I should also add that where the shock digression happens makes a difference.
You don’t want it to be digressive at road race shock velocities, but digressive after. Finding that balance + matching it to your spring rate/car weight and desired handling traits will take time.
Take notes on your lapping days of settings/tire pressures/handling traits. You will refine as you go!
Looking forward to it. I’m on track this Saturday and Sunday at Thunderhill. I’ve done thousands of laps of the 3 mile circuit, and about 100 laps of the new 2 mile circuit. This weekend we’re linking them up for a 5 mile course.
Normally I like to do one mod at a time, but this go around we have new brakes and new suspension. Same alignment as in previous years. I also don’t have a ton of time on the Pilot Sport Cup 2 but it’s been VERY predictable and a logical extension of the Pilot Super Sport - just slightly more heat and pressure tolerant.
I imagine I’ll have my stability program on for Saturday if not the entire weekend. Depends on how confident the car is. I’ll find some open track and experiment a bit if I can. The weather looks great - 63 F and 40 overnight low. The engine will love it, but there isn’t much daylight and the late afternoon sessions are like night - the road surface really cools off and the tires don’t grip as well.
Will post up some GoPro. The lap times won’t make any sense since it’s a new course layout. They’re something agonizing like 3 and a half minutes (2 minutes 5 seconds, plus 90 seconds if you add up the two circuits and assume slow elbow transitions).
I did notice that the JRZ graph has a much steeper ramp to resistance than OEM, achieving 25 pounds of compression at 0.2 in/sec instead of 0.3 in/sec; 25 pounds of rebound at 0.5 in/sec instead of 0.7 in/sec. It’s a steep obtuse angle with the JRZ, as opposed to the OE which ramps at an acute angle, well below 45 degrees.
Wait…I remember how I got the numbers now.
It’s from this thread: http://www.a5oc.com/forums/s5-performance-mods/16031-stasis-ohlins-coilovers.html
A vendor was stating stasis ohlins wheel rates were 400lb/in in the rear. So then we can get to work on the wheel rate formula (wheel rate = spring rate * (motion ratio)^2).
400 = 1100X^2
X^2=400/1100
X^2=.3636
X=Square Root .3636
X=0.6
This is all ASSUMING the vendor’s quote of 400lbs/in at the wheel is true.
So west, you are right. My numbers are not absolute. I have no idea, but I got these #s from the best info I could dig up.
Though if stasis claims and has measured 0.8, I still question it. But honestly I am doubtful. Just look at the spring location.
To measure wheel rate, you measure the change in distance between upper and lower spring perches with each 1 inch of compression. NOT the shock body (contrary to their quote). Notice on the B8, the spring is placed in a seperate location from the shock. If they measured 0.8 at the shock–that is NOT the motion ratio.
Paging west. Looking for update on how the car feels now that you’ve done a few lapping days with the new setup!
Ran it pretty well close to full soft on track (0/24 clicks front, 4/24 clicks rear). Recall that the spring rate is 500 front and 650 rear. It was everything I could have hoped for. The tires had extreme contact with the road - I credit the rebound bias. There was no tendency for the car to snap or do anything unpredictable. I’m probably about 10mm lower than the stock setup I had which was low compared to some people’s OE deliveries. I don’t know if it’s the suspension helping, but my rears are actually doing braking now and getting up to full temp (750F standing) doing so.
In short, I’m not changing anything. I’d recommend JRZ to anyone.
So to play devils advocate, what’s the point of spending all this money only to run at 0/24 and 4/24. Wouldn’t you want to run something harsh at the track and then dial it back for the street. Are these dampers really correct for this application? Do they have something with less damping?
Thanks and all this is a very interesting read. I never thought to much for suspension and I always felt I had the best conditions suspension wise in my S4. It has had low mileage and the suspension has kept very tight. I find myself worried about needing to replace parts as I don’t want to get too far away from the stiff but still suitable setting my b6 S4 has.
Thanks for the pictures. If you say what the 3.0 A4 has you would laugh. It’s flimsy
Those dampers fit on a number of platforms and applications. I think it’s a misconception that the adjustability of coilover systems is for mixed duty. To me, there is a correct setting for your chassis. It’s not like a PASM where it’s going to have an instantaneously variable reaction to localized conditions.
In particular, I’ve shrunk unsprung weight per corner by over 20 pounds (forged calipers, 2 piece rotors, tires, wheels, aluminum damper bodies, etc.) It doesn’t seem to require extreme settings to get the wheel to contact the road.
If you had an M3 with 800/1100 springs, 2" of suspension travel when the car is raised, etc. that might take a more aggressive setting like 16/24.
My point is also maybe what you really want is -6/24, which doesn’t exist on these dampers. So maybe you chose a damper with too much stiffness for your application?
Pretty much what I’m saying is you want to use newton’s method to find a solution (whatever metric you’ve decided represents ‘best’ handling), but you are forced to go with the min value because that’s the extent of your choice. Hopefully that analogy makes sense.
http://upload.wikimedia.org/wikipedia/commons/e/e0/NewtonIteration_Ani.gif
IIRC those JRZ’s are rebound adjustable only.
The settings will vary from track to track, depending on how particular west is about the car’s behavior.
Setup can alter turn in response, mid corner balance and stability under braking.
West is finding that this setup is miles ahead of what the OEM could ever offer - so much so that even in his mild setting he is finding increased traction at the rear under braking (which is expected btw–due to the much greater rebound).
I suspect he will alter the setup if he’s as hardcore as I think he is!
But perhaps in general, if one isn’t chasing after time (laptime), then one likely isn’t going to fiddle much. I would expect that the more comfortable one gets with the suspension, the more aggressive they would become with setup. West’s alignment + rebound is not yet too aggressive. Though for certain, a coilover of this calibre is already outstanding enough at 0/0. His mind is still probably blown at the dramatic difference from stock. Once the brain becomes to reassemble, he may sing a different tune hahaha. I know I certainly do!
I don’t think I need a negative setting. If I were to fiddle with it again, I’d do 4/24 up front and 6/24 rear. The thing I’m optimizing for when I make adjustments is not having passengers notice. Maybe this is the sought after Dinan “performance without compromise”. I’ll ask my brother or my lady if they think the car rides overly harsh or feels uncomfortable. As a road course guy I want the smoothness anyway. I don’t want to clip a curb and have the car oscillate out of sorts.
I’ll get to thrash it again at Laguna Seca on March 7-8, which is my favorite track by a wide margin. I’ll try to keep more detailed notes about the response in particular turns. Particularly, 2, 6 and 9.
New control arm bushings, if you have the 034 kit. I’ll have to try these.
^Yup, you can also get SPC arms with sphericals in them.
Same with the STERN ones.
From what I feel in my fully stock rubber bushing car though, the biggest limiter is the factory LCA bushings. They are huge, and VERY soft. There is so much play under braking that you can feel the whole knuckle assembly deflect under the force as you come to a stop.
I took care of that on the lower link:
http://farm9.staticflickr.com/8341/8288198944_3df30df2a7.jpg
And the lower control arm:
http://farm9.staticflickr.com/8084/8287140315_f06e09ab09.jpg
There are the bushings I’m missing (on the upper right):
http://farm9.staticflickr.com/8216/8287140055_de6ebfd9e3.jpg
Hold the presses!!!
I was looking at my rear suspension today and noticed something I had not noticed before!
The rear motion ratio is closer to 0.9–just like a macpherson strut.
The rear spring acts directly on the same pickup point as the knuckle. This means that as the knuckle moves up and down, the movement for the spring perch will be very nearly the same.
In the image above, you can see that the lower spring perch is sitting on what looks like a lower arm. Actually, this is not an arm at all. Notice that the spring perch is directly connected to the knuckle–the knuckle is actually extended inwards to be the lower spring perch! There is only 1 pivot point here–this is the outer most pivot point on the knuckle. AKA, this suspension is directly acting on the pick up point. This makes the motion ratio much closer to 1:1. (Read: the back end of the B8 is geometrically stiff by design). This means that you do not actually need a spring rate that is sky high for the back of this car (unlike a typical multi-link rear suspension would).
The information on spring rate/wheel rate I had obtained from a Stasis vendor was incorrect, thus making my original motion ratio calculations wrong. In reality, the rear motion ratio is more like 0.9, and the front remains to be around 0.65.
This explains why a more “track” worthy coilover like the H&R RSS has rates such as 690f, 380r. When you factor in the motion ratios, the resulting wheel rates end up being 291f/380r–the resulting wheel rates makes way more sense for this platform.
I really have no issue with the rear being 650 on my car, but I don’t sit in back. I suppose I could go from 500 to 750 up front.
OK I thought you went 1100 or something crazy in the back for some reason!
Just keep the rear compression settings low.
Your wheel rates are 211f, 526r. FWIW my wheel rates will be 195f, 195r (via kw street comforts).
Would make for a lot of good off-power rotation which this car never had. Just always be ready to get back on the power 
especially on those downhills!
If you were going to change a spring, it’d be more beicial to swap the rear than the front at this point.
It really depends on what you are experiencing when driving the car. Such as, how early you can put the power down. Though, I’d argue that if a car is loose on entry, you can get on power sooner to stabilize the rotation ('cause awd!). So this setup still works–depends on your driving style. I noticed no issues from watching your video(s).
That said, the motion ratios also explain why Psychotik likes his RSS so much - they are actually a very balanced setup. (as is the PSS10)
Great info!
And yes, I do love my coilovers. I need to start to experiment with the adjustable dampening. Any guidance on what to do if I’m trying to correct for under/oversteer (since it will differ from track to track)?
Thanks!