travel. But what about in the old days where the only way to lower a car on coilovers was to preload the spring?

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Lowering requires you to lower the spring perches, preloading involves raising the perches to the point where the spring starts compressing, as the shock cant extend further.

The thing that I think is important to understand, and hasn’t yet been discussed is this.
With these common coilovers that you raise and lower ride height by the spring perches, the ones that don’t offer separate independent height adjustment, the preload is basically almost always at zero, here’s why.

When you install these coilovers in your car, it is very likely you will be lowering your car an inch or more. I believe and have heard that when the coilovers adjustable spring perch is set between its recommended ride heights, that the spring is basically loose in the perches. The only time the spring is preloaded is when you raise the car above what the manufacturer recommends.

If you set these coilovers to have zero preload, just enough to hold the spring firmly, and then install them on the car, the car will usually be raised UP an inch or so above stock ride height. Almost always the perches are lowered from there, to lower the car to the desired ride height. Meaning that there is no preload on the spring.

Once again, the only benefit of using Coilovers that allow separate height and preload adjustment is the ability to alter the amount of bump and droop travel separately from the height.

So basically if you are using coilovers that adjust height using the spring perches, and your not reaching your bump or droop maximum travel limits, there is absolutely no benefit at all to running the same coilovers which instead offer both height and preload adjustment.

I don’t believe any of these types of coilovers would ever be reaching there droop limit on the street (maby on the rear wheels of a fwd track car, but as ive mentioned, its not a bad thing) there is not enough weight transfer to completely remove all weight from one corner and transfer it to the opposite corner on the same end, that would take more than 1.5g’s of cornering force.

The only concern is running out of bump travel (bottoming out), however, if the coilover is designed well, with correct spring rates, and the ride height is sensible, there should be no worry of this at all, even under really hard breaking.

From calculations, say the chosen spring rate will mean that the spring might compress a very maximum of 2” from extreme potholes etc. And droop a maximum of a inch, the coilover would then be designed with say 5” of total available shock travel, so that the car should never reach the maximum bump or droop travel (unless the user decides to drop the car on its guts). The coilover is then designed so that at the optimum ride height say a 2” drop, the shock sits right in the middle of its stroke.
What im trying to say, is that if you install any decently designed coilover, that adjusts height by the spring perches, and you keep your car at a decent ride height, you should never be reaching those bump and droop travel limits.

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Originally Posted by nigs

I understand that it maybe best to run 0 preload, so that there is MAXIMUM suspension travel.

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Its not so much that that you get maximum travel, the travel always stays the same. What is altered, is where the shock lies in its stroke, when the car is at its static ride height.

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Originally Posted by JasonGilholme

Do you know what makes all this really hard???

The fact that our cars aren't perfectly balanced. *bangs head on wall*

How do they go about adjusting corner weights? Do they adjust the preload or the height at the base of the coilover?

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If the coilover allows, adjust the height, at the base of the coilover.
In saying that, it’s perfectly fine to do it using the spring perches if that’s your only option. It won’t negatively effect your handling in the slightest, the only way it would, is if the shocks were now reaching there bump or droop travel limits after you adjusted the corner weights via the spring perches.

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Originally Posted by nigs

Preload will give more bump travel but less droop?
And vice versa?

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Correct

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Originally Posted by nigs

But wouldn't preloading, shorten the overall length of the coilover? :confused:

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No, the shock can only extend so far, to preload the spring involves you to tighten the spring perch upwards, compressing the spring. Since the shock cannot extend further, the overall length of the coilover will remain the same when adding preload from zero. This is done with the coilover out of the car.

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Originally Posted by nigs

Ok, I understand that regardless of how much preload is used, the spring rate will be the same. Both Linear and Progressive springs?

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No, progressive springs make things complicated. All of what I’ve been talking about so far is regarding linear springs. Adding preload to progressive springs will effect where the car sits along it progressive spring rate curve, at static ride height. Meaning, that adding preload to progressive springs will progressively make the ride stiffer.

Say an un-preloaded progressive spring starts at a rate of 5kg/mm which increases as the spring compresses, the spring may start at 8kg/m along the springs same progressive rate curve, if the spring is preloaded.

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Originally Posted by nigs

Can't we use preload to tune how the car initially shifts its' weight?

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Not really, see below.

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Originally Posted by nigs

Using my example from before, the springs won't compress till 250kg+ is put on each corner. So if we knew how much force was thrown onto the fronts when 50% brakes are applied @ 100km/hr. Then couldn't we tune it to minimise nose diving/lift/body roll? By doing this, we can balance the cars' weight out or add bais front/rear, therefore giving us maximum tyre grip?

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Good question, unfortunately the answer is no, not to any worthwhile extent.

The formula for calculating lateral (cornering) weight transfer is this:

Lateral load transfer (lbs)=
(Lateral acceleration (g’s) x weight (lbs) x CG height (inches)) / track width (inches)

When using the formula, say your calculating the weight transfer between the rear pair of wheels, you use the weight over both wheels.

Longitudinal load transfer (lbs)=
(Longitudinal acceleration (g’s) x weight (lbs) x CG height (inches)) / wheelbase length (inches)

For weight in this formula, you use the total weight of the car.

As you can see, the suspension wont change this, it is not a part of the equation. However in saying that, the suspension controls body roll etc, and this effects how far the CG moves therefore very slightly effecting weight distribution.

It is better to control body roll with stiffer springs or swaybars, than to do it by limiting how far the suspension can compress or extend.

As for diving and lift, controlling that is what anti dive and anti lift geometry is for, it effectively controls the stiffness of the suspension under brakes/acceleration without resorting to mechanically limiting suspension travel, that isn’t done as per normal, smoothly by the spring.

I greatly recomend these books to anyone keen improve their knowledge on suspension:
Tune to win, the art and science of race car development and tuning. By carrol Smith
Race car engineering and mechanics, by Paul Van Valkenburg

The top one is more in depth and is a supurb read, the next one covers lots more areas, so less of the technical suspension stuff, it has a good section on fwd racing though.

Nice.
I think I got my answers.

Great info Muzz. :D

Muzz you friggin nerd!!!

Come and tune my suspension! :D:D

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Originally Posted by JasonGilholme

Muzz you friggin nerd!!!

Come and tune my suspension! :D:D

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lmao:cool:
Your on the goldy too, im keen to hit up some motorkhana's with ya:thumbsup:

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Originally Posted by bennjamin

if you preload too much , you are compressing the spring without static or dynamic load on it. This increases the spring rate and is only relevant to single perch adjustable suspension ( Tein SS for example)
Dual perch adjustable , as said only needs the upper perch adjusted to hold the spring captive. The lower perch is to adjust the height. The static spring rate does not change

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It doesn't increase the rate, it increases the amount of energy stored in the spring to begin with. It's usually only used in competition vehicles with serious download or in offroad applications. In both cases it's adding extra load to move th espring but the spring still behaves with the same rate once it's moving.

This is a tricky area and still open to some debate between engineers about what works where. We've run aero cars with no pre load and no droop limiting with great success but then we have other teams running bucketloads of preload and are just as quick as us.

These things were sent to try us.............

I have to say this is one of the best threads I've read on here in a long while.

Thanks to everyone for making some great posts, Muzz in particular, you're the man!