2009 October

Wet Weekend at Texas World Speedway

David and I were out at Texas Word Speedway this past weekend, running counter clockwise. While Saturday started out dry, rain rolled in about mid-day. While I have run in the rain, both on tracks and autocrossing, this was my first time to stick around though this much rain with conditions changing the way they were.

On Saturday, rain only came through once. Our third session of the day was quite wet. By our fourth session, the track was drying, with about half of it still wet and about half dry. My car is currently on some rather poor tires – the treadwear rating is 400! It takes only a few minutes of track time on a warm, dry day for the tires to get a greasy feel. As a result, for the first two sessions, I had fun with grip for about 5 minutes, then had fun re-learning limits as I continued to drive. The poor tires plus the rapid overheating meant I gave a lot of passing signals, but that’s ok. I also gained a lot of experience learning to control my aggression on track. I tend to brake late and try to carry speed through corners, so I over-drive easily. These tires have forced me to pull back a bit, go back to the basics of “slow in.”

In our third session on Saturday, the first rain session, we were all re-learning our limits. My car was being extremely oversteery, so I went to hot pit to make some setup changes. I softened things up, but the car still slid easily. By our fourth run session, the last of the day, the track was drying. In its part dry, part wet state, my tires did very well. The wet areas were just enough to keep the tires cool, and the dry bits were fast and fun. This was my favorite run session of the day.

On Sunday, the rain came and went, as the day went by. The track stayed damp for most of the day. One of the artifacts of Texas World Speedway being an older track is the surface has been repaired and patched over time. These different surfaces have some, but minimal, effect on a dry day. But in the wit, the traction difference was startling at times. Entering corner 6, I just let the car slide. I felt like I didn’t have a hope of actually having grip unless I went extremely slow, so I just let the car slip. Then, as the car approached the apex, it hit a patch. Suddenly, the front tires had a lot of grip. The back would shoot sideways, until the back hit the patch, and suddenly it flipped back behind the front. At first, I didn’t quite understand what was going on and it concerned me. Once I realized what was happening, I had fun with it. I’d let the car drift heavily through the turn in, and the car slipped hard then snick back in behind itself quite suddenly. As this happened, I’d smile at the corner workers, who’d smile and wave back at me. ¬†They knew just what I was doing.

All-in-all, it was a challenging weekend, but a fun one.

Street Tires vs. “Slicks”

As autocrossers, we have a number of choices to make. While the novice autocrosser generally starts with the car they have, an early consideration is tires. Tires are a relatively easy part to change, so upgrading to “slicks” may appeal as a way to improve your car and gain time early on. Yes, I say “slicks” – the tires I’m referring to are R-compound (racing) tires that have almost no tread. These tires are DOT approved, and because of that they have two thin lines that are the “tread” of the tires. They’re not true slicks because of those two lines, but they’re near-slicks. Two popular choices are the Hoosier A6 and Kumho V710. While these tires are DOT approved, they are not necessarily street legal. State laws may render the tires not road legal in your area.

R- compound tires provide significantly more grip than street tires, so they seem like an easy way to pick up some extra time. However, they have significant disadvantages for the novice. The most obvious disadvantage is cost. R-compounds wear quickly and frequently cost more than street legal tires for the same car. Still, for the beginning autocrosser, the more significant disadvantages relate to learning opportunities. Street tires provide a more forgiving basis for pushing the traction limits. When pushed, street tires make noise. A street tire being pushed will give a screeching sound, and when that tire is pushed beyond its limit, the sound will change. A grippier tire will make less noise than one with less grip, and the super-grippy near slick R-compounds will almost never make any noise at all. This auditory feedback can be a great tool for helping a driver learn to feel when a tire is losing grip.

Street tires are also more forgiving near their limits than R-compound tires. They’ll start to provide feedback about traction limits (both auditory and otherwise) while further from their limits. Additionally, when they lose grip, the change is less harsh so it’s easier to recover.

Sticking to street tires for a while will allow the new autocrosser a chance to learn great car control skills while keeping costs lower. The times may be slower than they would be on slicks, but learning on street tires will mean the autocrosser will be able to make better use of the more expensive tires if they later chose to switch.

By equiraptor on 8 October 2009 | Autocrossing | A comment?
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