Tuesday, May 3, 2011

Track Day Driving Techniques

High-Speed Straights and Sweepers

Autocross courses are great places to find the limits of your car. In particular, most courses will include at least one high-speed sweeper. On these corners, you’ll want to get your car right at the edge of adhesion. You’ll be able to tell where that is by the squeal that the tires make as they struggle to hold on. You’ll often hear the saying, “A squealing tire is a happy tire,” but you won’t know what that means until you turn your car into that long curve then push down on the throttle until the car is right at its limits, using the throttle as much as the steering wheel to keep the car on course.

Gear selection and shifting is one of the few driving techniques that you probably won’t get to practice much when you’re autocrossing. Because most courses are so short and tight, you’ll probably find that you start in first, shift up into second as quickly as possible, and then stay in second gear for the entire course.
Occasionally an event may be able to set a course that does include one or perhaps two very long straight sections, where an upshift into third is needed towards the end to keep on the power band or avoid exceeding the rev limits. Even on these courses, you’ll need to downshift again almost immediately to be ready to power through the next corner, so you won’t lose much if you just run the car up to the top of the rev range without shifting.

Starts and Finishes

Nearly all autocross courses are timed electronically, with a beam of light and electric eye at the start and at the finish. As you make your start and cross the finish, your car breaks the beam of light, starting and stopping the timer.
For safety purposes, the SCCA has had a long-standing rule that there must be a right-angle turn before the start line, and another right-angle turn before the finish line. The cones that mark the turn before the start line, and after the finish line count just as much any other cone on the course, so you have to be careful in your start and finish. These rules help assure that cars don’t enter the course or leave the course at unsafe rates of speed.
The most obvious tip is that you want to be going as fast as possible when you cross the starting line, so that you begin the course with as much momentum as possible. Similarly at the finish, you don’t want to slow down until you’ve crossed the line and are off the course.
But you don’t want to be faster off the mark than the course permits. On many courses, the person setting the course will set up the first obstacle in such a way that the real hotshoes will find themselves in trouble as soon as they’re across the starting line.
When you walk the course, and as you sit at the start line waiting for your signal to begin, have a plan of attack on how you should negotiate the corner into the start line, based upon the direction you need to be going for the next two or three corners.
Similarly, there may be a complicated set of turns going into the finish that can trip up the unwary, causing them to be off the throttle just when they need a fast finish. Keep these possibilities in mind as you walk the course, and plan your strategies accordingly.
Gearing isn’t quite as complicated. With the MINI, your best bet on most courses is to start off in first, and then shift up into second as soon as you can. For the rest of the course, you can then just stay in second, confident that you’re well up in the rev range where you’ve got good torque for maneuvering. Few courses offer enough space to build up sufficient speed to justify a shift up into third or to require a downshift into first, and in most cases, the time you might gain by being in a better rev band will be lost by the time it takes to make the shift.

Setting Up the Car

During your first season, you don’t need to make many changes to the car. Most of your improvements in time will come through improvements in your own driving skill. In fact, the SCCA stock class places significant limits on what you can do to the car. In these classes you can make only a few changes to the engine. You can substitute a more efficient air filter, and replace the exhaust system behind the catalytic converter, but that’s about it on the power side.
On the suspension, you can substitute adjustable shocks and a front sway bar to reduce the car’s tendency to understeer. However, with the MINI’s excellent stock handling capabilities, it may take a season of practice before you would notice the difference in your time by these modifications.
What you can do within the limitations of the stock class is to replace the wheels and tires, so long as you stay within the stock sizes. Here you can make a great deal of difference in your lap times. As we’ve discussed above, by replace the stock wheels with a lighter-weight set you give the engine less mass to move. By mounting some good-performing tires to replace the run-flat tires that came with the car, you can get much better traction, and reduce the unsprung weight to boot.
If you get serious about autocrossing, you might consider buying tires that are designed specifically for racing, with a softer compound. However, these tires won’t last long at all if they’re also used on the street, so you would have to mount them on a separate set of wheels and put them on the car after you arrive at the event. Making this investment can certainly wait until you’ve worn out your first set of street tires and have gained the skill to take advantage of the improved tires.
But even if you decide to use the original run-flats for your first few events, experienced MINI autocrossers suggest that you can accomplish a lot by adjusting your tire pressures. You’ll probably want to increase the pressure on the tires so that they are less likely to roll. Inflate the fronts with about four pounds less pressure than the rear and you’ll do a lot to reduce the MINI’s basic understeering tendencies.
Another tip to find the right pressures is to make a mark with chalk or white shoe polish on the tire at the point where the tread joins the sidewall. If the mark is worn off after a run, then the tire is rolling over too far and you should increase the pressure that you’re running. Experiment with different pressures over the course of several sessions until you find a level that works best for you.
Be sure to check that the lug nuts are tight while you’re adjusting tire pressure and before going out on the track before every run. To be absolutely sure that they’re tight, you’ll need a “torque wrench” which measures the pound-feet of pressure required to twist the lug nut. You don’t need the best quality, since you won’t be using it every day, but a good one can be purchased for about $50. Tighten the lug nuts individually to 80 pound-feet and you’ll be sure that you won’t be singing, “You picked a fine time to leave me, loose wheel.”

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