General Suspension help.

[ekslut]

I've just started my mechanical engineering course too

Spring Pre-Load - Compressing a spring in advance of adding a load.
Example: Using a 100 pound linear-rate spring, preloaded one-quarter inch, would take twenty-five pounds of force before it would further compress. In effect the spring will not compress until 26 pounds of force were applied. The spring in this instance will only move one-quarter inch when 50 pounds of force were applied, as opposed to the half inch the spring would have normally moved.

I think what 'Muzz' was saying is correct (If I am reading it all correctly). If the spring is 100mm with a spring rate of 10kg/mm and is already pre-loaded 20mm then it will need over 200kg of force to get it to compress anymore. The actual spring rate has not changed, as it will stay to the same rate; @400kg of force it will compress 40mm, which is only another 20mm over what it is pre-loaded at.

Therefore the more its preload it means that the spring will need more force applied to it before it starts to work as if it didn't have any pre-load. Meaning this is why it 'feels' like it is stiffer.

This has turned into a very intresting thread

[Muzz]

yeh it has, i love talking and thinking physics.

[BlitZ]

wow... u boys should open and engineering shop..

sounds very reasonable -

i have now established the meaning of preloading...

but is it feasible now on a coilover?

you would need to preload the coilover harder than the weight of the car for it to work?


if you spring is to compress a few mm's as u sit your car back down.. then you preloading didnt work...

you proabably must exceed the cars weight by a fair bit before it takes effect and is this possible with a hand spanner?

With all this said... your shock would not bottom out.. it would top out and go THUG as you air bourne abit and your coilover would proabably pop a socket


and also with the single adjustable coilovers.. you would need to raise your car higher to actually preload it... is it even possible? as they simply run assister springs to keep it captive

[ekslut]

hmm.....I think what you are saying is true, kind of. The average spring rate seems to be around the 10kg/mm mark, and the average civic is about 1000kg. Some of the cars weight will be the force applied on the pre-load, which for the average civic means if you pre-load the spring about 25mm, it will be at its 'base' point.

But as the quote that I posted from the zeal site said, they already come pre-packaged at the correct pre-load, which I am assuming is to take into the account the cars weight (I could be wrong). This means they are allowing adjustment for more. Anymore than the standard pre-load and you are pre-loading the spring more, which will give the 'feel' of a stiffer spring, any less and it will give the feel of a softer spring.

[ekslut]

With all this said... your shock would not bottom out.. it would top out and go THUG as you air bourne abit and your coilover would proabably pop a socket


and also with the single adjustable coilovers.. you would need to raise your car higher to actually preload it... is it even possible? as they simply run assister springs to keep it captive

Yeah, I am not saying that pre-loading the spring heaps to get a stiff ride is a good idea. I personally would leave it at the factory level, maybe a little modification to adjust for the cars weight, or to adjust for a little bit of stiffness/softness. I wouldn't be straying too far from the factory setting though.

I would be using the bottom adjustment for the height.

[BlitZ]

Yeah, I am not saying that pre-loading the spring heaps to get a stiff ride is a good idea. I personally would leave it at the factory level, maybe a little modification to adjust for the cars weight, or to adjust for a little bit of stiffness/softness. I wouldn't be straying too far from the factory setting though.

I would be using the bottom adjustment for the height.

yeah.. i know exactly what u are saying..



i just dont think thats y they designed it... they preload to hold the spring in place and not to compress it.. and as mentioned its not easy to compress a spring more than 2-3 cms... and thats a 10kg/mm spring.. most are about 6-7...

and if u adjsut the height form the bottom.. it will always give u the optimum hsock travel regardless of how low your car is..

[ekslut]

i just dont think thats y they designed it... they preload to hold the spring in place and not to compress it.. and as mentioned its not easy to compress a spring more than 2-3 cms... and thats a 10kg/mm spring.. most are about 6-7...

and if u adjsut the height form the bottom.. it will always give u the optimum hsock travel regardless of how low your car is..

It isn't easy to try to compress the springs, but I dont think its designed to really compress them a lot. I think its there as a fine tuning tool, not for large adjustments which would be hard to do.

I think if it was there to just hold the spring in place it would not be adjustable. They would just make it fixed, which would save people stuffing up there coilover settings and it would be probably be cheaper to do too.

And I agree it is best to adjust from the bottom for height.

[ekslut]

This has got me intrested, so I have sent a e-mail to zeal asking what the preload of a EM1 is, and what they take into account when they decide the standard reload.

So we shall see what the answer is.

[BlitZ]

This has got me intrested, so I have sent a e-mail to zeal asking what the preload of a EM1 is, and what they take into account when they decide the standard reload.

So we shall see what the answer is.

when you say preload.. they might just think your talking about the spring rate and why it is what it is.

[Muzz]

i think iv worked out what it is. itll take me a while to explain, but i think in effect, the main purpose of seperate height and preload adjustment is actually change the height of centre of gravity during cornering! yes this sounds really really whacked out but let me explain. ill use diagrams aswell, just be patient.

[Muzz]

*READ SLOWLY AND CAREFULLY*

you would need to preload the coilover harder than the weight of the car for it to work?

thats a very interesting thought.

say each corner of the car weighd 300kg, and the spring were preloaded so they pushed up with a 300kg force aswell, placing the car on the ground would not compress the coilovers at all! so therefore if the car got air or watever, the coilover would not extend any further that if the car was at rest on the ground.

the same situation without preload springs the car would sag down compressing the coils with its weight.


in the 1st case, the car has no negative suspension travel (where the coilover can extend longer than its legnth when the car is at rest), and in the second case it does.
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With all this said... your shock would not bottom out.. it would top out and go THUG as you air bourne abit and your coilover would proabably pop a socket

exactly.
and increasing the preload ABOVE the weight of the car would be dangerous, as when the coilover is compressed and released, it would extend and hit the top of its stroke with even more momentum, which would lead to sudden decrease of weight on the wheels, as the coilover hit its top.

i think all cars must have negative susp. travel (watch them get jacked up off the ground), it sounds dangerous otherwise.
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adding preload from having none at all, will push the car upwards, and thinking about it now, adding preload wont change the force needed to compress the coilovers a given amount, compared to having no preload.

eg. the corner of a car pushes down with 300kg of force on a coilover which has say 200kg of preload pushing up.The cars weight will overcome the preload anyway, leaving the spring to work as normal.

Think about all this carfully before reading on.

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What changes by adding preload is the ride height, but also the amount of negative suspension travel the coilover can experiance.

eg. as before 300kg of weight on a coilover with 300kg of preload, will not compress from the weight of the car alone. therefore at rest the shock has no negative suspension travel.

and with no preload, the car has the ability to extend the shocks, because there already compressed, allowing negative suspension travel.
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Its clear to me now, that coilovers that allow seperate height and preload adjustment allow you to keep your optimum ride height, while adjusting the amount of negative suspensin travel.

ADJUSTING THE AMOUNT OF NEGATIVE SUSPENSION TRAVEL ON A CAR HAS A VERY INTERESTING EFFECT DURING CORNERING!

im at uni now so wait till i get home and can explain with pics, imposible for me to otherwise, but reducing the amount of negative suspension travel available actually causes the center of gravity to be pulled lower to the ground during cornering, i researched this for a yr 12 report in 2004

[Muzz]

Suspension travel
The amount of negative suspension travel (how far the suspension arm can extend) can have a huge effect on the cars handling; it influences both the amount of roll and the amount of pitch the chassis will experience during a corner.

In this picture we see a car with a lot of negative suspension travel as the chassis rolls into a turn. The chassis is free to roll, and the height of the CG (centre of gravity) doesn't change very much.



In this picture we see a car with almost no negative suspension travel as it rolls into a turn. The chassis is pulled down as it rolls, effectively lowering the CG.


So, if one end of the car has less negative suspension travel than the other, that end will be forced down more in a turn, which makes for more grip at that end, especially in the middle part of the turn, where weight transfer is at its strongest. Very little negative suspension travel at the front will give a lot of steering, especially when entering a corner at high speed, or very violently. Very little negative suspension travel at the rear will give a lot, and consistent traction throughout the turn.

The amount of suspension travel also influences the car's longitudinal balance, i.e. when braking and accelerating. An end with a lot of negative suspension travel will be able to rise a lot, so weight transfer will be more pronounced. For example: if the front end has a lot of negative suspension travel, it will rise a lot during hard acceleration, transferring a lot of weight onto the rear axle. So the car will have very little on-power steering, but a lot of rear traction. A lot of negative suspension travel at both ends, combined with soft springs, can lead to excessive weight transfer: on-power understeer and off-power oversteer.