Suspension Brakes 1st Gen Most liked posts in thread: Front Sway Bars?

If you have the front inside lifting the you most likely have a front coilover setup issue. Might "guess" that you might have preloaded your coilovers? How about sway bar preload?
I say 100% no to a front bar for you and am one of those that won't recommend a heavy front bar.

 

I have the TSW KW V2's and there is a fairly large amount of preload on the front. I did that to try and remove some of the rake that is in the stock car setup. I would previously never consider putting a larger front bar on the car. I whole heartedly think that if you are not scared of how loose your car is, it is not loose enough (well at least with a front wheel drive car). I do have my car corner balanced with driver weight, so I know there is no preload on the sway bars.

I will have to revisit my setup. I have the OS Giken diff and it hooks up pretty well (much better than the stock LSD) it just feels that there should be more there. Especially looking at some of the photos, I have never seen the wheel all the way off the ground, but it is definitely heavily unweighted.

 

Take out all coilover preload. You just cant preload this suspension.

 

I will see what I can do. The drop on the KW's for the R56 is pretty severe without preloading the springs some. How much rake would you recommend? If I add some rake back in, it will allow me to remove some of the preload on the front springs. If memory serves me, I have around 1/2 inch of rake measure at the jack points.

 

Reference point:

7/8" passenger side --- 1" driver side empty

320# springs front & rear

 

Thanks Alan, where are those measured from? the jack points?

 

Ok -- Please somebody explain "pre-loading" the coilover --- Thanks

 

On a lot of coilovers the way that you adjust ride height is by raising the lower spring perch. When you do this you are putting load on the springs. When you load up the spring when there is no weight on it, that is referred to as pre-load.

On some coilovers like the cross coilovers, you can adjust the entire shock tube up and down via a threaded portion on the bottom. Those types of coilovers allow you to change ride height independent of the spring loading.

 

This "Pre-Loading" of coilovers is a misused fad among these types of adjustable shock body coilovers that have become available, like the cross.
Pre-loading the springs should NEVER be done unless the suspension has been designed for such a thing. These would be on some sports racers, formula cars, ALMS, and such. BUT NOT on a Mini Cooper.

 

So if I raise the ride height on my KW V2 coils I am pre-loading?

 

I"m confused

seems to me pretty much all of the weaker springs will be pre-loaded to some extent. The idea that any pre-load is bad just doesn't make sense to me. What you want is when the car is at rest, there should be sufficient travel in both compression and rebound so that the suspension can do what it needs to do.

Let's look at an example. If you have a 200 lb/in spring on a corner that weighs 600 lbs, it's got to compress 3" to hold the car up. If the car only has 3.5" of suspension travel, and unloaded spring will be at rest about 1/2" from the bottom of travel. not a good situation. There is so little comression range left, that almost every bump will bottom the damper, and really kick the car hard.

While I think Greg may be on to something with this particular set up, (really, I don't know, it depends on the details) what one really wants to do is chose a spring strength and lenght such that a loaded corner has sufficient travel in both directions. This takes a bit more math than many do when selecting a spring.

Now, as the springs get stiffer and stiffer, this becomes less of an issue. They compress so little at rest that you end up needing "helper" springs that keep them on the perch cause at full extension, the spring won't even bridge the perches. If you don't have a helper, the spring will come off the perches, sit funny, and eventually re-seat with a bang and a discontinuous change in ride height! The is the definition of "upsetting the balance" for sure!

So really, check the car in question for how much travel there is both in compression and rebound, and see if the settings are way to close to one end or the other. If they are, the length/strenth of spring isn't well matched for the ride height that is the optimal for the suspension travel.

I'm not really aware of any single example on the boards where anyone has gone through all the math to make sure that all is good. Ryan posted some range of motion numbers for the R53 and R56 over on NAM a while ago, I think. I'm sure Greg went through all this will his car builds.

Matt

 

when someone is talking "coilovers" in the Suspension Modification thread, I do assume that they are running higher spring rates that are usually linear in rate. So this is why I state what I do. Of course soft springs with a progressive rate, like factory, are somewhat preloaded. But to pre-load an aftermarket coilover with a linear rate of around 350 lbs and up is not something you want to be doing.

It's why this topic came up. btwDriver said he was having a handling issue that I saw as most likely a Pre-load issue and in fact he stated that he preloads his springs.
Rebound is more important then compression in these cars and preloading spring just screws up rebound badly.

 

Onasled, when you figured out the spring rates for Bimmer Lite's MINI, were you able to install the coilovers with no preload? I ask this because you used spring rates that are significantly higher than what I have. I have 60N/mm rates which translates to around 342lb/in. You used 450 lb/in in the front and 500lb/in in the rear, if memory serves me correctly.

Between those numbers and the reduced rake I have in my car, that helps me explain why I had to increase the front preload.

Thanks for the explanation. I now feel I have a much better understanding of the issues.

 

With my Ledas

I have to run helpers with 325 lb/in springs, but I don't with 240 lb/in or so (I don't remember the exact rate that the softer springs I have are).

But with 325 lb/in springs, it's not a great street set up.

Matt

 

.....didn't mean to come off "harsh" with my last post. What I was trying to say is that I have a flaw in my responses as my mind set is usually on racing, tracking, and high performance road. So, they are not always the best post for the majority.

'btwdriver', I just never set a car up with preload but for the type I posted above (SRs, formula cars, etc). Important to start with setting up the front struts first and then tune the car's rake with the rear. After set-up is complete if I jack up the car, all four wheels off the ground, all springs are just sloppy loose, maybe from just slightly touching to 1" away from contacting the top spring perch. No helpers needed in the front, but the rears really need them. It's highly unlikely that one could loose spring to perch contact when driving the car unless you are on some major whoopdy-doos or if you re-bound is shot.
When you preload a spring you are shortening "full droop" which is a big no-no in a FWD car. I am talking about fronts mostly here. If you have cranked in pre-load then you are now riding very close, if not up against your internal rebound bump stops. So in your case when you unload the inside wheel in a turn you are severely un-weighting that tire, and in your case actually lifting it in the air. This is because you reduced your full droop severely.
I would worry way less about rake and focus much more on using your coilovers so they are in their "sweet spot". Start with the fronts and then work on the rears.
Oh, I should mention that you may have a spring length issue?? Six inch is good for all four corners with a good 0-20 lb rate helpers in the rears.

Greg V

 

Full droop is determined by the shock body on the unloaded side. At some point the laws of physics will tip the car and the shock body will raise the wheel when reaching droop limit. There are compromises on most any road course, its about establishing priority settings.

Stiffer springs up front will help lessen the ballistic impact from chassis weight, reducing dive on the loaded corner. Shocks designed for stiffer springs will generally have less droop, a softer spring will need to be longer, and shocks designed for softer springs will have more droop. btwdriver must pre-load his springs up front, if he didn't he would be ridding the bump stops the majority of the time. He's using KW dampers and springs, it's just the nature of his equipment.

 

This brings up a sad fact of aftermarket parts.

Most buy the coil overs, set the ride hieght by looks, and then think they have a race car. really, the way to go is close to exactly the opposite of what is commenly done. Like both Keith and Greg point out, the damper can only do it's job well if it's set up in it's sweet spot, with all the inhearent compramises of the design. This will, to some extent, set the ride height (unless that is independantly adjustable) and the dreaded wheel gaps. But then it comes down to this, do you want to look a certain way or handle a certain way...

I'm a big fan of form follows function, but I also understand that it's not the case for many. Anyway, live and learn.....

Matt

 

Yes

 

I have a good bit of experience with open wheel race cars. You are correct they very rarely if ever have any preload in the spring. The reason is not that you are limiting droop. Droop is controlled by the shock or strut. Race cars run spring rates that are high enough that it isn’t necessary to preload the spring. The real issue with soft springs is coil bind. The spring needs enough travel so you hit the bump stop before collapsing the spring coils into each other.
There is an affect from running preloaded springs. I am not sure if it is positive or negative, but with a preloaded spring you would likely have more weight on the inside wheel in full or close to full roll. The affect would depend on a number of things including the front sway bar. These types of things start getting very setup specific to track and driver.