Late-Season Race Update, part 1

Round 5

Thunderhill in Reverse

After the interesting experience of racing with a broken rear sway bar, I finally tried making a sway bar adjustment. In stock form the Boxster understeers a bit. Adding negative camber in front, and running a smaller front-to-rear tire width delta, help to make the car more neutral.

If you want to make a neutral car a little less understeery (more oversteer), you have two ways to go with the sway bars. It's counterintuitive if you think that stiffer always means better handling. Relatively speaking, the stiff end of the car will be less compliant in corners and thus will slide across the road rather than squat and allow the outer corner to squat and grip. Again, this all relative; if the car isn't pretty stiff to begin with, body roll will outweigh everything. So, one way to go is to stiffen the rear; this makes the rear stiffer but therefore less compliant, allowing it lose grip sooner. The other way is to soften the front; this makes the front softer and therefore more compliant, meaning that it grips better (assuming it's not too soft).

For Thunderhill, I adjusted the rear sway bar to +1 stiffer. Previously I had always run it at the softer setting. (The front bar has 5 holes which I call -2 to +2 in stiffness, and the rear bar has two holes, which I call softer and stiffer.) My first thought was to soften the front, but my friend Erik suggested that before I lose any stiffness in the suspension I should try stiffening the rear. So I moved the rear bar from the softer setting to the stiffer setting.

Thunderhill in reverse is always a challenge to get used to, because I only run it about once a year. This is second time we've run reverse with the Turn 5 bypass. If you stay close to the left edge of the track at the bypass, you will catch air! I avoided the edge by almost a car width; it makes for a nice photo, but is probably not the best line.

Ed catches air.
photo by Dito Milan, gotbluemilk.com

With an abundance of caution considering that I didn't know how much oversteer to expect out of the sway bar adjustment, I did a 2:15 warming up in the first practice session, and then settled down to the 2:13's in the second practice session. I could definitely feel the difference in handling, and to be honest, I was not totally comfortable with it. I've had the car handling in such a stable form for so long, it was just a little unnerving to have the rear end step out a bit on occasion. It just takes time to get used to it, but in the end it should make car capable of going just a bit faster—if the car is in highly competent hands! There is the risk that in the hands of a chicken the car will be slower, as the driver uses too much caution and tries to avoid all signs of oversteer.

My qualifying session was balked by horrible traffic, and I only got a single clean lap in, at 2:14. But most other drivers probably had the same issues, so it all tends to even out. Qualifying put me 13th on grid, behind JC (Ferrari F430) and Nick (Evo VIII), and ahead of and next to Rick (M3), with Ken (TransAm) and Kevin (Boxster S) in the next row.

After an uneventful start, the field started to spread out. At some point, Cris (911) went into the dirt and lost a few places as several of us passed him. For the bulk of the race, Rick (M3) was close behind me. Our cars have an almost identical power-to-weight ratio, so we tend to run very similar lap times. Rick told me later that towards the end of the race, he could tell I was getting impatient as my tires started to lose their effectiveness; Turn 2 in reverse tends to induce a lot of understeer, and he noticed that I was having a hard time hitting the apex, but wasn't letting up. Which is true, because Rick was close enough that I didn't want to give him a chance of getting a run on me out of Turn 1.

One thing I no longer noticed during the race was the presence of oversteer. I think I'm getting used to it. Two events remain.