Coilovers - Bilstein PSS9 vs. GC Street/School

[propcar]

Due to the common misconception that the spring rate plays the largest role in ride quality of the suspension?

[Eric98Sedan]

As an unrelated side note, I'm also curious as to how so many are so undecided on which suspension to get, but very decided on the spring rates to use.

Okay then - let me ask you point blank: what spring rates would you recommend for use with your coilovers on a 99% city street car (the other 1% is back mountain roads), with an otherwise fresh suspension and top tier tires?

[techno550]

Okay then - let me ask you point blank: what spring rates would you recommend for use with your coilovers on a 99% city street car (the other 1% is back mountain roads), with an otherwise fresh suspension and top tier tires?

670 front, 895 rear. For only street use I'd run them a little higher, no preload, and I might run the dampers a few clicks softer than what comes on the setup sheet.

[Eric98Sedan]

670 front, 895 rear. For only street use I'd run them a little higher, no preload, and I might run the dampers a few clicks softer than what comes on the setup sheet.

I thought you'd say that.

Okay - you mention that you'd run them higher. If I lower my car 1" and can shorten your shock bodies 1" then I've effectively maintained OEM levels of bump travel, so I don't follow your logic.

What difference does ride height make so long as I keep my ride height change within the adjustable range of the shock body?

[E36forever]

670 front, 895 rear.

[Mad Dog 20/20]

670 front, 895 rear. For only street use I'd run them a little higher, no preload, and I might run the dampers a few clicks softer than what comes on the setup sheet.

No rear bar, OE front bar, I assume?

I'd love to test-ride this set-up. I believe you when you and others say it rides "well", . . . but I guess I just don't believe you.

I have driven club race cars (Koni D/A w/ k# rear springs) on smooth suburban streets before, granted w/ solid bushings, etc., etc., but the ride was so incredibly far, light years away, from "well" - it was bone-jarring to say the least.

[Eric98Sedan]

If I do go with the TRMs I won't be ordering the 670/895 springs - that's for sure. I'll give up a little handling for a little comfort.

That said, I'd love to "test" this setup as well.

[Mad Dog 20/20]

These rates are incorrect. As per the Bilstein rep I spoke to, they are 455F(linear) and 570R(progressive)

That sounds about how the PSS9 feels/looks to me. The fronts appear to have a progressive coil, but it looks like the soft portion fully compresses at static ride height - rendering it effectively linear. People make a big deal out of the progressive springs on the PSS9's, but I think the soft portions acts as tender/helper springs f/r on an otherwise linear system. IIRC, the TUV mandates that springs must stay tight in the perches even with the spring perches turned to their lowest setting. So I think they went with beehive prog springs for that purpose.

Somebody please correct me if that makes no sense or they know different.

[jvit27]

QFT

pretty much sums up everything I was going to say.. im also running PSS9's only gripe for me is I wish they could go a little lower

Not that it matters around bfc, but there's a reason quality coilovers are not too slammable.... they determine how low you can go without ruining the geometry.

Wait... what?! Is it going to use this adjuster?

http://www.stangtv.com/news/pri-2010...e-shock-shaft/

Just went on Bilstein's german website, the Clubsport coilover (CSC B16), is listed as coming just as Jvit said, Spring 2012

No pricing information has been released yet. However, I wouldn't be surprised if these come in on the range of $2500-$3000.

http://www.bilstein.de/en-uk/product...clubsport.html

Looks like a true 2-way coilover. I wonder if they'll be equipping it with those helper springs as usually those just make it so there's less space in the wheel well.

http://youtu.be/bEXZTTyn1XI

Unfortunately, the adjusters will be on the bottom. (IIRC this is due to the inverted Bilstein design?) Kinda sucks but the flipside is the adjusters themselves look pretty nice.

They do mention they can be setup for Motorsport application so maybe that means spring rates can be specd/interchangeable? When I spoke to the Bilstein rep, they had no data available on what the E36 rates will be... price point should be around $2500 though.

The link you copied is basically the same info as the flyer I grabbed at PRI last month. (Look McCoy - they publish the dyno chart on a product that isn't even for sale yet )



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Before you get too far, add up what the PSS9 shocks, additional linear springs, rear height adjusters and plates cost. Then get on the Vorshlag site and configure a set of 4100s with discounted springs and discounted camber plates cost and see if the difference is enough to put up with the mix-and-match setup vs the full-system approach.

Also, if you are afraid of being too low with no droop, Vorshlag can configure their plates for most struts to give them a little more droop or more height (not both) than their standard setting.

Since you're from Dallas, i'll assume you are locally biased... performance aside, the difference between AST and Bilstein is one has a lifetime warranty AND usually doesn't need it until 100k+ miles.

That sounds about how the PSS9 feels/looks to me. The fronts appear to have a progressive coil, but it looks like the soft portion fully compresses at static ride height - rendering it effectively linear. People make a big deal out of the progressive springs on the PSS9's, but I think the soft portions acts as tender/helper springs f/r on an otherwise linear system. IIRC, the TUV mandates that springs must stay tight in the perches even with the spring perches turned to their lowest setting. So I think they went with beehive prog springs for that purpose.

Somebody please correct me if that makes no sense or they know different.

I was surprised to learn it too, but it makes sense since PSS9 are TUV approved. KW are as well, but they use separate helper springs.
Beehive springs are good because they allow for more travel (definitely helps on a progressive rate)

It also seems these new B16 clubsports match some of the KW features (coated shock bodies and special threads to prevent getting jammed up in addition to the warranty). They sound very promising to me!

[propcar]

No rear bar, OE front bar, I assume?

I'd love to test-ride this set-up. I believe you when you and others say it rides "well", . . . but I guess I just don't believe you.

I have driven club race cars (Koni D/A w/ k# rear springs) on smooth suburban streets before, granted w/ solid bushings, etc., etc., but the ride was so incredibly far, light years away, from "well" - it was bone-jarring to say the least.

I got a short ride in a E36 with TRM's 670/895 rates. 35 series tires on 18s, dampers set full soft and ride height was definitely very low. I'll keep it short, I was suprised with how the car felt. Granted I didn't drive it and ddint get to test all kinds of bumps etc., but definitely not anywhere near bone jarring.

Surely says something about how the valving has been carefully calculated, the engineering, and the R&D that's gone into these. I also haven't seen another damper kit that's recommended to run with those spring rates on the street, and definitely not in the same price range.

I hope to get some in my hands (and on the car) sometime soon. Post up a review/impressions thread.

[techno550]

I thought you'd say that.

Okay - you mention that you'd run them higher. If I lower my car 1" and can shorten your shock bodies 1" then I've effectively maintained OEM levels of bump travel, so I don't follow your logic.

What difference does ride height make so long as I keep my ride height change within the adjustable range of the shock body?

I run them higher because "city streets" tend to have a need for more ride height for front splitter clearance. It has nothing to do with wheel travel. In fact, wheel travel also is not directly related to comfort either. Another common misconception.

No rear bar, OE front bar, I assume?

I'd love to test-ride this set-up. I believe you when you and others say it rides "well", . . . but I guess I just don't believe you.

I have driven club race cars (Koni D/A w/ k# rear springs) on smooth suburban streets before, granted w/ solid bushings, etc., etc., but the ride was so incredibly far, light years away, from "well" - it was bone-jarring to say the least.

Would you believe others if they said JRZs rode well on these rates? Moton? AST? Ohlins? Penske?

If I do go with the TRMs I won't be ordering the 670/895 springs - that's for sure. I'll give up a little handling for a little comfort.

That said, I'd love to "test" this setup as well.

I think the big problem is the general misunderstanding of spring rates and ride quality.

A spring rate change is a wheel rate change. This is a ride frequency change. NOT a ride comfort change.
A lower spring rate is a lower ride frequency. A lower ride frequency is a lower crossover point for transmissibility. For some, the goal is to cross that as quickly as possible. Below that point, transmissibility is > 1, and much higher with lower damping ratios. Because of that issue, OE's run incredibly low ride frequencies, which means the result is a massive amount of wheel travel, and they try to compensate with a TON of preload. The caveat to this is that a much higher damping ratio below that crossover point the lower the transmissibility.
If you want to run a damping ratio of 0.1 or 0.2, you cannot have a high ride frequency on a car that will ever hit bumps at low speed. It will be too rough. You need a MUCH higher damping ratio for ride comfort at low speed.

Too often we run into low speed situations where we here "damper X is too harsh". Is it too harsh? What makes that statement happen? If the user was feeling excessive (or what they feel is excessive) response to the input amplitude, it could be that the input frequency was too low (below sqrt(2) x frequency), the damping was too soft, and thus the bump felt by the chassis/passengers was greater than the bump on the road.


The test would be to find your "harsh bump" as a control, ideally somewhere where you could both measure it (amplitude) and drive over it at different speeds (frequency) and measure the change in perceived ride comfort (transmissibility).

[Eric98Sedan]

I think the big problem is the general misunderstanding of spring rates and ride quality.

A spring rate change is a wheel rate change. This is a ride frequency change. NOT a ride comfort change.
A lower spring rate is a lower ride frequency. A lower ride frequency is a lower crossover point for transmissibility. For some, the goal is to cross that as quickly as possible. Below that point, transmissibility is > 1, and much higher with lower damping ratios. Because of that issue, OE's run incredibly low ride frequencies, which means the result is a massive amount of wheel travel, and they try to compensate with a TON of preload. The caveat to this is that a much higher damping ratio below that crossover point the lower the transmissibility.
If you want to run a damping ratio of 0.1 or 0.2, you cannot have a high ride frequency on a car that will ever hit bumps at low speed. It will be too rough. You need a MUCH higher damping ratio for ride comfort at low speed.

Too often we run into low speed situations where we here "damper X is too harsh". Is it too harsh? What makes that statement happen? If the user was feeling excessive (or what they feel is excessive) response to the input amplitude, it could be that the input frequency was too low (below sqrt(2) x frequency), the damping was too soft, and thus the bump felt by the chassis/passengers was greater than the bump on the road.


The test would be to find your "harsh bump" as a control, ideally somewhere where you could both measure it (amplitude) and drive over it at different speeds (frequency) and measure the change in perceived ride comfort (transmissibility).

I read this about ten times and simply cannot follow you. I'm in over my head with your terminology, but perhaps not the concept.

Take for instance the E46 M3's stock springs and damping. This car has very soft springs (with a ton of preload) and, what I feel to be, "over damped" shocks.

The result is a chassis that moves around a LOT at normal speeds - this makes for a very uncomfortable ride. Not harsh, but not comfortable at all. The handling and chassis control is phenominal at higher speeds, though.

Can you explain my example in your terms? Perhaps a bit of 'context' is what I need.

[techno550]

I read this about ten times and simply cannot follow you. I'm in over my head with your terminology, but perhaps not the concept.

Take for instance the E46 M3's stock springs and damping. This car has very soft springs (with a ton of preload) and, what I feel to be, "over damped" shocks.

The result is a chassis that moves around a LOT at normal speeds - this makes for a very uncomfortable ride. Not harsh, but not comfortable at all. The handling and chassis control is phenominal at higher speeds, though.

Can you explain my example in your terms? Perhaps a bit of 'context' is what I need.

Which terms specifically? The whole lot can be quite confusing.

We have a few terms at play here.
m = mass
C = damping coefficient
k = spring rate

resonant frequency = 1/(2pi) * sqrt(k/m)
damping coefficient for critical damping = Ccrit = 2 * sqrt(k/m)

damping ratio = C/Ccrit


The goal/purpose of the automobile suspension is to reduce the discomfort from unevenness in the road. A measure of discomfort is the vertical acceleration that the passengers are subjected to while in the vehicle.

There are three forces that govern the behavior of the system.
inertia force, damping force, and spring force.
inertia force is m * (d2x/d2t) (2nd derivative of position)
damping force is C * (dx/dt) (first derivative of position)
spring force is k * x.

Road unevenness will be a mix of different bump heights (amplitude) and varying length that can also be hit at different speeds (frequency).

In general, the bumps seen are smaller at higher speeds. (i.e. you generally don't hit really tall bumps at high rates of speed.) If we take this to the extreme, we can idealize the condition as a constant peak velocity and analyze it across a wide range of frequencies.





If we want to look at real world applications, we can use the E46 M3 example. Hell, lets make it even more general than that. Unknown vehicle X. If we assume a constant damping ratio: If it feels harsh at low speed but not at high, lets look at what that likely means. We have *excessive* movement (per the feedback of the people in the car) versus the input velocity. If we assume low speed (vehicle) means low frequency, then we need to determine if this is above or below ride frequency * sqrt(2). If it is below, then the damping ratio may be too low. If it is above, then the damping ratio may be too high.


If we want a more simplistic example of transmissibility, then we go back to the speed bump example. This is a classic example of transmissibility. At extremely low speed (crawl), the car (and thus the passengers) moves up the same height as the speed bump. At a slightly faster pace (walk to fast walk) the car can move up higher than the bump ("jump" over the bump). Faster still and the chassis movement will start to decrease. At 40+ mph, you might bend a wheel, but the chassis won't move as much. You won't "feel" as much of the bump.

With that concept, as damping ratio increases, the "low speed" side of things get smoother (the "jump" over the bump is not as high an overshoot with the chassis), but at high speed, the chassis movement is increased.

If we look at spring rates themselves, they do control how far the chassis moves (dives, rolls, squats, etc), but their effect on ride comfort is not as direct as everyone seems to think. You can take the stock rate and multiply it by 10, and it does not become 10x less comfortable. The ride comfort is chassis movement, and that is transmissibility, and that is damping ratio moreso than ride frequency. Dampers are *that* important.

hope that helps a little

[Eric98Sedan]

The ride comfort is chassis movement, and that is transmissibility, and that is damping ratio moreso than ride frequency. Dampers are *that* important.

Thanks for summing it all up. I'm comfortable with the idea that most of the comfort (or lack of in the 46M's case) comes from the dampers, bushings and tires and not the springs.

I'm having trouble with two things:

1. Please define Damping Ratio in laymen's terms, and
2. If spring rate doesn't affect comfort then why not run 10x the spring rate on the street? (This is a trick question - if you say spring rate does affect comfort then I'll ask why you'd not recommend more 'modest' rates for a pure street car) Of course spring rate does affect chassis movement (I would think moreso at slow vehicle speeds), and thus ride comfort, to some degree - so why the sky high rates? I mean, what's wrong with say a 500/650 set? Will it not be slightly more comfortable yet still handle well?

3. Final question - what spring rates are available with your coilovers that are lower than 670/895?

[KnudsonsM3]

Eric, you should just drive a car with them on lol

Or call him

[techno550]

Thanks for summing it all up. I'm comfortable with the idea that most of the comfort (or lack of in the 46M's case) comes from the dampers, bushings and tires and not the springs.

I'm having trouble with two things:

1. Please define Damping Ratio in laymen's terms, and
2. If spring rate doesn't affect comfort then why not run 10x the spring rate on the street? (This is a trick question - if you say spring rate does affect comfort then I'll ask why you'd not recommend more 'modest' rates for a pure street car) Of course spring rate does affect chassis movement (I would think moreso at slow vehicle speeds), and thus ride comfort, to some degree - so why the sky high rates? I mean, what's wrong with say a 500/650 set? Will it not be slightly more comfortable yet still handle well?

3. Final question - what spring rates are available with your coilovers that are lower than 670/895?

Everything is a trick question... or more precisely, everything is a compromise.

Damping ratio is the ratio between the currently selected damping of the system to critical damping of the system. A critically damped system returns to zero as quickly as possible with no overshoot/oscillation.
Overdamped will return to zero with no overshoot, but slower than critically damped. Underdamped will eventually return to zero, but with overshoot/oscillation. We are generally a good bit underdamped.



Spring rate effects ride frequency. Ride frequency affects the crossover point (sqrt(2) x frequency). Too high (frequency) a crossover point and you have a lot of movement of the platform as your "low speed" (low frequency) stuff is now a wider range.

Note that this effect is the change in ride frequency. Changing the spring rate is not the only way to change the ride frequency. Changing the vehicle mass will also shift the ride frequency of the vehicle. (notice the k/m term in the resonant frequency equation above.)

More spring rate gives us platform control. Ideally we want things as soft as possible to keep the crossover point as low as possible. The catch here is that everyone was WAY too low. Too low for bad reasons too.

If we have another example, lets have a control vehicle of 3000 lb, and stock wheel rates of 100 lb/in front, 120 lb/in rear. We'll denote this "test case E-3.6" just using some random numbers and letters. We'll say the vehicle mass distribution is even, and so 750 lb per corner.
We have a front ride frequency of 1.14 Hz
We have a rear ride frequency of 1.25 Hz

Now lets TRIPLE those spring rates
front of 300 lb/in, rear of 360 lb/in.
We have a front ride frequency of 1.98 Hz
We have a rear ride frequency of 2.17 Hz

Now lets try 6x the spring rates
front of 600 lb/in, rear of 720 lb/in
We have a front ride frequency of 2.80 Hz
We have a rear ride frequency of 3.06 Hz

And keep in mind these are simple ride frequencies, ignoring things like the sway bars.

So we see that the balance is still there, and we moved the ride frequency from ~1hz to ~3hz by going 6x the wheel rate.
Lets assume the motion ratio for the "E-3.6" is 0.94 for the front and 0.65 for the rear.
Now if we convert that 600/720 back to spring rate, we get 600/(0.94*0.94) = 679 for the front and 720/(0.65*0.65) = 1704.

So the springs on that car with that wheel rate, keeping the same balance/split as stock, but 6x the rate, we end up with spring rates of 679 lb/in front, and 1704 lb/in rear.

I see plenty of people get close to this on the front (TRM uses 670 lb/in), but the rear....

We have springs in stock that are 560, 670, 780, 895, and 1007.

[emtres]

was looking into these TRM coilovers,

how is the quality of the internals pistons/shafts, fluids, seals etc? compared to others? I know these are much cheaper than other premium coilovers so how were you guys able to control that much spring... no matter what it's higher than what can be run on Ground Controls/TcKline's singles and I think higher than Double Adjustable koni's too!

How about the adjustability? How precise/repeatable are these in comparrison to PSS9's, or AST's?

How are these able to ride well given the spring rates? Yes I read the explanation above, but I don't think people even with high end coilovers from JRZ/Moton/MCS are using those rates on the street. I saw somebody reviewed the MCS singles and went down to like 300f/400r, and those are supposed to be really nice shocks!

[JCooper]

I'll tell you right now that GC's Street kit will not make one sound. I've been running them for a little more than a year now. Since the camber plates on the street kit have no caster adjustment it dosent have that bearing setup that goes bad and clunks like on the track kits.

[Eddie916]

Good post. I don't think anyone could actually hate the PSS9/10 systems... they're just too good. What people hate are the Billy Sports because of their ultra stiff valving. They feel, to me, like PSS9s cranked to full stiff.

This

[Morpheustj]

I prefer the PSS9's over the GC kits.. I have had them on 2 different cars.. The 325is had helper springs on the front but the set on my E36M3 doesn't. Both were still drivable & trackable.. I'm really curious about the new Clubsport kits the offer.. Has anyone had any experience with it yet? Double adjustable & a ton of setup options..

[HamsM5]

Reviving an old thread because I've been in search of something more compliant than what I have now. I am running a GC street/hybrid setup and the ride is way too harsh. It does get a little bouncy at speed but the impact harshness is just too much. Either that, or I am just getting older. I had Bilstein PSS9's on my E39 M5 and I really liked them. At this point I am willing to sacrifice a little handling for a much more comfortable ride. I've been researching between the KW V2's and the Bilstein PSS9's. My car is all street. I won't ever take it to a track.

Thoughts?

Chris.

[jvit27]

Reviving an old thread because I've been in search of something more compliant than what I have now. I am running a GC street/hybrid setup and the ride is way too harsh. It does get a little bouncy at speed but the impact harshness is just too much. Either that, or I am just getting older. I had Bilstein PSS9's on my E39 M5 and I really liked them. At this point I am willing to sacrifice a little handling for a much more comfortable ride. I've been researching between the KW V2's and the Bilstein PSS9's. My car is all street. I won't ever take it to a track.

Thoughts?

Chris.

http://forums.bimmerforums.com/forum...4#post25149844

I tried to tell you..

Bilstein nailed the PSS9 setup on everything but the E36. The dampers are good, but the spring rates they chose are not. You could get PSS9 and do a linear spring conversion with some 300/400 springs. Would be a great setup but that would put you north of $2000, and within reach of TCK DA Koni's.. so it really depends on what you are willing to spend. TCK really nailed it for street use with their dampers, and compared to a GC Koni it really shows how important valving is.

Do you prefer progressive springs? Is adjustable ride height a priority? What is your budget?

[HamsM5]

http://forums.bimmerforums.com/forum...4#post25149844

I tried to tell you..

Bilstein nailed the PSS9 setup on everything but the E36. The dampers are good, but the spring rates they chose are not. You could get PSS9 and do a linear spring conversion with some 300/400 springs. Would be a great setup but that would put you north of $2000, and within reach of TCK DA Koni's.. so it really depends on what you are willing to spend. TCK really nailed it for street use with their dampers, and compared to a GC Koni it really shows how important valving is.

Do you prefer progressive springs? Is adjustable ride height a priority? What is your budget?

Ride height is a priority - I want to lower the front about 1.5-2.0" and the rear I only wanted .5-.75" drop.

Ride quality is more a priority for me at this point. This car won't see track duty so I don't want to waste time with another ridiculous setup that is too harsh. Like I said- I had the PSS9's on my E39 M5 and the ride was perfection. Just looking to get something similar.

I was looking at the TCK S/A coilovers but honestly I have such a bad taste in my mouth over the ride of the GC's that the TCK's put fear in me. I was really looking for a progressive setup that would be more DD friendly.

Like you said; my car is too nice to turn into a rattle trap.

Chris.

[Br0keMyWallet]

KW V2's seem like a good choice. here's a nice writeup from Motoiq that got me interested in the KW V2s when I was looking around for coilovers - http://www.motoiq.com/MagazineArticl...ompletion.aspx

If I was DD-ing my car I definately feel like I would get KW V2s.

Personally since I am using my M3 more for track and not DDing I got GC Street/School that I can't complain about because I came from old Teins and at the time of purchase TCK was out of stock and I needed them asap.

[jrsmitchell]

Chris do you know what spring rates you have on your GC kit? You could try a softer spring for not too much money, unless you really think the valving is the problem.

Nice car and nice collection