aftermarket custom spring rates for JRZ suspension

B8 S4
#32

I had the PSS9 on my E90 325i and really liked them. But I ultimately landed on the Ground Control setup with the built in camber plates. Affixing Vorshlag camber plates to the PSS9 didn’t really work out as a I planned (it was machined way too low).

I love the B8, and I want the same car but different. If a state of the art damper kit exists, I want to give it a try. By and large I’ll live with the new behavior and adapt my driving to it. The closer to stock the better, in terms of corner entry/apex/exit. I just want to let the damper keep the tire on the tarmac, and allow the suspension to travel a bit to cushion the 3750 pound dry weight.

#33

Given that, I’d highly recommend rates like the PSS10.
Having experienced the B8 with PSS10s on the circuit, I can tell you that handling traits are like stock–only that the limits are much higher, and you can expect greater consistency from the setup.

#34

I had the PSS10’s on my B8 S4.

They utilize the stock rubber top hat bushing, whereas the Ohlins mated straight to the body (metal to metal), not to mention a linear spring rate (vs. progressive Bilstein).

The ohlins were better handling but more rough of a ride (NVH). I wouldn’t get the Bilsteins for pure track duty because of the progressive spring duty alone.

#35

http://img.tapatalk.com/d/14/08/08/uvuze6ur.jpg

http://img.tapatalk.com/d/14/08/08/y3uvy7u6.jpg

http://img.tapatalk.com/d/14/08/08/umezypum.jpg

Don’t know how different or similar this is to the B8 S4 (can’t remember). Should be similar?

#36

I installed my RSS+ and removed the rubber top hat spring isolated you mention. However, over small sharp bumps the car sounds like it is being pulverized up front. Car handles like a dream, but I wonder if I should put the isolators back in to regain some DD traits.

Thoughts?

I do run the struts at full stuff front and rear though.

Boro,

What would typical handling change be associated with softening the rear dampers but leaving the fronts full stiff?

-2 camber front
-1.2 camber rear

Slight toe in front for more aggressive/twitchy turn in. Sway bar soft in front and stiff in rear.

#37

FWIW here’s the alignment I run now:

http://i39.tinypic.com/23uezja.png

#38

Question: Front toe - is it toe in or out? Toe-in will actually make the car less aggressive on corner entry. But you may get better mid corner front end bite once the suspension is loaded (esp if your setup lifts the inside front).

When you’re talking adjusting dampers, are we talking bump or rebound? Two very different things, with two very different end results. I’m assuming you mean rebound.

Increasing front rebound is going to make the car push a lot more. Having the rear with min rebound is going to do the same thing. Rebound = how fast the shock re-extends. With increasing rebound, you are loading the tires much quicker this way, and you will reach grip limits sooner.

Curious to know: how do the RSS ride on the street? I have my eye on those, but dont want anything harsh. I must say, PSS10 on the B8 rides…like stock. So that works :slight_smile:

Westwest - your alignment looks good for high speed tracks. I’d leave it as is, unless you’re looking for mitigate some push. Otherwise, it’s a very safe setup and would be something I’d prefer to run on the circuits you mention.

#39

I have nothing technical to add, but wanted to say that this thread is amazing. I’ve only ever seen these products talked about in stance threads. On AZ, you’d never get this level of quality discussion and technical expertise. I’m learning a lot.

Thanks,
-Skid

#40

On the topic of rebound, I should add that because the shocks extend quicker with more rebound, it means you are transfering weight quicker.

For example, if you increase front rebound and decrease rear rebound, it means the front end of the car wants to rise back to static ride height much quicker than usual. Imagine the car does this during braking, or during cornering… What this translates to is weight shifted rearward more swiftly (or conversely, weight taken away from the front end more quickly), resulting in an increase in rear end grip.

In a road course situation, this causes understeer. In a drag strip situation, this hastens weight transfer to the rear, increasing “dig” and traction off the line.

#41

I learned quite a bit more reading through some of these posts: http://dreamingin302ci.blogspot.com/

#42

Read post #35.

The RSS+ are single adjustable, so it adjusts rebound and compression all in one.

They are a bit harsh but my inquiry in post 35 may alleviate some of the harshness, was looking for some input regarding this issue.

#43

It will help with noise and vibration, not harshness.

#44

Confused :slight_smile:
My response was to post 35 :wink:
I was answering the inquiry about shock setup. Which, in general, even if the shock is single adjustable (rebound + compression in one), rebound moves up incrementally more than compression would. Most properly done shocks are nice this–and since the RSS uses a Bilstein strut, it most likely works the same way. With that in mind, my original response will still be relevant to your inquiry.

Regarding the top hat - are you referring to the actual strut mount, or the spring pad?
If it’s the spring pad, I would not remove that.
If it’s regarding the actual tophat for the strut, you have the option of substituting the stock one for the one that came with the RSS (assuming shock shaft diameter is the same–which if they’re like the Bilstein struts, they should be!). I would definitely retain the stock top hat for street use.

Plus, since the front end is double wishbone, having a firmer top hat won’t do nearly as much for performance as it otherwise would on a mac strut car (as the top hat would directly affect keeping the wheel’s alignment under load).

#45

Yes, basically I was referencing the first part of the post.

I am referring to the rubber spring isolator that sits between the hat on the spring. I will put it back in and let you know how it affects the ride.

Thank you very much for the response regarding my dampening question.

#46

If you just think about the front end of the car only to keep things simpler this is the effect of bump and rebound

Too much front bump: stiffer front feel car will have minimal nose dive under breaking.
Too little front bump: softer front feel car will nose dive heavily under breaking and will have lot more roll in the corners.

Too much rebound in the front car under breaking will come back from the nose dive lot quicker to its original platform
Too little rebound under braking in the front car will stay nose dived for a long time i am not saying for a day but it will feel like you are doing an endo on a bike especially if you have the bump on soft setting. That also causes the rear tires to get lighter and may even cause rears to lock up.

Lets go to rear now and think about acceleration

Too much bump in the rear under acceleration, car wont squat since its way too stiff, the weight stays more to the front of the car. I think this is what s4 needs personally.
Too little bump in the rear under acceleration car will squat really good tranfering all the weight to the rear and may cause the front get lighter under heavy accell there fore causing corner exit throttle induce understeer which i think S4 suffers from.

Too much rebound in the rear under acceleration keeps the weight transfer to the front more, even the small squatting gets back to normal immediately, meaning car keeps it pre acceleration platform
Too little rebound in the rear car will squat under acceleration heavily especially if this compunds with soft bump settings in the rear. Ass of the car will stay down longer. In a corner this helps eliminating you shitting your pants with massive throttle induced over steer but with that may come nasty understeer.

I hope this helps explaining bump and rebound in a nut shell.

#47

Figured I would share this picture of the RSS+ front springs confirming the 686 lb/in rate.

180 is uncompressed spring length
60 is external diameter(don’t quote me)
120 is N/mm which converts to 686lb/in

http://tapatalk.imageshack.com/v2/14/08/22/b644d552bae66eed3185b83151e1c677.jpg

#48

Awesome!
Not bad. IIRC the rear was in the 340lb range.
Do you know if the RSS are adjustable? If so, I personally would be tempted to swap out the rear springs for something else. How are you liking them after putting back the spring isolator?

#49

Correct the rear spring is 60 N/mm so half of the fronts exactly.

I am noticing less NVH after putting the front spring isolators back in. Really enjoying the setup right now. Front dampers are 3 from full stiff, and the rears are set to full stiff.

Really good neutral leaning to oversteer setup right now.

Sway bar soft in the front and full stiff in the rear.

#50

Nice! I’ll be installing mine next week. It finally arrived from Germany…

#51

Placed an order for the JRZ kit. It’s kind of complicated. Order from a shop in CA that calls a shop in MD that calls the Netherlands. I wish there was like an Internet of computers that could do this.