Autocrossers - Alignment Discussion...

[Irid]

I'm interested in what setups people are running for autocrossing. Please identify if you are in an ACR or not ;-)

I'm about to realign the car from stockish (been slacking on doing this) because my competition just stepped up their game at a recent event and I know I must do so to compete. I run a 99 ACR, currently with -.4 degrees neg camber all around, RA1's, unknown toe and castor, and 28PSI hot pressure. This is what I run on the street and really all I've done is to play with pressures over the past few events, settling at 28PSI. Shocks are two clicks from full soft in bump all around, and three up from full soft in rebound in the rear.

At the moment the car is neutral in transitions and above about 50mph, but plows in slow corners. I'm planning on upping the front grip and backing off the rear transient roll stiffness (or upping the front) via the shocks which should reduce the understeer in the tight sections without making it too snappy in transitions and at higher speeds.

I was going to bump up to a 305 hoosier up front (I have an 11" wheel), 335 in back and reset to a baseline alignment of -1.75 camber, 1/8th toe in per side, the high spec for castor front, and -1.25 camber, 1/8th toe in per side rear.

This car is daily driven, so the alignment spec is still a bit conservative for flat-out autocross use, but I'd like to hear peoples' experiences with camber above and below that. The non-acr cars won't directly apply to my setup but I'm interested in hearing about them as data points.

 

[Janni]

Just some quick observations:

1. Your tire pessures are probably REALLY low. The DOT Hoosiers should be around 36. At that pressure - you are losing a lot of turn in feel and edginess with slip angles of the tire.

2. Toe - should be OUT in the front about 1/16 per side, and IN in the rear - about same amount. Doing 1/8 inch per side is WAY too much on your car. Toe OUT in the front helps with turn in - and this is something you NEED when autocrossing a Viper and are already experiencing issues.

3. Camber - usually you go .5 degrees or so more in the front than the rear due to swaybar differences and roll. I would think that -1.75 in the rear would be WAY too much - as you don't have sustained high G corners that will cause that much roll.

I am sure others will chime in - and granted - my experience is more road course - but I didn't do too shabby whenever I autocrossed, either.

 

[Tom F&L GoR]

Under the philosophy that the most loaded tire slips first, to get more vehicle yaw you would increase rear roll stiffness, no? With my front shocks always left full stiff, changing rear shock rebound changes corner entry predictably. But it has been a trade-off between high and low speed; more rotation at low speed means more rotation at high speed. I hope your double adjustable shocks let you work this high-excitement feature away.

Remove brake proportioning valve - more rear brake drag under even moderate deceleration in a non-straight trajectory will initiate rotation. This was my secret weapon in AX, (and it's best to learn the vehicle response at AX speeds before track events.)

I have a well-aged Gen 1, but with 550/800 F/R springs on OEM shocks. Camber of 0.8F, 0.5R. Lots of highway miles shows up as inside tread wear far more in front than rear (can't figure that out yet.)

I've had 1/16 total toe out in front, but to reduce street use tire wear, I've lessened it to "barely" toe out. I'm fudging in the belief that I get just enough rubber bushing preload to the toe out direction, rather than have the tire actually turned out. So far, hasn't seemed to hurt performance. 1/16 total toe in at rear, and lower ride height than OEM.

I've never used RA-1s, but 28psi does seem low. Kuhmos like very high pressures (~40 hot) and most other tires I've used have been mid to high 30's.

 

[Dave's Big Brakes]

Here's mine
-2.0 neg camber front
1/16 toe out

-1.5 neg camber rear
1/8 toe in

Woodhouse adj front bar,custom valved Koni's


ck out picture in VCA Viper mag fall 2004 page 50
This is one Kick A car

This car IS driven daily, 32,000 miles

 

[JohninFL]

anyone autocrossing a gen 3?

I would like to stick to using the stock runflats(since its all local fun stuff) in the 18/19 stock rim combo mode and a track alignment would probably help. (do gen 3's have the removable shims?)

any recommendations for specs on a gen 3 alignment?

any opinions on proper pressure for runflats at autox?

any news on sticky tires in 19" so I can stay in SS class ?

(move to 18's all around takes me out of stock and bumps me to ASP)