B8 S4/S5 Suspension Thread

Scott,

It depends on when under/oversteer is occuring, and if you are on/off the throttle.
If you prioritize the problem of understeer (I’m assuming that is the issue, as that is the natural balance of the car), what is the behavior of the car:

  1. On entry - as you are steering the car towards the apex
  2. Mid corner - you are now pointed to the apex, still steering…but car is moving in the direction you intend. The suspension has taken a set and you are fully cornering.
  3. Exiting corner - as you are getting back on the gas, leaving the corner towards the straight

I am going to go out on a limb and suggest that you are experiencing push on entry, and possibly mid corner. Pls confirm. Also, if you are experiencing push mid corner, pls identify if this is on or off power.

Yup, very much familiar with oversteer/understeer and I do throttle steer the car as well on the track.

On this particular track that’s coming up next month, there are a few sections that I want to see if I can tweak the suspension to help with adhesion. There’s elevation changes at corner exits that seems to upset the car (on stock suspension). I have not run that track with the RSS+ coilovers, but I have far less suspension/wheel travel now (I dare say half?).

Here’s the track map:
http://www.fakelag.net/users/d/37068-2/RidgeRacingSchoolTrackGuide-Printable.jpg

video from last year (video starts as I’m going down the straight - and go easy on me for this one - My first track event in over a year and the first time on the RS5 to boot! haha! Not a representation of how I typically drive - so I was driving quite slow):
https://www.youtube.com/watch?v=2jdDIVssAhg

50 seconds in is one key spot that I want to try and tweak for. On the track map, it’s the exit of turn 6 - where the grey dot is where the surface transitions down and that transition upsets the car (as the car needs to change direction and the car lightens - rear gets a bit loose - I really wish the dumb rear wing would stay up for that corner). I run into this issue at the transition between T3 and T4 as well as T13, T14, and T15 (mini/tighter corkscrew-esque). Usually on maintenance throttle or starting to add power (admittedly, I am quite aggressive on the throttle - not in applying it/stabbing the throttle, but I tend to want to give more throttle and use quattro/sport diff to get out of corners - especially tight corners).

I’ll definitely get the hang of how the car behaves on the first session but would like to experiment with the adjustable dampers to see what would make the car happy.

The track also has hard left corners - T6, T11, and T13 (so tough on the front passenger wheel) so perhaps run different settings right to left wheels?

Now after typing all of that out and thinking back on the road course, I really, really, can’t wait to get back out there…

Ah too cool!

Scott, sounds like your issue may be better aleviated with an alignment change rather than a shock setting change.
You’re talking about at 50+ seconds in the video, where you begin to go down hill and you hit a right corner? Assuming that’s it, and I know you know this, but staying on power is going to stabilize the back end. However, if the car is still being upset by the bump in the road, there are a couple things you can try:

  1. Reduce rear compression. This will reduce bump stiffness in the back and keep it more planted. If this is not possible, then see #2.

  2. Increase rear rebound (this assumes rebound can be adjusted with little to no cross talk/affect on compression settings). This will stop the wheel from bounding back into the road too suddenly, causing a loss of traction at the speed and vehicle loadings you are seeing on that part of the track.

Now if you’re talking about turn 6 as you are cresting the hill, and there is a bump near the exit, the recommendation for the rear remains to be the same. For the front, I would increase rebound.

Try 1 change at a time though and note the difference.

I’d like to know more about what you are feeling the car is doing on entry/mid/exit of a corner (esp a trouble corner–outside of what a surface undulation would do).

That said, I would not setup the left side of the car stiffer than the right side of the car (or vice versa). You’d only do that on a circle track. The thing with a road course is that with funky asymmetric settings like that, it affects the car under braking, over bumps etc. Load transfer happens everywhere, and in a place as technical as a road circuit, you do not want an asymmetric setup.

Personally, I do not see the bump upsetting the car too much in the video–just because it’s likely one of those things that a video cannot capture. But in a transition going from uphill to downhill, you just peg the gas and hold on for life + deal with the rotation that may occur :slight_smile: As you know, keeping the weight transitioned rearward is what you want to do in that situation.

Regardless, those are some smooth hands. Couldn’t say the same for half of the in car videos I happen to come across!
You are dealing with front end traction well in an understeer prone car. You’re also not giving it crazy steering input when it starts to push.

Also, considering that video is from a stock car, you are going to be in for a world of a difference with the RSS. Much better shock platform. If the RS5 OE shock is anything like the S4, it’s got too much bump and not enough rebound. You will have much more rebound control on the RSS. It’s going to be wayyyyyy more stable and consistent the next time you’re out. You’re in for a treat :smiley: Would be good to hear what you think after you come back!

Lol me too that was actually fun to read.

That works for my driving style quite well. The only way to get a 59% nose heavy Audi to have neutral handling is to be in the throttle always. I’m slow in fast out, and getting slow is easy with the Brembo GT-R and the RS5 rears. I’m not big on trail braking, at least not on this platform.

Pilot Sport Cup 2 is showing some interesting wear on the fronts. Not sure which part of my on track driving is causing this (braking or cornering). They’re completely stable up to 50 PSI hot at 160 degrees. PSS get greasy at 44 PSI and become unusable. Running cold temp 28 PSI; hot temp 40 PSI.

http://tapatalk.imageshack.com/v2/15/03/08/85236747491d518da0b834d9fa589e37.jpg

The right side of the pic is the outer edge of the tire right? It doesn’t look like you’re going into the shoulders (or near it).

The inside of the tire (after the first band) looks interesting.

Too much negative camber perhaps?

Do you have access to a pyrometer? It would be great if you could pull off mid session after driving some fast laps and have someone take temps.

Not a lot of rubber pickup.

Looks like the fronts are still being scrubbed (understeer scrub of death!).
Yes, the scrubbing is on the inside. I suspect it’s due to caster.
What tire temps are you getting across the tire? Inside, middle, outer.

How much caster are you running?

Temps are pretty tight. I did have the guy measure with a real probe. For a tire like the Front Left shown, it was 155 156 160 [inside middle outside]. No big surprises. Essentially the recommendation would have been to inflate the tire further but it was already at 48 PSI so that wouldn’t have been possible. Clearly I had to let out 5 PSI.

My buddy with the TT-RS has R888 on the fronts. I would estimate he spent 10% of the lap understeer scrubbing, just holding the wheel off center while the fronts pushed until they hooked up again. Not my personal driving style. His tires far exceeded the OEM TT-RS brakes, which are unforgivably bad.

I’m going to guess that the tire is scrubbing on turn in.
That is, the initial entry point of the corner. It’s possible that you are steering the car while the car is entering slightly hot, so the tire is scrubbing during this phase (understeering). Won’t know for sure without watching a video, but in my mind, it makes sense considering the wear pattern.

The scrubbing is occuring before the car has taken a set, that’s why the wear is all on the inside ribs. It’s possible that you are getting back on the power too early, inducing push.

So I think the wear you’re seeing matches up to the different tread compounds of the PSC2’s. From Tirerack:
“The Pilot Sport Cup 2’s tread molds Michelin’s Bi-Compound technology into an asymmetric design. Bi-Compound technology features different rubber compounds on the tread’s outboard and inboard regions. Massive outboard shoulders feature a tread rubber whose hardness has been specially designed to deliver maximum adherence and outstanding dry grip on curves, especially on tight corners. Notched center ribs and an inboard shoulder use tread rubber featuring a more rigid elastomer to ensure precision steering.”
I’ve also heard or seen the inboard/outboard compounds described as wet/dry compounds respectively, which kind of makes sense now that I see the wear you’re experiencing. Chris Harris also refers to the actually 3-compound design of these tires in his latest GT4 video, check it out! I think the outboard region is closer to an r-comp compound. Michelin has truly made an extreme street tire with this design, its designed to be sold as an OEM tire that has at least some safety margin built-in for the streets and then it’s also capable of setting Nurburgring lap records!

I just picked up a set myself and will be taking them to the track at the beginning of April. I went with the recently released 255/35R19’s with the 96y (XL) load rating, can’t wait to try them!!

Do you run them in the wet at the track too? I’m wondering if I should bring along my PSS street set for wet sessions.

Great observations - thanks for bringing them to light. Good to see the 255 size is on the market, though I have no grip issues with the 235 (which looks like a 245 width to me IRL). I’ll underscore that the PSC2 is what the PSS should have been. I liked my PSS a lot when I had it, but it really gets slippery like a bar of soap if you get it too hot or over 44 PSI. I don’t have a ton of experience on them in the wet so I can’t comment, given the draught in California (0 days of rain in January, for instance). I’m not afraid of wet weather in them.

If I were to upgrade to a dedicated track set, I’d go with Trofeo R in 245/35R19 on set of HRE Flow Formed.

Thanks for the thoughts on PSC2’s. What is your latest cold starting pressure and where do you like to see them end up at hot? I know the PSC’s were finniky regarding pressure but I think the PSC2 is simply different and can’t be compared to PSC1’s (from what I’ve read at least).

Trofeo R’s are definitely high on my list as well as the Porsche guys seem to love them! Then I am also a fan of HRE Flow Formed, check them out in the fog finish: http://www.hrewheels.com/gallery/bmw-m4-with-ff01-in-fog

PSC2 doesn’t seem to care what the pressure is. I got out 28 cold and they get to 40. The first run I started higher and they came off track at 50 hot and I couldn’t tell while driving. They had grip for days. A PSS would have had a melt down.

245 width Trofeo R is simply the pinnacle.

Rear suspension shots: rear 650lb Eibach with helper spring; rear JRZ RS1 damper behind RS5 wave rotor.

http://i57.tinypic.com/2yoa7ae.jpg

http://i61.tinypic.com/2ew1ddz.jpg

West good to see you again. I don’t think I have herd of the helper spring idea. I’m used to seeing the standard spring. Does that helper spring add loft to the drive height or is it ment to be a two spring system.

Helper spring retains the spring at full droop.
It doesn’t affect spring rate, as it is fully compressed when loaded @ ride height.
If you dont have a helper spring with a short race spring, the spring goes loose when the wheel is at full droop.

Here’s the alignment I had done last week. Didn’t go too aggressive with toe to try and keep street tire wear down 8)

https://farm9.staticflickr.com/8732/17137686855_91ba28394d_b.jpg

Looks ideal. Here’s how I’m wearing with about 5000 miles and 8 track days on the Cup 2 which came to me with 5.5mm tread depth from TireRack.

http://i57.tinypic.com/24gjcl1.jpg