Preloading, how to tune it?

[JasonGilholme]

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

[Muzz]

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.

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.

[Muzz]

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?

thats correct

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?

Exactly

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).

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.

[Muzz]

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

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.

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.
.................................................. .................

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.
.................................................. ............

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)

[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?

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.

[nigs]

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?

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*

[Muzz]

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?

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.

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

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.

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?

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.

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

Correct

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

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.

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

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.

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

Not really, see below.

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?

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.

[nigs]

Nice.
I think I got my answers.

Great info Muzz.

[JasonGilholme]

Muzz you friggin nerd!!!

Come and tune my suspension!

[Muzz]

Muzz you friggin nerd!!!

Come and tune my suspension!

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

[EfiOz]

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

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.............

[Chris_F]

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!