Help with understeering
 

Hello! I have a 2005 AP2 mostly used for the track/HPDE. Before installing my Battle Aero Kit I had a little of understeer which was manageable. After installing the aero kit I got 2.5 seconds faster, but also have a lot more of understeer. My original camber was 3.2 rear and 2.7 front. I adjusted front camber to 3.2 and it got a little better. Then I installed front roll center adjusters and readjusted the front height to 1/4" lower than before and set front camber to 4 degrees and front is pushing more. I played with the dampening and no change. I played with the rear wing by taking downforce and front was still pushing and the rear was very loose, so put it back where it was originally. I tried a square setup and it got a little better, but not a whole lot. Can someone point me in the right direction?

Below is my setup
17x8 +45 Front
17X9 +45 Rear
225/45/17 Front
255/40/17 Rear
TEIN Coilovers
1" drop front and rear
Hardrace Front RCAs
Battle Aero Front Splitter
Battle Aero Rear Wing
Everything else is stock

What are your spring rates and toe alignment? Granted I don't run aero on my car so I can't necessarily give you any meaningful input but I think others who can would like to know as well. Anecdotally several locals to me run 255 nonstagger with the big karcepts bar and rear wing with no front splitter and have no problems but different drivers have different preferences and different tracks have different needs.

@ Shift9303 ,

Spring rates are 10k F&R
TOE FRONT - LEFT .03°, RIGHT .01°
TOE REAR - LEFT .O5°, RIGHT. 07°

Your spring rates seem pretty typical for a dual duty setup. Though most people with aero do run a decent bit stiffer.

Again my car is non aero but I would start by zeroing out your front toe. It's rather small but your current front toe-in (positive total toe) can reduce the car's eagerness to turn in and cause some understeer. 0.04* total toe in doesn't seem like much to me and my DIY alignments are probably within that margin of error but I would start at 0 front toe for a baseline. Rear toe I feel gets very personal. I've had people tell me to run near 0 rear toe-in and I have some tell me they run nearly OEM toe. In the end I split the difference and run somewhere in the middle and have been happy. I think I'm at 0.2* total right now. But having lower toe-in at the rear is probably contributing to that feeling of a light rear end in turn in. I imagine that at that low of a setting you might get a little toe out when the car pitches forward in braking and diving into a corner.

I'll also add that tires can make a difference in cornering attitude sometimes. I didn't track RS4s but at autocross they were not up to the task and I understeered a lot with them. Problem pretty much solved itself when I went with RT660s and RE71RS. That said in autocross we tend to over drive the tires much more. People say RS4 are much better track tires. I haven't run RS4s recently at the track (so I can't comment on that) and have been on RE71RS which have remained pretty neutral.

Also I'd like to clarify, are you still stagger or nonstagger? You mention you tried nonstagger but then you posted current specs for staggered.

I guess for reference my setup is currently 255 nonstagger with RE71RS. Non aero as previously mentioned. 10/8k springs. Karcepts front sway bar at 2/2 to 4/4 depending on day and auto X vs track . F/R camber -3.5*/-3.0*. 0 front toe and 0.2* total rear toe-in. Karcepts front bar definitely adds a bit of push to the front where I can feel it load up but I just turn the steering wheel a little bit more and the car responds so I've been happy.

@ Shift9303
i appreciate your feedback. I tried a square setup since a buddy of mine let borrow his wheels with 255s for testing purposes. I did get better front bite, but the car still pushes past the middle of the corner. My problem could be tires, but the car was pushing before the aero was installed and it increased dramatically afterwards. I know that I'm carrying more speed than before and I'm trying to dial it in.

I'll be switching to a square setup soon with 255s, but I want to solve my understeer problem before doing so.

BTW, I've been running RS4S and they are great after the first heat cycle. They last a long time. I go 7/10ths the first lap and all out afterwards. I'm not looking more into being consistent through my sessions that are 20-30 minutes long. I usually get the best lap times towards the end of the sessions.

The glib answer is, of course, too little front tire - too much rear tire. :) Rear wing acerbates the "too much rear tire" issue with even more traction. Possible to dial some out and move some grip forward?

Tires? The Tire Rack tire tests a few months ago showed the RE-71RE tires 1.5 seconds faster on the GingerMan * 2.21 race course than the R-S4 tires. Their tests were run with the BRZ which is even more under powered than the S2000. Throwing $1000 sets of tires at the problem should be a last resort but this is an expensive game to play in. -- Chuck

* GingerMan is my guess as they don't specify the track other than it's in "SW Michigan."

@ Chuck S

Thanks for your feedback.

I did take some rear down force by adjusting the rear wing, but it had little effect towards the front.
I'm planning on going with a square setup in a few weeks and will be taking my S2K to Winning Formula to get it dialed in. Hopefully they'll be able to pinpoint the problem.

I'll be updating this post afterwards.

When are you understeering?
Turn in, mid corner, or turn exit?
Is it on high speed corners or low speed corners? Or both?
Aero really should only change mid to high speed corner balance.
Your mechanical grip dictates low speed balance.
A video would help too if you're not sure.

Maybe time for swaybar,there is a culculator on here available to look at your bias figs.

Hi Chris!

Below is a link to video for better understanding.