Sunday, September 26, 2010

(119) Skip Barber Advanced Racing School

My advanced racing school in the Skip Barber F2000 went really well, I think.

The first day started off with more autocross sessions. Actually we ended up doing more autocross than the 3-day - we spent all morning dodging cones. Not very manly or dangerous, but it was fun to chuck the car around. I had some pretty large drifts, "large" being a relative term, since formula cars don't have much steering ability and thus can't hold a 90-degree slide like a dedicated drift car with special suspension geometry.

The on-track sessions in the afternoon started with lead-follows behind the Mazda 3s. When you're riding in the Mazda 3, it feels like you're going a lot faster than you actually are, since the car is a lot less capable than a race car (even though it has the same BFG G-force tires on it, which makes the car a lot faster than stock). Following the Mazda in the formula car, you realize how slow you were going before, since it's a breeze to keep up. It's still quite a capable family sedan, though.

 Laguna Seca, how I missed thee.

After the lead-follows were done, and we were re-acquainted with Laguna Seca, we started turn 2 braking drills. I'm still not 100% comfortable with the brakes. I'm getting very close, but getting that perfect threshold pressure every time is a bit hit or miss. At least I'm not locking up any more.

The brake pedal on these cars needs to be felt to believe. My mom tried sitting in the car, and I walked her through getting threshold pressure. I told her "push the brake really hard, until you feel the throttle under your foot" (since the throttle is positioned lower than the brake, so that at threshold pressure the pedals are even with each other and it's easy to blip with heel and toe). She pressed hard, and didn't feel it. I kept telling her to press harder. The harder she pressed, the greater the expression of disbelief on her face. The brakes really are that stiff. After 2 days, my foot was by far the sorest part of my body, which isn't saying much because I wasn't that sore. But even still, I was walking a little funny the next day. All my braking in the kart was done with the left foot. Now I have an even stiffer pedal, and I must use my unconditioned right foot.

I had a few things to fix with my braking, mostly line and timing sort of things, and I made sure to cure them quickly so they didn't become a problem. A session of free lapping ended the first day.

The corkscrew, turn 8. It's quite steep. From here, it's a 300 foot drop down to the bottom of turn 10.

The following day was spent entirely on track. The morning started out foggy, but it cleared up pretty quickly. Standard coastline weather. The order of the day was instructor lapping.

The instructors would get in their race cars and would drive around with us, watching us, showing us, and sometimes passing us for practice. I and another karter were paired up with Lonnie Pechnik, one of the instructors from my 3-day. He spent a lot of time chasing me, and I received a ton of good feedback as a result.

The car I was using was understeering quite a bit. If I had to hazard a guess, I'd say the front ride height was too high, since it took a good bit of effort to rotate it well with the brakes and when I got back on the power the understeer kicked in. This was a problem in the high speed corners, where you are on the throttle from entry to exit to keep the rear end under control. I had to limit my speed through turns 4, 6, 9 and 10 to keep from running off the road due to lack of front grip. Lonnie was having the same problem, and his suggestion to "drive around it", as he put it, was to let the car roll into the corner before applying the throttle.

Normally in the fast corners you need to get on the power before you turn for the corner, that way the weight stays on the rear of the car and it stays stable. If you have understeer problems, you stay off the power and allow more weight to transfer to the front of the car, giving you more front bite and less understeer.

Learning how to tame my turn-in with the throttle rather than the brake is totally new for me.

 Lonnie Pechnik chasing me into turn 11. This car is red, and the other is white, because the pictures with the white car are from the 3-day that I just now got in the mail. I drove this car in the 3-day when the white one had an issue.

In general I was going a lot faster. During the 3-day, I was being fairly conservative. I wanted to really feel the car out. During the 3-day, my lap times were in the 1:45 range, which is a little slow for this car. Now, my best times are in the low 1:41s. Amazing what just a little bravery can do.

So lets see what that bravery did eh?

Advanced school roll bar footage.

The camera is still having issues. I tried stuffing the housing with paper, since the camera was vibrating inside the case itself, but it only helped a little bit and made the audio worse. The next time, I will get some foam to place under the roll bar mount itself. That should take care of it. I also didn't quite tighten the mount all the way, and a couple of bumps knocked it askew.

These two days really reinforced how much more I'm enjoying driving cars. Karts are really fast and exciting, but the car is more satisfying somehow.

There is not a whole lot on the calendar at the moment. Over the next few weeks I'll talk about what is coming up at the end of the year, and what the plan of action will be for next year.

Monday, September 13, 2010

(118) New body

I've had a couple weeks to think about my 3-day school. I've thought about how I did, what I accomplished, and what I still have yet to learn.

In a week, I will go back for my 2-day school and learn even more.

But what am I learning exactly? What's new about this that's so different from karting? In some ways, my new body (the car, that is to say) is very different from the kart in some areas, and not so different at all in others.

For starters, the car has a transmission. It's not so bad, though. The pacing of the car is much slower. That is to say, the length of the braking zones, the length of the straights, the time you spend in the corners, is much more on a big track in a big car. So you don't feel as rushed, and even adding the shifting doesn't make it feel as frantic as the kart.

A lot of that is also due to the suspension. The car needs much calmer inputs just to keep from spinning out. You also have to be more "ahead" of the car. In the kart, if you get a slide, you just flick the steering and it's done. The weight transfers instantly, and it recovers right away. The car is more ponderous. Increased weight, and the addition of springs and dampers means that you have to be a lot more patient, and a lot more "pro-active" with your inputs. For example, in a slide, you can't just flick the steering quickly, then have it all over and done with. You need to get on top of the slide quickly, like the kart, but then it becomes a little bit of a contest. You have to hold the correction long enough for the car's momentum to stop it's rotation, then pre-empt the chassis by bringing the wheel back into line pronto, otherwise the car will snap again in the other direction. No matter how slow you are with the steering, that "tank-slapper" effect just doesn't happen in karts. I've never seen it, and I've never done it.

The other big difference is the way the rear wheels act. In the kart, the rear wheels are joined by a single axle. While this seems proper at first, it presents a physics conundrum. If the car takes a corner, the inside wheel will be covering less distance than the outside wheel. Because the chassis is between the two, the road will be trying to force the inside wheel to move (roll) slower than the chassis, and the outside wheel will be forced to roll faster than the chassis. This creates a rearward dragging effect on the outside edge of the car which will try to pull the nose of the car to the outside, creating understeer when no throttle is used. The solution in the kart is to jack the inside rear wheel up by having a flexible chassis and sheer cornering ability, but when you're using independent suspension in a car, this becomes very hard to do indeed (unless you're one of those short-wheelbase, front-heavy, oddly-shaped-suspension-geometry hatchbacks).

The solution for the car is a differential, which allows the two wheels to roll independently while still enabling power delivery. The basic type of differential is called "open". The wheels have an infinite range of speed difference. The outside wheel could spin at 100 MPH while the inside wheel could spin at 1 MPH and the car wouldn't complain much, and it makes normal turning quite optimal. The problem occurs when you try to get on the power.

The way the open differential has to function means that the wheel which loses traction first gets all the engine torque (it is popular to explain it as "the wheel with the least grip gets the most torque", but that is inaccurate, since the wheel needs to have very little resistance to warrant full torque to only that wheel, which generally means it has to be sliding first - if neither wheel is sliding or spinning, they get pretty much the same torque). This means that, since the car is leaning sideways and "unloading" the inside tire, the inside tire is going to let go first in a slide, at which point it will get most of the torque from the engine, pushing the rear wide and creating oversteer. This means that open-differential cars tend to have less acceleration ability coming off the corner. If the car were to have a "limited slip" differential, a differential whereby the difference in wheel speed is limited, this becomes less of a problem. The inside tire will still let go first, but with a limited slip diff, you can ensure that the outside tire is still getting a decent amount of torque from the engine.

So, at Skip Barber, I've gone from one end of the spectrum to the other. From fused rear wheels, to rear wheels that don't have any limits on how fast they can spin relative to one another. I seem to be doing okay with it, though.