General Suspension help. [Archive]

Muzz

05-04-2006, 10:34 AM

Hey guys im heading down to the bank next week to apply for a loan for some car parts, and im after some advice.

Heres my situation.
iv got a 99' ek4 hatch, that iv brought to build into a weekend track car. Im at uni for the next 3.5yrs and cus of a lack of money im concerntrating soley on the handling of the car(also reducing the weight). Later on during my course i wish to go all out on the brakes, but im not thinking of that yet cus its a long time b4 i start tracking. Basically when i finish my degree, I wanna have my civic completly ready for racing, so all i have to concerntrate on is building a crazy wild n/a engine too complete the car. At this point id probably buy a cheap economical runaround and garage the civic for track work.

So far My list of parts im thinking of are:

1. Tein SS coilovers - only cus ill be driving street for 3.5 years yet, and still want a little comfort, upgrade later for track.

2. Swaybars - i already got these, whiteline F 24mm, R 22mm, and an asr subframe brace

3. Camber and caster kits

4. front and rear strut braces.

What else should i include in my list of goodies for awsome handling? im not to interested in extra bracing yet cus id like to have a propper structual roll cage built later on, so till then its just the strut braces.

i feel theres more things im missing on my list, i wanna go all out on the suspension and leave no stone unturned, and pay for everything i need in the one go with the loan.

ekslut

05-04-2006, 11:00 AM

I think you got most of it covered. Look at getting some polyurethane bushings to replace the soft standard ones. You can get some lower arm tie bars front & rear, rear control arms (wont really help handling all that much, but the bushings should be better in them, and they should be lighter weight).

Thanks about all I can think of now....

Also why dont you get some better coilovers and run them on their softer setting for the street? Saves you buying them twice, and you can just adjust the damper to get them harder for when you want it.

Muzz

05-04-2006, 10:53 PM

cheers mate very helpful, yeh gunna add poly bushes to my list, and considering what ur saying about getting a good set of coilovers straight up.
with coilovers, do they have a lifespan, or with regular servicing do they just keep on going without any change in there performance? anyone here been using the same set for say 5+ years?
some coilovers iv seen say seperate height and spring preload adjustment, does this mean that they can be adjusted in a way that changes the spring stiffness? (adding extra preload makes the spring act stiffer maby???)

ekslut

06-04-2006, 08:33 AM

yeah, coilovers like most products do have a lifespan. But if you get a set thats servicable in Australia, then it should be fine. I think Tein are servicable, so its just a matter of getting them serviced when they need it.

You can get coilovers that have 2 way height adjustment. Most height adjustable coilovers have the adjustment using a perch the spring sits on. You can adjust this up/down, but it will change the spring stiffness. From memory, the more you comress the spring, the stiffer the spring will be. 2 way height adjustable coilovers also have the bottom part of the coilover able to screw up/down to adjust the height. This doesn't effect the spring loading.

BlitZ

06-04-2006, 09:42 AM

You can get coilovers that have 2 way height adjustment. Most height adjustable coilovers have the adjustment using a perch the spring sits on. You can adjust this up/down, but it will change the spring stiffness. From memory, the more you comress the spring, the stiffer the spring will be. 2 way height adjustable coilovers also have the bottom part of the coilover able to screw up/down to adjust the height. This doesn't effect the spring loading.

I do not believe this to true.

most coilovers have a linear spring rate and shouldnt get "much" harder as u go lower...

the 2 way adjustment is to give more/optismise shock travel... (in the cente) and not for spring hardness

The more u are able to extend the shock rod the better.. that why race shocks have such a short bodies as this allows the shock piston to have sufficient travel. Its a great advancement how they have incorporated this theory into the current coilovers

ekslut

06-04-2006, 09:56 AM

Really? Guess I was wrong then. I always though it made the springs feel more/less stiff as welll. Not in huge amounts, but noticable amounts.

You learn something new everyday :thumbsup:

ekslut

06-04-2006, 10:17 AM

Did some quick research on this, and taken from:
http://www.endlessusa.com/faq/#t12 (http://www.endlessusa.com/faq/#t12)

Q: Can I raise or lower my car by adjusting the spring seat/perch?
Adjusting the spring tension by way of the spring seat/perch and seat/perch lock may slightly affect the height of the vehicle. Tightening it greatly will raise and loosening it greatly will lower the vehicle slightly, but we DO NOT recommend using this mechanism for height adjusting reasons. This is specifically why our Function Series coilovers include the independent, lower, height-adjustable bracket/cup.

Q: Then what is the spring seat/perch and seat/perch lock used for on the coilover? And what are your recommendations on adjustment?
For performance reasons. Adjusting this mechanism creates different "spring preload" or spring tension. Although our systems come assembled and prepackaged at the recommended settings, to reset the spring preload, simply loosen the spring seat/perch and seat/perch lock until you have play with the spring. Do this when the coilover is off the vehicle. Hand tighten the spring seat/perch and seat/perch lock until there is no play. This is considered the zero point. Our recommended ranges are between the zero point and two full turns.

So to find out what the spring preload means when it is adjusted I found this:
http://www.worksperformance.com/html/tpl_desc.html

Threaded Spring Preload is used to change the amount of sag or ride height. You adjust the threaded collar, which compresses the spring, and that will increase spring pre-load. Increasing Spring Preload moves the spring further into its travel and makes the shock “feel” stiffer initially, and makes the chassis sit a little higher.

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.

So from what I can gather from this info is that when you increase the adjustment for the spring preload, it does actually make the spring 'feel' stiffer, as there will be less movement by the spring.

Muzz

06-04-2006, 12:03 PM

thanks that helps heaps, can u guys think of any other brands of coilovers that have service support in australia?
What about buddyclub? i see they got dealers in aus but there all in vic and nsw, im up in SE queensland.
Has anyone had any experiance with whitelines group 4 coilovers, there expensive at $2800 but i dont mind paying for quality.

Heres what they say:
"But if you're looking for real road performance get excited about our all new Group 4 shocks. These are height and rate adjustable with no need for yearly maintenance (unlike others) that's right, maintenance free.

Specifically designed for performance road use, the high pressure mono-tube design utilises a class leading 46mm piston. Our unique top mounted composite bump and rebound rate adjuster changes only what you need while height adjustment doesn't require multiple C spanners. No need to lie under the car with a torch to adjust the rate, just lift the bonnet and adjust as required. Non-inverted mono tube design also means no stiction and noise problems like other road/rally hybrids.

Careful attention to spring and damper base rates makes them ideal for serious road and race use right up to slicks and weekend race sprints. Designed as part of the Whiteline system to mix and match with our range of swaybars, alignment aids and chassis bracing.

You can have it all... if you're serious.

Whiteline Group 4's are leading the field in tarmac rally and club motorsport:

1st outright team and driver 2004 Dutton Rally NSW - Whiteline Project EVO VIII
3rd outright team and driver 2004 Dutton Rally Vic - Whiteline Project EVO VIII
2nd outright team and driver 2004 East Coast Targa - Whiteline Project EVO VIII
1st outright team and driver 2005 Dutton Rally Qld - Whiteline Project EVO VIII
2nd outright team 2005 Dutton Rally Qld - Impreza STi 04 driven by Shane Topping"

Being supposedly maintenance free, im shur theyd help with the extra cost aswell.
i like the fact that the shock bump and rebound can also be seperatly adjusted (i used to race R/C cars and the part i loved most was tweeking the cars sussy setup, which was completly adjustable. toe, camber, shock stiffness, interchangable springs & swaybars etc.)

However im even more keen to find a set that has seperate height and preload adjustment. i believe tein flex has this feature, how do they rate for trackwork? anyone have idea of spring rates?, cant seem to find them on the net for a civic ek4 hatch, herd these maby illegal in australia?

Im also looking at maby buddyclub racing spec damper, which are supposedly street - circuit, between the n+ and the track only coilovers. however they dont seem to have seperate height and preload adjustment, and im unshur of weather these can be serviced up here.

Anyone kno of any other good quality coilovers - more orientated towards track work, that has seperate height and preload adjstability, and can be serviced in aust.

Muzz

06-04-2006, 12:14 PM

bennjamin

06-04-2006, 12:56 PM

would i be correct in thinking that companies eg. fulcrum suspension, wont service other brands of coilovers?

fulcrum suspension dont seem to stock tein flex, does anyone kno if they can still service them?

It all depends on the coilover type etc. Some can be rebuilt while others cannot. Its up to you to email or call them and find out !

BlitZ

06-04-2006, 01:07 PM

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.

its interesting .. the question is : -

if the spring was 30cm high would the force at 30cm be the same if it was already compressed to 25cm...(where are the engineering students)

considering it was linear i thought it would be the same (as suggested its hooke's law)-

EXTRACT from HONDA-TECH :thumbsup:

"sounds like both of you are confused about Hooke's law and how a linear spring works. "preload" doesnt affect anything about a springs function. a linear spring exerts the same amount of force from being compressed 0-1" as it does from being previously compressed at 2" to being compressed another 1", basically 2-3". what is effectively changed is the ride height when you adjust the amount the spring is precompressed and the static cornerweights of each wheel. the fancy shocks that allow you to separately preload the spring allows the adjustment of ride hieght independently to cornerweights. "

Also refer to the link u gave... They are talkain about a progressive spring in a coilover... not a linear spring

So basically u cant preload linear

Muzz

06-04-2006, 02:27 PM

(where are the engineering students)

haha strange u should ask but im studing mechanical engineering.
Heres my opionion...

lets say we got a spring of 30cm with a 10kg/mm linear spring rate.
for now consider it OUT OF THE CAR.

lets say the spring is preloaded to 28cm, this is the same as compressing the spring with 200kg of force (2cm x 10kg/mm)

this in effect will mean the spring is pushing up with 200kg of force
(but it wont extend cus the shock/watever stops it from extending).

because the spring is pushing up with 200kg force, it wont compress at all until that force is equaled and exceded. 210kg of force will compress the unit 1mm, without the preloading, the unit will be compressed 21mm by a 210kg force.

After 200kg of force is reached on the spring, it will compress at the exact same rate, as usual.

consider 400kg force:
preloaded spring - unit compresses 20mm
unloaded spring - unit compresses 40mm

this is exactly what ek slut was saying

EXTRACT from HONDA-TECH :thumbsup:

"sounds like both of you are confused about Hooke's law and how a linear spring works. "preload" doesnt affect anything about a springs function. a linear spring exerts the same amount of force from being compressed 0-1" as it does from being previously compressed at 2" to being compressed another 1", basically 2-3". what is effectively changed is the ride height when you adjust the amount the spring is precompressed and the static cornerweights of each wheel. the fancy shocks that allow you to separately preload the spring allows the adjustment of ride hieght independently to cornerweights. "

sounds to me like this guys confused
preload does effect a springs function, it causes the spring to push up with a force, which has to be equaled before its compressed any further.
I believe what ek slut was saying is correct.

to compress a coilover unit 2in, the spring will be compressed 2in.
to compress a coilover unit 2in with 1in of preloading, the spring will be compressed 3in, which obviously needs more force.

preloading a progressive spring, is exactly the same as preloading a linear spring, in that no compressin will be achived until the compressive force is exceding that which the spring is pushing out with. both springs work exactly as usual when the preload is met and exceded.

so yes u can preload a linear spring.
The efect is the same as preloading a progressive spring.

ekslut

06-04-2006, 02:53 PM

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 :thumbsup:

Muzz

06-04-2006, 03:31 PM

yeh it has, i love talking and thinking physics.

BlitZ

06-04-2006, 03:46 PM

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

06-04-2006, 04:13 PM

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

06-04-2006, 04:16 PM

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

06-04-2006, 04:36 PM

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..:thumbsup: :thumbsup:

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

06-04-2006, 04:47 PM

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

06-04-2006, 04:57 PM

BlitZ

06-04-2006, 05:31 PM

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

06-04-2006, 05:55 PM

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. :p

Muzz

06-04-2006, 06:31 PM

*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.
.................................................. .................................................. ..

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

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.

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

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

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

06-04-2006, 09:43 PM

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.
http://i79.photobucket.com/albums/j126/Muzz87/wywy.jpg

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.
http://i79.photobucket.com/albums/j126/Muzz87/jfdgj.jpg

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.

Muzz

07-04-2006, 12:26 AM

mind you this is just my thoughts as to why some coilovers allow seperate preload and height adjustment, i could easily be wrong.

ekslut

07-04-2006, 09:03 AM

Very intresting. Sounds like you could pretty much be on the ball there Muzz. I got a reply from Zeal, and their preload is set a zero. So it actually doesn't come pre-loaded.

BlitZ

07-04-2006, 11:01 AM

to sum up whats explained - not sure if im correct here but this is what i make of it:

from Muzz's explanation:
no preload (spring can extend when weight is reduced) - when corning this would push the light corner up causing more body rolls??

BUT - take into consideration... alot of old type coilovers use really hard "short" springs and an assist spring.. the assist spring shouldnt be strong enough to push the vehicle higher in a roll and is simply used to keep the spring in place.

and also.. if your springs were preloaded so much ...it wouldnt have intial roll causing signifcant negtive travel in the oposing corner..

jsut my thoughts

Muzz

10-04-2006, 04:46 PM

BUT - take into consideration... alot of old type coilovers use really hard "short" springs and an assist spring.. the assist spring shouldnt be strong enough to push the vehicle higher in a roll and is simply used to keep the spring in place.

When cornering, the weight on the inside wheels is reduced yes.
basically if u have a coilover, assist spring or not, that compresses slightly from the weight of the car on it at rest, it will also extend (negative travel)when the weight of the car on that wheel is reduced ie, cornering.
The only time it wont extend during cornering, is if it dosn"t compress at all from the cars weight at rest.
a reduction in weight = extention of spring from origional compressed state.

and also.. if your springs were preloaded so much ...it wouldnt have intial roll causing signifcant negtive travel in the oposing corner..

say the car has 280kg of preload pushing up, the weight of that corner is say 290kg (preloaded HEAPS), that means when the car is placed on the ground the coilover units will compress as though 10kg of force is being applied to them (280kg preload upwards + 290kg downwards = 10kg force downwards).

Early on during cornering say the weight on the outside coilover increases from 290kg-295kg, that extra 5kg weight will go straight into compressing the coilover (280kg preload upwards + 295kg downwards = 15kg force downwards).

the weight of the car at rest has already overcome the preload, so compresses as normal during cornering. so any extra force goes straight into compressing the unit.

just my thoughts

BlitZ

10-04-2006, 04:57 PM

say the car has 280kg of preload pushing up, the weight of that corner is say 290kg (preloaded HEAPS), that means when the car is placed on the ground the coilover units will compress as though 10kg of force is being applied to them (280kg preload upwards + 290kg downwards = 10kg force downwards).

Early on during cornering say the weight on the outside coilover increases from 290kg-295kg, that extra 5kg weight will go straight into compressing the coilover (280kg preload upwards + 295kg downwards = 15kg force downwards).

the weight of the car at rest has already overcome the preload, so compresses as normal during cornering. so any extra force goes straight into compressing the unit.

just my thoughts

yeah but your spring would only compress like 1-3 mm if u had 10kg/mm springs.. which is like virtually no body roll.. and only 1-3 mm of negative travel in oppsing corner.

All im getting a :-

you cant preload the coilover equivalent or close to the mass of the vehicle...

If preloading the spring is used so negative travel is capped.. its pointless your wheel would simply get lifted from road contact.

and how would preloading solve the above issues (dual coils)

Muzz

10-04-2006, 07:18 PM

Ok it was an example to explain the effects of MAXIMUM preload. Im shur no one uses this amount.

if your springs were preloaded so much ...it wouldnt have intial roll causing signifcant negtive travel in the oposing corner..

i assume that ur saying body roll will be delayed by upping the preload.
i was trying to explain that even with almost max preload, the bodyroll would
begin the second that weight transfer starts begining, as with no preload.

yeah but your spring would only compress like 1-3 mm if u had 10kg/mm springs.. which is like virtually no body roll..

and only 1-3 mm of negative travel in oppsing corner.

yes the weight of the car would only compress the units 1mm (10kg/mm spring), while the car is at rest.
dont go thinking this is the max amount of bodyroll, its totally unrelated.

yes there would only be 1mm of avalable negative travel.

but there would stilll be body roll as normal.
say during cornering 50kg is transfered onto the outside wheels.
with a 10kg/mm rate thats 5cm the outside units will compress, while on the inside they can only extend 1mm.

All im getting a :-

you cant preload the coilover equivalent or close to the mass of the vehicle...
yeh agreed

If preloading the spring is used so negative travel is capped.. its pointless your wheel would simply get lifted from road contact.
not quite right, but i can see why u might think this.

car = 1000kg (250kg per corner)
during a corner, 100kg of weight transfers from inside wheels to outside (50kg each).

no preload - inside coilovers extend 5cm outside ones compress 5cm, inside weight = 200kg outside weight = 300kg

max preload - inside coilovers extend 1mm outside ones compress 5cm, inside weight = 200kg outside weight = 300kg

the weight on the wheels wont change between the situations.
The only reason in the 1st example that the outside raises up alot higher, is cause the coilover is pushing the ground and the car apart. even without this force the weight down on the wheel will still be the same.

and how would preloading solve the above issues (dual coils)
sorry i dont quite understand what issues?