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Old 05-14-2003, 10:56 PM   #1
HaLo
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s13 Oversteer or Understeer?

I just did my first auto-x event last weekend and I noticed something that some people would consider weird at first. My car, when at its limits, is understeering at the entry of a corner. Does your cars do that too?

A friend of mine told me it was because of the HICAS. I doubt it. I believe the car naturally understeer at the entry point and oversteers at the exit.

Would I be wrong? What did you guys experience?
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Old 05-14-2003, 11:58 PM   #2
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Well, HICAS attempts to do the exact opposite of what you described, but what you're feeling might be your 'butt accelerometer' interpretation of HICAS doing its job. It steers out at corner entry for turn-in, then steers in through the corner for a more advantageous slip angle.

I would try starting your braking just a smidge later and carrying it just a little bit longer into the corner so the rear is a bit lighter at turn-in.
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Old 05-15-2003, 02:04 AM   #3
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I've never driven a HICAS-equipped car, so I can't comment directly on that, but ...

If you leave your braking too late into corners you will have lots of understeer on turn-in. It's still sometimes hard to overcome the urge to stay on the gas just a little bit longer and brake as late as possible, even though I know I'll push out on corner entry and completely screw up my line.

If you're understeering at turn-in when you're not on the brakes, work with your setup to try to get some initial lift-throttle oversteer or at least rein in the push. If it isn't driver error, experiment with tire pressure and whatever suspension adjustability you have (Halo, you have AGXs, right?) to get the car to react the way you want it to.
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Old 05-15-2003, 08:17 AM   #4
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Many factors come into play:

1. Too quick entry (which was my error) - I was going too fast because I had a hard time keeping my 12 psi boost level at the exit of the corner. Too much lag on my S15 T28. Actually, it's not huge, but VERY noticeable in Auto-X.

2. Bad suspension configuration - my stock configuration is KYB AGX and Ground Control. Springs are 7.5k-4.4k and my AGX were set to 3 and 5.

Basically, I was too quick at the entry. To correct all this, I lowered the boost to 7psi. Very quick response, spools up faster and allows me to brake more. I set my AGX to 3-8. More damping in back = tendency to oversteer. I also tried to brake later.

Evidently, it all went better from that point: the car STILL understeers but it's much less dramatic. And I get to oversteer from the apex on forward.

Do you guys with your setups understeer at the entry?
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Old 05-15-2003, 09:13 AM   #5
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Quote:
Springs are 7.5k-4.4k
Is that KG/MM? If so, that seems like an odd combination. I think your rear springs a re a touch to soft. I would probably run a 5-6kg/mm spring back there.

Do you have adjustable sways?
What were your hot tire pressures all around?
any idea what your alignment specs are?

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Old 05-15-2003, 01:31 PM   #6
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These are the stock ground control springs that come with the kit. I don't like them either. Thinking of getting custom 6k springs for the rear from Ground Control.

I have stock sway bars. Tire pressure (cold) was 40 psi all around. As for alignment specs, I need a alignment.
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Old 05-15-2003, 04:55 PM   #7
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You might have your pressures just a little bit high.

Does the understeer feel more like plowing, or skating? If it feels skaty your pressures may be high.

At my last autocross I figured out that the 40 psi I had in my Azenis was just enough to pull the shoulders up and reduce the contact patch. I dropped to 36.5 psi in the front for my last run and went 0.95 seconds faster, and all of that time was gained by cutting understeer in a double-hairpin section.
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Old 05-16-2003, 01:18 PM   #8
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since you have a harder spring on the fronts.. you have to compensate that by lowering your front tire pressure
thats the only thing i can think of right now
try 30-35 psi for the fronts and >35psi for the rears..
you just have to mess around with your setups
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Old 05-17-2003, 04:13 AM   #9
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Quote:
Originally posted by HaLo
Tire pressure (cold) was 40 psi all around.
Damn! Try somewhere between 30 and 35psi cold... 40 is for daily driving and fuel economy!
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