Coilover advice from the experts?

[Caveman]

Hi guys,

I have been running new coilovers for the last few months, but haven't been able to set them up how I want them. The reason for the purchase was to improve the handling characteristics of the car (reduce roll, improve steering response etc) but also for the cosmetic improvement of a lowered car.

I currently have 8kg springs on the front and 6kg rear which I understood from other people's experiences is about right. I have my front dampers set at 15 clicks out of 32, and rears at 7 clicks from softest.

The car certainly rolls a lot less, but I cannot get the suspension to perform optimally with the current spring rate. If I set the dampers softer, the car bounces too much and grounds out at speed on irregular surfaces. If I set the dampers harder, the car hops over rough ground and I end up out of my seat half the time - practically undriveable.

Guessing I might have trouble, I did invest in both softer and harder springs when I bought the coilovers for experimentation. The questions is, do I go harder or softer? I have a pair of 4kg springs, 10kg and 12kg.

My guess was to go softer, but I'm worried that the car will ground out or hit the bump stops even more. At the same time, won't harder springs make the car even more undriveable over rough ground?

My final thought is that perhaps my car is just too low, but I'm sure that it's not exaggeratedly low - here's a photo:

http://www.agog-digital.com/vr4/03.jpg

Be really interested in anyone's thoughts as to the best solution.

Cheers guys! :thumbsup:

Mart.

[White Lightning]

That does look pretty low to me.

What make are the coilovers?

[Caveman]

Thx for the reply. So you think it's too low then? There's still plenty of ground clearance, so I thought it seemed ok, but maybe it is.

The coilovers are ones I sourced myself from a Far East manufacturer, but they seem good quality. I'm sure it's either the springs rate or the car's too low.

Just dunno which! :D

Cheers,

Mart.

[peter thomson]

My car is slightly higher with with 10kg on the front and 6 on the back with the preload set as far as they go. No grounding but i would prefer the fronts to be a bit harder and may go that way depending on the outcome of my front springs being rusty after only 4 months on the car. Shock adjusment are both at max and this is one of the reasons I think I need stronger front springs.
Have you checked the camber with them that low as that could be upsetting the handling as well

[Caveman]

Peter, so how does your car behave over rough ground and sudden dips? Does it absorb bumps and dips without unsettling the car, or does it hop or crash?

Mart.

[Caveman]

Thanks for your replies so far, just an update. I just had a chat with the suspension guru at Powerstation who develops the AST suspension kits for Litchfield's STIs and he says that for road use, softer springs and harder dampers is the way to go.

He said on the STI for example, he runs 5kg front and 3kg rear, and he recommended I go softer than I am. He said that 10kg or 12kg would be way too hard for a road car.

I am thinking about trying 6kg front and 4kg rear and seeing how that goes, but I would appreciate people's guidance and experience.

Mart.

[peter thomson]

So far it has been fine with sudden dips but I do get the occasional hop when on fast bends where there are nasty potholes. I wouldn't say that i have any "crashing" with the setup at the moment . i would like stonger spring on the front so I can dial down the damper settings though

[MikeKey]

If I set the dampers softer, the car bounces too much and grounds out at speed on irregular surfaces. If I set the dampers harder, the car hops over rough ground and I end up out of my seat half the time - practically undriveable.

Harder springs would seem to be the next thing to try. You're already low, and if you're bottoming out with the springs you have on, the last thing you need on there are softer ones I'd have thought?

[Louis]

Hi,
This is a link to my set up, I posted settings etc,

http://www.clubvr4.com/forum/showthread.php?t=13851

try tightening up the pre load on the spring for less travel

[Kenneth]

The lower you want to go, the harder your springs will need to be.


One option you have is to wind the preload right up so that your initial height (static ride height) is higher, that way you are not going to hit the ground as often. Best would be to get stiffer springs though. Personally I was happy with 12kg front and 8kg rear.

It also sounds like your damper settings are too stiff for low speed driving (around town etc) and are probably making your car feel bouncy and uncomfortable.

With 12kg front and 8kg rear I was using damper settings of 6/32 front and 4/32 rear in the Legnum. This was a fairly comfortable ride and one that Jo was happy with also.


You have to be careful with the damper rates as dampers are not designed to stop you bottoming out. They are there to stop the springs from bouncing and as such they need to be matched to the spring rate and the expected travel. Around town the expected travel is high (pot holes etc) and you need to have the dampers soft to avoid damage to dampers, wheels etc. not to mention preventing headaches from a jarring ride

[Louis]

Don't know how much adjustment you have on your coilovers, but on mine, I can pre load, (or squash )the spring by adjusting a collar so the ride is harder, and then lower the ride height with a different collar. Like this, the car is low the suspension is stiff and the spring has less travel (same spring, less travel)If you don't have seperate spring pre load, then all you can adjust is the ride height, you can't pre load or squash the coil spring.
You got a photo?

[Caveman]

Hi Louis, yes I have separate preload adjustment and height on mine as well as damping. These are the fellas:

www.agog-digital.com/vr4/shox.jpg


On another note, Kenneth, would you say my car was too low? How low is yours in comparison?

Cheers,

Mart.

[Louis]

Mine is about 2cm clearance between tyre and arch, but I dont have probs with arch tyre contact, I do have some issues with speed bumps, but not too many.

Should be a pic of my car here

http://www.clubvr4.com/forum/vbpicgallery.php?do=big&p=1416

[Kenneth]

On another note, Kenneth, would you say my car was too low? How low is yours in comparison?

Cheers,

Mart.

Mine was a little higher than that but not a great deal. how far is your preload wound up? I find as a general rule that if you wind it as far as you can with a c-spanner and just your hands, then it is about right. Again, this will depend on your spring rate.

If you are bottoming out then it is too low for the spring rates. Either make it higher or put stiffer springs in.
It is the springs that keep you off the ground, the dampers are what control the ride quality. Stiff springs need harder dampers as the damper has to do more work for each mm of travel to keep the ride quality in check.

[Subaru ETA]

hmmmm, my legnum was lower then both of those in the links....(my rear wheels were in the arches pretty much!) and i never had it bottom out at speed (even when i had the speedo wound out on the road out to mangawhai) it had a real nice ride too. dont know what the setting were tho. had the tein coilovers in it when i got it.

my galant on the other hand just has lowering springs. not as low as the legnum, but has a nice ride. i have had it bottom out on the same road at 110km/h

so while ride hight is a factor in it bottoming out, it has to be other settings aswell

[Kenneth]

so while ride hight is a factor in it bottoming out, it has to be other settings aswell

Yep, the spring rate.

Bottoming out is all to do with spring rate and ride height. Or more specifically available suspension travel. If you reduce the available suspension travel (by lowering the car) then you need to increase the spring rate to compensate.

Example:
A spring rate of 10Kg/mm moves 1mm for every ten kilograms of weight placed on it.

So 500kg weight on that spring would compress it 50mm.

In cars this weight is the car, the compression is known as static sag. Static sag is the amount of height the car looses from the cars weight being placed on the springs. What is left between the car and the ground is your ride height.


So, if you have 150mm ride height available and you go over a bump that puts a shock load of 1000Kg on that wheel then 1000kg/10kg (spring rate) = 100mm of movement.
If you had 150mm of travel available then this wouldn't be a problem as you would retain a clearance of 50mm.

If you then lower your car by 50mm, you WILL have a problem as each time you hit this bump you bottom out.

If however, you change the spring rate to 12kg/mm then it works out a bit differently. 1000kg/12kg(spring rate) = 83.3mm of movement. You would now have 16.7mm of clearance when hitting that bump.

And that is really all there is to it as far as bottoming out goes.

[Caveman]

Hi Kenneth,

Thanks for the detailed reply and insight, very helpful!

I understand that a harder spring will prevent the car from bottoming out, makes complete sense. However, in terms of ride quality, surely 50% harder springs are only going to make the ride worse as they will be less likely to move and hence absorb bumps and irregularities in the road surface?

As I mentioned, I was advised by one of the biggest suspension tuning houses (Powerstation) that soft springs and hard dampers was the way to go for a road car.

You mentioned that you run 12kg front and 8kg rear - what is the ride quality like on bad surfaces? The roads where I live are pretty bad and at the moment I have to decide between a softer, but bouncy ride and risk bottoming out, or a crashy, jarring ride where the car is hard to control at speed.

Do you think that the ride quality will actually improve with harder springs - does your car absorb bumps and dips at speed on poor surfaces?

Be interested to hear how your car reacts with such hard springs.

Cheers! :)

Martin.

[djb160]

Just so you know I think that your ride height is spot on IMO, looks perfect.

[Kenneth]

It is the dampers that transfer shock to the vehicle body more than the springs. The springs absorb shock by moving.

So a stiffer spring is going to be more comfortable than a stiffer shock, as the shock absorbs energy into the spring whereas the shock stuffs most of it straight into the car body. This is the discomfort you feel.

The whole point is that you need to have the damper matched to the spring so that both do work. With soft springs and hard dampers, you might as well not have springs. As such, no wonder it feels like you are driving around without any!

12kg front 8kg rear were fine with the damper settings low. At low speed on extreamly uneven surfaces it is bumpy, but you cannot get away from that with conventional suspension if you wish to ride low but remain safe.

Powerstation? Where abouts are they, I have never heard of them. It also appears to me that the person you talked to (as this is usually what it comes down to) didn't know their ass from a hole in the ground or is grossly misinformed.

Soft springs and hard dampers must be bloody uncomfortable it makes me wince just thinking about it.

btw, I would hope you have strong top-hats on the suspension too, as that is where the damper is placing all the shock. If you hear stories about people destroying the top-hats on their suspension, I would lay money that damper rates that are too hard for the springs is the reason why in 99% of cases.


Hi Kenneth,

Thanks for the detailed reply and insight, very helpful!

I understand that a harder spring will prevent the car from bottoming out, makes complete sense. However, in terms of ride quality, surely 50% harder springs are only going to make the ride worse as they will be less likely to move and hence absorb bumps and irregularities in the road surface?

As I mentioned, I was advised by one of the biggest suspension tuning houses (Powerstation) that soft springs and hard dampers was the way to go for a road car.

You mentioned that you run 12kg front and 8kg rear - what is the ride quality like on bad surfaces? The roads where I live are pretty bad and at the moment I have to decide between a softer, but bouncy ride and risk bottoming out, or a crashy, jarring ride where the car is hard to control at speed.

Do you think that the ride quality will actually improve with harder springs - does your car absorb bumps and dips at speed on poor surfaces?

Be interested to hear how your car reacts with such hard springs.

Cheers! :)

Martin.

[MikeKey]

The basic idea is that the springs are for controlling compression, i.e., how far and how fast your wheel will travel up into the wheel arch, and dampers are for "damping" the rebound action of your springs after they've been compressed.

Dampers shouldn't be doing the work of absorbing bumps, the springs should be. Dampers are just there to control the movement of the springs after they've absorbed bumps. If you drove a car with the right springs and no damping at all, it wouldn't bottom out. What it would do is feel like a fairground ride, because your uncontrolled spring rebound would be bouncing the car all over the place! That's where the dampers come in.

For this reason, setting your suspension up with soft springs and hard dampers is daft.

Besides the fact your dampers will be transmitting almost everything that isn't absorbed by your tyres straight to your suspension turrets, as has already been mentioned, the time it takes your suspension to recover from a hit with a setup like this will be far longer than it should be.

After a few nasty hits in a row you'd still be bottoming out, simply because your dampers would be so compressed as a result of there not being enough spring force to re-extend them in time between hits.

Fun and games eh?! :pimp2:

[White Lightning]

Messed about with my Tein setup a bit at Castle Combe at the weekend ... I had the dampers set to 10/32 front and rear for the first track session (that is the number of clicks from the hardest setting). This is the setting that I use on the road and I wanted to see what it was like on track. Too soft was the answer. So, for the second session I tried 6/32 front and rear. This made the car feel so much more stable and I would say barreling into Quarry corner where there is a big dip at high speed is a good test for the suspension and mine felt planted with this setup.

As for the spring rate, I would have to check as I can't recall what the Super Wagons are ... the ride height you can see below ... (really just a blatant excuse to show this picture again as I love it :pimp2: )

[Caveman]

Hi guys,

Thanks for all the useful replies so far!

So from what you're saying, if I want my car to have a smooth ride I can't have it as low as I have it now, as a smooth ride requires soft springs and a higher ride height.

If I want to maintain my ride height I need harder springs to stop the car bottoming out, which will in turn allow me to set my dampers a little softer.

Right?

So is the general consensus that 12kg front and 8kg rear is right for a very lowered car?

Thanks again,

Mart.

[MikeKey]

You can still have a smooth(ish) ride with harder springs if they're progressively wound...

[Kenneth]

Even at 12/8 (front/rear ) you may have to raise the car a little. As I said, my car wasn't as low as yours is.


Hi guys,

Thanks for all the useful replies so far!

So from what you're saying, if I want my car to have a smooth ride I can't have it as low as I have it now, as a smooth ride requires soft springs and a higher ride height.

If I want to maintain my ride height I need harder springs to stop the car bottoming out, which will in turn allow me to set my dampers a little softer.

Right?

So is the general consensus that 12kg front and 8kg rear is right for a very lowered car?

Thanks again,

Mart.

[Nutter_John]

i have 14 front 10 rear and run at 70 mm lowered , i have upped the preload by 10 mm and do not bottom out at all ,tis a firmish ride but not that bad , dampers are set around halfway . On a track it is just spot on for grip and ride , altough i may tighten them up a little more for the next one

[Caveman]

To get the front vs rear spring rates right, does anyone know what the weight distribution of the legnum is? I am assuming that the front is significantly heavier than the rear?

I currently have 6kg on the rear and that seems fine, although harder to tell when you're sitting in the front!

Cheers,

M.