You’ll be able to edit when you reach 150 posts.
Also you may need different spring rates for different type of tracks. Some mickey mouse tracks require softer sprung car compared to a track with long duration fast corners like Road America, Watkins Glen etc. I doubt that you can come up with a set that fits all the tracks with different characteristics. On a 1275 lbs Formula Atlantic car our baseline springs front 600 lbs rear 700 lbs. But like the above stated the ratios are completely different than an S4 and the ride height is 1/8 inch off the floor!!
I know this though changing spring rates on a race car cures most of the oversteer or understeer problems. To me S4s biggest problem with stock suspension is the initial weight transfer to rear of the car during acceleration phase of the corner. S4 has tendency to squat down a lot in the rear and causes the front end to get light and cause throttle induced understeer. SO what i am saying is under acceleration the platform of the car needs to be more stabilized, thus the negative rake it creates by squating has to be lessened. HAving said that lowering the ride height and stiffer springs in the rear can help the driver to accelerate at the apex harder.
To add to that comment - the corner exit phase is a real issue with the weight transfer–agreed. The sport diff helps in most situations, but there are some high loading scenarios where the weight transfer is too great and the car will push on exit. I have experienced this at a local circuit.
More than that though, (and perhaps this is due to my preferred driving style), the car plows on corner entry. It’s 100% a “slow in, fast out” sort of car, which is frustrating for me. Even trail braking isn’t helpful due to all the intertia in the front end. It just likes to plow. I will be fixing this with alignment and some parts. I’ll report back when I do 
Circling back to my OP, I have three choices:
- 650 pound rear
- 750 pound rear
- Do not buy this suspension
What does everyone vote? I do favor the longer sweeping tracks like Laguna, Sears Point, Thunderhill. You won’t really find me at something narrow like a Buttonwillow or Willow Springs.
I vote not to go that hard on the rear on such high speed, sweeping tracks. Doesn’t make sense to me.
But again, you have yet to identify just what it is that you were looking to correct from a handling perspective with these spring rates. Either way though, 500f/650r doesnt sound right to me–esp at laguna.
What do you have now, and what’s driving you towards making such a significant upgrade, and drastic change in spring rate? Surely it must be something!
Boro,
I am rocking these springs on my RSS+ H&R setup now and I was curious why you wouldn’t run them. I am not familiar with suspension to any detail.
Is the rate too high or too low? Unbalanced? Wrong distribution?
What I meant to say was that those rates don’t work for my preferred driving style. Nothing wrong with the rates. With that sort of a setup, the car would be improved (more responsive) over stock on corner entry, and yet have a lot of mid corner bite on exit–under power. However, those rates won’t do much for off power rotation.
My preference is to dive into a corner via trail braking, get the car rotated for a late apex, point the car towards the exit and roll into the throttle. With a rear end that soft, it wouldn’t work so well with that kind of driving style. (Though of course, it can be fixed with a big rear bar–though to my knowledge, there is no big rear bar for our cars…largest is 25.5mm).
Once you start to change suspension geometry (I’d say wheel spacers indirectly do this) then of course everything gets more complex. I think Ackerman change would be minor with track width variation, especially when you’re driving fast and not taking low radius turns. Maybe it affects things when turning at low speed in a parking lot, but that’s another issue. Also, definitely running square setup with at most 5mm variation of offset F vs R.
I think the biggest affect would be on roll geometry, and your steering system - mostly self aligning torque since you are changing the scrub radius a lot (possibly changing sign). This is one of the reasons I believe many people are having issues with the EPS system on stock suspension…I guesstimate it becomes a non-issue when you increase the track width with spacers or low offset wheels.
My question was more to how this would affect the “wheel rates” since now, as you said, the wheel will generate a larger moment arm on via the “suspension geometry” under jounce.
I really want to run the JRZ damper. I perceive it to be of extremely high quality.
The OEM struts are starting to lose their tightness after 37k miles, 4 years, and a lot of track time. I don’t mind the slowness of the weight transfer now, but as a driver I could accommodate quicker transitions having gotten comfortable with the chassis. The car is pretty 4x4 at rest but in all of the action shots with the throttle-on, the car is nice and tucked on the suspension.
Good call - Cannot believe I forgot about scrub radius That is huge.
But to answer your question, yes, offset affects motion ratio. Albielt minimally, so in most cases, you don’t need to worry about it…unless we’re talking ridiculously wide wheels and much more negative offset when compared to stock.
To put it into context, the steps to calculate motion ratio requires taking height changes at the center of the contact patch. The contact patch center will vary mildly with different offsets, so there will be a small affect on motion ratio. In general, the difference is so minimal it does not matter–unless you’re talking wide body flares on a car with stock suspension pickup points. Then you have a problem (see RWB porsches–I have beef with them!).
westwest, I wouldn’t sweat the spring rates.
If you absolutely are dead set on getting the JRZ dampers, then by all means get them. A better shock is going to have less shaft stiction than a lower quality one, and the onset of shock fade will take longer to occur. However, you have identified neither of these things to be issues with the current setup, so I wonder if making the move is more excessive than necessary.
I’ve previously run PSS10’s with great success, and I love bilstein dampers a lot since that experience. They are leaps and bounds ahead of Koni, Yokico, Tein etc etc etc. I guess my point is, do you really need JRZ when there are other great options, and cheaper options out there.
Also, being a coil over, you have the luxury of swapping out springs to your liking. Coil over springs are so inexpensive that it is not a huge deal (though to re-align, re corner balance etc is a pain, and costly!). If you want a good baseline to go off of, I’d stick with rates more closely aligned with the PSS or RSS coilovers. You can tune out the remainder of the handling balance with your swaybars and alignment. Both the PSS and RSS numbers look good for the circuits you’ve identified. Putting 650/700 on the back is going to change the car so radically from what you are accustomed to, I truly question if it is a valuable thing to do.
If you are unable to identify what you are looking to improve on power/off power, corner entry/mid corner/corner exit, on brake/off brake…then I’d state that you havent had the opportunity to assess things to that level and digest what would really suit the way you drive at the circuits you frequent. There’s nothing wrong with not knowing. But if you truly do not know, I’d recommend a safe baseline that sticks more closely with the inherint handling characteristics that you are familiar with. Thus my recommendation of being near PSS and RSS rates +/- 50lb/in.
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.
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.
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.
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?
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.
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
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.
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
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.