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      09-10-2014, 10:43 AM   #1
cat-like
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Coilover Rebound Settings

Hi all. I want to share some experience I have had with my coilovers and see if anyone has had similar or some thoughts on it?

I had KW street comforts installed on my 1er about a year ago now. I also had had the rear subframe bushes changed to urethane and installed Whiteline front & rear sway bars (27mm & 20mm). Changing the rear bar probably goes against the thoughts of some on here but I made the decision to do it based on it was easier to do while the bushes were being done

Anyway, the street comforts were installed with a 25-30mm drop and the shop that installed them set the rebound in the middle front & rear (8 clicks from hard). I found the car handled beautifully and very neutral, this was confirmed at a track day where I was really happy with it. The only slight problem was as a DD, if I was picky the ride was a little too sharp. Maybe the bushings and sway bars contributed to this?

So eventually I softened the rebound by a few clicks to where the ride was very compliant. That created another issue - the back end became looser and slid around more. I experimented with different settings including making the front harder than the rear (which made it even worse) and there is no doubt that the softer the setting on the rear, the more the back end lost traction when taking corners with a reasonable speed. I adjusted the rebound harder (only down to 8 clicks from hard) and the more I made the setting harder, the better it stuck to the road. I found that making the front a couple of clicks softer than the rear created a good balance.

This is confusing, because everything I read says that it should be the opposite, especially with a stiffer rear sway bar.

Today, I read the paperwork again that came with my coilovers and I found recommended starting rebound settings that I hadn't noticed before:

Front: 9 clicks from fully hard
Rear: 6 clicks from fully hard

So apparently even KW recommend a harder rebound setting on the rear!

Am I missing something here?
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      09-14-2014, 06:51 AM   #2
recce
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rear sway bar too stiff.
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      09-14-2014, 12:58 PM   #3
Kgolf31
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Quote:
Originally Posted by cat-like View Post
Hi all. I want to share some experience I have had with my coilovers and see if anyone has had similar or some thoughts on it?

I had KW street comforts installed on my 1er about a year ago now. I also had had the rear subframe bushes changed to urethane and installed Whiteline front & rear sway bars (27mm & 20mm). Changing the rear bar probably goes against the thoughts of some on here but I made the decision to do it based on it was easier to do while the bushes were being done

Anyway, the street comforts were installed with a 25-30mm drop and the shop that installed them set the rebound in the middle front & rear (8 clicks from hard). I found the car handled beautifully and very neutral, this was confirmed at a track day where I was really happy with it. The only slight problem was as a DD, if I was picky the ride was a little too sharp. Maybe the bushings and sway bars contributed to this?

So eventually I softened the rebound by a few clicks to where the ride was very compliant. That created another issue - the back end became looser and slid around more. I experimented with different settings including making the front harder than the rear (which made it even worse) and there is no doubt that the softer the setting on the rear, the more the back end lost traction when taking corners with a reasonable speed. I adjusted the rebound harder (only down to 8 clicks from hard) and the more I made the setting harder, the better it stuck to the road. I found that making the front a couple of clicks softer than the rear created a good balance.

This is confusing, because everything I read says that it should be the opposite, especially with a stiffer rear sway bar.

Today, I read the paperwork again that came with my coilovers and I found recommended starting rebound settings that I hadn't noticed before:

Front: 9 clicks from fully hard
Rear: 6 clicks from fully hard

So apparently even KW recommend a harder rebound setting on the rear!

Am I missing something here?
Changing the rear bar IMO is necessary for our cars. I've experienced basically every possible damper change and alignment settings without adding a bigger bar and nothing helped solve the issues I was having with push and understeer. So you're on the right path with the bar.

You have to understand what rebound does to learn how to adjust it. You explain a rough ride with the dampers at mid-settings, but yet try to point the issue to the bushings and sway bars.

Sway bars only effect ride quality when one wheel is loaded (aka when you hit a pot hole).

Bushings will do some, but not to an extent.

Rebound controls how fast the damper returns to its stock length when the shock is compressed. A soft setting will allow the shock to return quicker than stiff. So, on a mid-setting...the shock comes to "rest" much quicker and with fewer oscillations than a soft setting. So the ride quality will decrease here.

Make sense?

So, now to the issue with the rear being loose.

First off, the dampers can only adjust so much. We have to look at your wheel/tire choices, alignment settings, ride height (are you running rake?), spring rates...etc. Unfortunately this isn't a simple solution.

As well, you have to look at the surface you're running on. A track will be much more grippier than the street, so you may have issues on the street versus the track. A setting on the street will never translate over to the track.

So, when we think about rebound, the best way to explain it is that the shock you're adjusting will effect the opposite side of the car. Front shocks will adjust rear balance, and rear will adjust front balance.

When you decrease rear rebound, you're affecting front grip. By turning the shock down, or soft...you're limiting the weight transfer from the rear to the front of the car. When you turn the shock up, or stiff...you're theoretically increasing weight transfer from the rear to the front.

Same would go for the rear.

So, when I set up my rebound typically I'm around 1.75 turns/2.25 on the front and 1.5/2.25 turns in the rear. I also have compression adjustments so I can further tune my car to how I want it to handle. I'm running a 19mm bar on the stiff setting.

So, I'd look at other variables. Trying to tune suspension on the street though won't help much, as grit/dirt (not to mention cold tires) can all play factors that you won't see on the track.


PS - KW setup guidelines is just a starting point. You should be adjusting the shocks for each surface condition.

Quote:
Originally Posted by recce View Post
rear sway bar too stiff.
No, the answer isn't that simple.
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      09-14-2014, 06:59 PM   #4
128Convertibleguy
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Quote:
Originally Posted by cat-like View Post
Hi all. I want to share some experience I have had with my coilovers and see if anyone has had similar or some thoughts on it?

I had KW street comforts installed on my 1er about a year ago now. I also had had the rear subframe bushes changed to urethane and installed Whiteline front & rear sway bars (27mm & 20mm). Changing the rear bar probably goes against the thoughts of some on here but I made the decision to do it based on it was easier to do while the bushes were being done

Anyway, the street comforts were installed with a 25-30mm drop and the shop that installed them set the rebound in the middle front & rear (8 clicks from hard). I found the car handled beautifully and very neutral, this was confirmed at a track day where I was really happy with it. The only slight problem was as a DD, if I was picky the ride was a little too sharp. Maybe the bushings and sway bars contributed to this?

So eventually I softened the rebound by a few clicks to where the ride was very compliant. That created another issue - the back end became looser and slid around more. I experimented with different settings including making the front harder than the rear (which made it even worse) and there is no doubt that the softer the setting on the rear, the more the back end lost traction when taking corners with a reasonable speed. I adjusted the rebound harder (only down to 8 clicks from hard) and the more I made the setting harder, the better it stuck to the road. I found that making the front a couple of clicks softer than the rear created a good balance.

This is confusing, because everything I read says that it should be the opposite, especially with a stiffer rear sway bar.

Today, I read the paperwork again that came with my coilovers and I found recommended starting rebound settings that I hadn't noticed before:

Front: 9 clicks from fully hard
Rear: 6 clicks from fully hard

So apparently even KW recommend a harder rebound setting on the rear!

Am I missing something here?
The thing you're missing is that suspension is much more complicated than you think. Everything affects everything else. Generic theories don't work all that well, and most all of them are based on race car suspension, with all kinds of things like camber compensation. Which is why a big rear bar is unnecessary on our cars. I imagine there's some setup where it works, but it's likely just compensating for something else done uniquely. The most sophisticated suspension pros don't go there.

With street suspensions, "different" things happen frequently. Most everyone finds adding just a bigger front bar to our cars reduces understeer.

One fairly simple thing is that sway bars add spring rate on one wheel bumps. If the two front or wheels hit a ridge simultaneously, the bar just pivots. If only one hits, the bar has to twist. That's maybe a factor in your ride issues.

But the big ride issue is this. If you put stiffer springs on your car, and reduce travel by lowering it, the ride will stiffen. It's physically impossible for it not to. More sophisticated damping than stock may mask it somewhat, if it's set up well.

If you want to lower the car there's a price to pay in comfort. If you overdo it, you can mess up the handling, also. No free lunches here, just tradeoffs. The best setup on the track will not be the best setup on the road.

Given equal quality damping, stock springs and ride height will always give the best ride. Just physics. Some people may like the firmer ride of stiffer springs, but that's exactly what you'll get.

Last edited by 128Convertibleguy; 09-14-2014 at 07:06 PM.
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      09-18-2014, 02:10 AM   #5
cat-like
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Thanks for the replies guys.

I like the setting I have now but I didn't understand the logic behind it. I'm not sure I still do, but I guess I should just be happy that it works
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