Another suspension topic - The deal with droop

[Jezza_hr]

Right, I’ve been doing a little bit of research surrounding the optimisation of coilover suspension for the road. For the last few years I’ve been running Driftworks CS2 Coilovers, which for those who don’t know have a bespoke spring set of 8kg/6kg and 16 way adjustment in all dampers. I’ve always liked the setup for its stability and level of adjustment in the dampers, but one thing I’ve never toyed around with is spring preload for droop adjustment.

In recent times, my car has gone back to becoming a daily driver, so it sees more country road action, which for the UK means some very bumpy and pothole covered bits of tarmac that can spell trouble for a lowered car with stiff springs. Due to the discomfort I get from hitting the smallest bumps and potholes even with the dampers on the softest setting, I looked to see if there was anything that could be done to make this a little more bearable.

The first thing I considered was looking into softer springs (6kg/4kg seems to be the preference to many here, so it was my first thought), but upon looking around, a lot of people say it wouldn’t make a noticeable enough difference. Also, after questioning Kam at Driftworks, his response was to sell my CS2s and get a whole other setup to eliminate my issue, as everything about the CS2s is bespoke and works together.

The next thing I looked into was adjusting the droop. There doesn’t seem to be a lot of technical information surrounding this that gave me the information I was after, with the exception of some information on the MX5 forums and on the Driftworks forums, which implied that this could improve the “harshness” of the ride as the shock absorber would not be “topping out”, which is why I’ve come here for more in-depth information.

Out of the box, the manual with the CS2s suggest that the preload on the springs should be set to 0 with just enough ability to move the spring inside its casing with your hands. Now, thinking about this in my head (I tend to work better with diagrams), I could imagine that, should one wheel fall into a pothole, the immediate effect encountered by the wheel hitting the further edge of the potholes on the way up would cause the damper to reach its full extent sooner and more rapidly due to the spring load pushing the damper up as the wheel compresses the spring and damper.

Now, thinking about it differently, if the spring had a negative preload (droop) of say 20mm (leaving a gap of 20mm at the top of the spring when the wheel is at full downward travel), when the same thing happens at the end of that previously mentioned pothole, the wheel would move up 20mm before engaging the spring, which would then in turn push up on the damper allowing an extra 20mm before the damper reaches its fullest extent, meaning you wouldn’t effectively feel the damper “topping out”, or if you did, it would be somewhat softened by the springs compression before it reaches that point.

What I’ve taken away from this is, you’re basically getting the effect of a progressive spring without actually having a progressive spring. The only downfalls being, you will reduce the amount of bump travel (which would be minimal considering the stiffness of the spring, that the negative preload isn’t wound off too far and if the dampers are adjusted accordingly) and you would be having a loose spring at full travel/droop, which is an MOT failure. My next step, should anyone advise this as the best route to take, is look at getting customised helper springs to help with this, as it means that the spring will still be held captive at full travel/droop.

I’m still trying to make logic of this setup and I haven’t ruled out the idea of going back to a standard lowering spring and shock setup, but I think that would defeat the object and it would be nice to try and get more from what I have. Could anybody confirm my thought process or provide any input to help me with my thinking?

Thanks in advance as always.

[totta Crolla]

Don't forget that the weight of the car will compress your 6kg spring by approximately 35-40mm so you still have that much sprung droop before the spring is not captive.
Eibach make a really nice dual spring set up that effectively gives a progressive rate.
http://eibach.com/global/en/motorsport/p...system-ers

[NoHachi]

Wow, few points:

* Your suspension/shock does not typically top out over a pothole. If it does the wheel simply becomes airborne. Full droop is usually reserved for the inside wheels during cornering.

* 20mm of negative preload (spring to short) is not a good thing. NOTHING is controlling the wheel in that part of its stroke, it can accelerate at will to great speed, the spring can rattle, get dislodged etc. Its not a good place to be.

* More droop will not usually cure your comfort problem. The shock needs to allow the wheel to make use of the droop, not something that happens with many of the hugely rebound biased shocks.

* Rebound biased shocks like these typically have a bump travel problem. Don't ask why, but as you hit bad asphalt the car lowers itself and this creates reduced bump clearance. You hit a pothole and its the upstroke that upsets the car as you hit the bumpstop.

* What you want is stroke and as much of it as you can get. That means measuring a few things: how much stroke does the shock have at between full bump and droop?
How much does the spring compress from fully extended to when the car rests on it (no preload)
What is the coilbind height of the spring (in a pinch number of coils x diameter will do.
The trick is getting the car to use the full range of travel and have it resting in the middle of the travel.

* helper springs are a good idea if you need them. Longer, weaker springs are better in your case.

* Doing all of the above usually means raising the car a few cm's, even on shortstroke setups.

* Strongly consider going to a milder tire setup. Going to a 14inch wheel, with 65 series tires (165-70 165-65, those kinds of sizes) on a not to wide rim (max 6.5J) will do wonders for potholed roads. Nothing you do to the suspension will ever come close. Run them at 1.6-1.7 bar. I quite like the feel it gives the car too, very progressive and toss-able.

[Jezza_hr]

(05-27-2014 09:36 PM)NoHachi Wrote:  * Your suspension/shock does not typically top out over a pothole. If it does the wheel simply becomes airborne. Full droop is usually reserved for the inside wheels during cornering.

I was thinking more about the travel after the car comes out of the hole and the spring becoming uncompressed and the suspension reaching back to it's fullest travel. But, my thought process didn't take into consideration the weight of the car restricting the shock from topping out

* 20mm of negative preload (spring to short) is not a good thing. NOTHING is controlling the wheel in that part of its stroke, it can accelerate at will to great speed, the spring can rattle, get dislodged etc. Its not a good place to be.

This was more of a theory when combined with helper springs to decrease harshness, I wasn't intending to opt for a gap in the spring as I would consider it dangerous and my car would fail an MOT. Although I know it's been touched upon having spring gap here: http://www.driftworks.com/forum/chassis-...rrect.html where people have minimal issues

* More droop will not usually cure your comfort problem. The shock needs to allow the wheel to make use of the droop, not something that happens with many of the hugely rebound biased shocks.

* Rebound biased shocks like these typically have a bump travel problem. Don't ask why, but as you hit bad asphalt the car lowers itself and this creates reduced bump clearance. You hit a pothole and its the upstroke that upsets the car as you hit the bumpstop.

So, regardless of whatever I do, I'm going to have the rebound of the shock causing ride harshness and can only resolve this with a different spring and shock setup?

* What you want is stroke and as much of it as you can get. That means measuring a few things: how much stroke does the shock have at between full bump and droop?
How much does the spring compress from fully extended to when the car rests on it (no preload)
What is the coilbind height of the spring (in a pinch number of coils x diameter will do.
The trick is getting the car to use the full range of travel and have it resting in the middle of the travel.

This is where I believe the idea came to mind. Making sure that the car has enough droop to allow the spring to move down when being the outside wheel or lowering into a dip in the road, but enough bump to make sure that when hitting a bump in the road it doesn't bottom out and hit the bump stops. I think this may need some more tinkering to get right, regardless I've never had the car hit the bump stops under any conditions

* helper springs are a good idea if you need them. Longer, weaker springs are better in your case.

This kind of relates to my comment earlier about making sure the spring remains secure

* Doing all of the above usually means raising the car a few cm's, even on shortstroke setups.

Raising the car wouldn't be an issue, but in my case, I think it would be more likely to lower it, as the preload and height adjustment are separate and the height is fairly well set. Removing the 0 preload would only lower the car, unless I put in helper springs, which would likely keep the car at the same height with the right adjustment

* Strongly consider going to a milder tire setup. Going to a 14inch wheel, with 65 series tires (165-70 165-65, those kinds of sizes) on a not to wide rim (max 6.5J) will do wonders for potholed roads. Nothing you do to the suspension will ever come close. Run them at 1.6-1.7 bar. I quite like the feel it gives the car too, very progressive and toss-able.

I did opt for softer tyres (Toyo Proxes) when moving onto the CS2s. Previously, I had a Cusco setup which was more harsh than the CS2s, but I think it's safe to say that whilst they are great for smooth roads, bumpy roads causes the handling to suffer somewhat. I think that looking at a standard koni or Bilstein/Spring combination could be among my options, unless you have any other opinions? I know you've looked deep into this before NoHachi, so your opinions are highly welcome

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(05-27-2014 09:21 PM)totta Crolla Wrote:  Don't forget that the weight of the car will compress your 6kg spring by approximately 35-40mm so you still have that much sprung droop before the spring is not captive.
Eibach make a really nice dual spring set up that effectively gives a progressive rate.
http://eibach.com/global/en/motorsport/p...system-ers

Yeah, that's something I had overlooked (as shown in my response to NoHachi). Is Eibach what you've been running mate? If not, what's your best experience on UK roads with the 86?

[jondee86]

From what I have seen, if the coilover is designed to work with
8kg/mm springs, it is unlikely that it will work with significantly softer
springs. There will simply not be enough stroke available to allow
the use of softer springs without regularly hitting the bumpstops.

What this means is that surface irregularities that you could previously
traverse at 100kph without hitting the bumpstops, will have you on
the bumpstops at (say) 80kph. Not a problem if you don't mind driving
a bit slower, or if you are happy taking the odd decent hit from that
dip you didn't see coming

Cheers... jondee86

[Bean]

not much of a help for you right now, but I ordered the Shockworks coilovers from Australia. Once I receive them I plan to do a suspension video to address how they do - something like this:
https://www.youtube.com/watch?v=_yd2kbU6Srs
I hope I can achieve a better video quality and give more reference points to what's happening (unfortunately no slow motion function on my version of the Contour, 60fps will have to do)

[Jezza_hr]

(05-28-2014 06:37 AM)Bean Bandit Wrote:  not much of a help for you right now, but I ordered the Shockworks coilovers from Australia. Once I receive them I plan to do a suspension video to address how they do - something like this:
https://www.youtube.com/watch?v=_yd2kbU6Srs
I hope I can achieve a better video quality and give more reference points to what's happening (unfortunately no slow motion function on my version of the Contour, 60fps will have to do)

I would be interested in seeing that

[totta Crolla]

I tend to switch my suspension around depending on the type of rally I'm doing and for road rallying I
currently use a Bilstein 300/70 insert ( http://www.gartrac.com/shop/bilstein-lon...00-70.html ) in a custom modified AE86 coilover strut with 12" 280lb springs.
For U.K roads long stroke is best, ok the car does not look that cool but where suspension is concerned there will always be some compromise.
Conventional wisdom suggests that you run the car as soft as you can get away with and tune with anti roll bars.
Talk to the Irish rally lads about bumpy tarmac, you won't get better information anywhere else.

[NoHachi]

(05-28-2014 09:23 AM)totta Crolla Wrote:  For U.K roads long stroke is best, ok the car does not look that cool but where suspension is concerned there will always be some compromise.

Compromise?

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Please note:
Plenty high side walls
Lots and lots of bump stroke.
Reasonable spring rates
Big ass fast reacting Bilstein dampers

*That* is how you build an AE86 that rules the streets. Non of that 8/6 douchebaggery that doesn't work anywhere :-)

Another funny thing I saw in the video that Banpei posted recently, there are N2 AE86s with 6/5 springs. 1.04 round Tsukuba.

For smooth roads you don't need any suspension at all. Think karts.

[totta Crolla]

I said the Irish lads knew best.
Any idea of the suspension spec. of that car ^ and the results it gets ?