Glossary

Glossary of Autocross Terms
Apex: The middle of of a corner, where you want the car to come as close to the inside of the turn as possible. Depending on the turn, you may want the car to reach the innermost part of the corner after the actual middle (late apex). See diagram 1.

Camber: How far your wheels tilt in or out towards the top on a vertical axis. Generally, negative camber helps even the load across the tires during cornering. This can be demonstrated with a pyrometer (infrared thermometer). "More camber" refers to increasing negative camber, since positive camber is useless in autocrossing. See photo.

Course Deviation: Completely missing a gate or taking a wrong turn on the course. A course deviation, or "CD", will cost you twenty seconds. Two "CD"s will give you a DNF.

DNF: Short for "Did Not Finish". You will not get a score for a DNF. Either you had to get pushed/towed off the course, or you missed at least two gates.

Drift (slip angle): Partial loss of traction resulting in the car sliding slightly wide of where you point it. This can be the fastest way through a corner, provided that you maintain mostly forward momentum and only deviate from the direction your tires are pointed by about 6-12%. Slicks can maintain speed at a higher slip angle than street tires. Rule of thumb: if you are going more sideways than forward, or losing speed, you are drifting too much. If you aren't drifting at all, you are going too slow.

Gate: Two or more cones that you must drive between to stay on course. A series of gates makes up the layout of the course. Miss one, and you have a Course Deviation. Marker cones (cones sitting on their side) often point towards the gates to help you out.

Grid: Where the cars line up in rows waiting to make a run. The numbers on your windshield designate where you line up in the grid. There will always be at least one worker to help you get lined up.

Line: A mental line of travel you want the car to take to maximize speed through the turns, and ultimately the whole course. Try to pick a line that causes the least amount of turning the wheel, maximizes straightaways, and minimizes time the car is not traveling in a straight line. This is usually determined when walking the course before the event.

Marker: A cone or series of cones lying down. The cone they seem to be pointing at is the one you have to go around. There are several examples in the photo above. If you happen to hit a marker cone when you plow through a gate, it won't count against you. Only the actual gate cones count.

Overdriving, or overcooking: When you enter a turn too fast and the car's momentum continues forward after the point where you intended to enter the turn. Almost all novices will do this, and even experienced drivers often battle with entering a turn too fast. This causes slower times, premature wear on tires, cone murder, and comments like "My car understeers like crazy!" Slowing down sooner and letting off the brakes before turning in allows the chassis to balance and alleviate most of the problem.

Oversteer: When the back tires lose traction and carry momentum straight while the front of the car is turning. More common in RWD cars, and can be used to pivot a car around a turn. There are three common ways to cause oversteer. All are variations on unsettling the chassis: 1. Lots of throttle when weight is transferred to the front or side of the car; 2. Lift off the throttle in a fast turn (especially in a sweeper), causing the weight transfer to push the rear out; 3. Trail braking with too much exuberance. Tsuchiya-san would add that you can induce oversteer with the E-brake, the feint (twitching the wheel one way off throttle, then turning the other way on throttle), and dumping the clutch while downshifting, but those methods are more common in other motorsports. (though I admit to using the feint sometimes in my FWD car during autocross) The crazy uncle of oversteer is "snap-oversteer". This occurs when you brake hard, get a little sideways, turn the wheel opposite to correct, and the momentum of the rear causes the car to spin out. If you feel it happening, it is too late to do anything about it.

Paddock: Where uninvolved cars, trailers, and equipment are kept during an event. Only cars involved in the current heat are in grid. Everything else stays in the paddock.

PAX Index: Stands for "Professional AutoX", perhaps better explained as RTP, meaning "Racer's Theoretical Performance". So you still don't know what it is... It is a handicapping system that applies a multiplier to your time to compare it evenly with other cars in different classes. That way the driver of a Geo Metro can be evenly judged against the driver of a Lotus Elise, more or less. There's still no accounting for taste.

Pivot: A sharp turn (over 90%) or hairpin, usually designated by one or three large cones. Mad skills are required to negotiate pivots successfully.

R Compound Tires: These tires have treadwear ratings of under 140, and wear out quickly. Most have little or no tread pattern, and are not suitable for daily driving. They are legal in all classes except Street Tire, STS, STX, and STU. R compound tires provide much more grip than street tires, and can improve run times by 2-3 seconds. Some come in soft and hard compound variations depending on your needs. Popular versions are available from Kumho, Hoosier, Yokohama, Avon, and Goodyear.

Reference Point: Cones or landmarks chosen when walking the course that you use to judge where to brake or aim the car. Since things go by so quickly on the course, it is helpful to decide ahead of time what reference points you will use.

Red Flag: A red flag on the couse tells the driver to come to a complete stop, because something has gone wrong. It may be an obstacle on the course, or some other problem that requires you to stop. If you are red flagged because of something you did not cause, you will get a rerun if you come to a stop.
Slalom: A series of cones laid out in a line that require you to zig zag around them. often, the decision is yours whether to start on the left or right of the first cone.

Spotter: The course worker(s) who stays close to the timer and watches the cars on the course, alerting the timer of downed cones, red flags, and when the next car needs to wait to start if there is a problem.

Street Tires: Tires having a treadwear of over 140 and section width of 225mm or less. Suitable for Street Tire classes STS, STX, and STU. Most street tires best-designed for autocross have a treadwear of around 200. Examples are Kumho MX and Falken Azenis RT series. Typical summer performance tires have a treadwear of over 300, and all-season radials are likely to run between 450-600. Popular "High Performance Tires" are designed for wet and dry traction, and last long enough to warranty. Any street tires can be used to autocross, but as a rule of thumb, wide, low profile tires with large outer tread blocks and a low treadwear rating are optimal.

Trail Braking: A tricky technique of still having your foot gently on the brake while entering a turn. The idea is to keep the weight of the car transferred more to the front, allowing the back of the car to rotate. See "Oversteer".

Treadwear Rating: See Street Tires and R Compound Tires. There is no set measurement across tire brands for determining how long the tread is expected to last. Touring tires are designed to last 30-60 thousand miles, and are made of hard rubber compounds. Their treadwear rating is very high, sometimes over 600. Their gripping capabilities may excel in mud and snow, but they are useless on the track. Sticky R compound tires may have a treadwear of 80, meaning they won't last long at all, but will grip like nobodies business. Most OEM tires on performance cars are in the neighborhood of 330-450 treadwear.

Understeer: The tendency of a car to go straight instead of turning when the tires are pushed to their grip limit. Also known as pushing. (See overdriving/overcooking). This is one of the most annoying handling characteristics of stock vehicles, especially front wheel drives. Cars are set up from the factory to understeer, because it is safer for the average person to deal with understeer than oversteer in an emergency braking situation on the street. The inherent characteristics of an FWD (front wheel drive) car; front engine, front drive, front wheels doing all the turning and most of the braking, make the front wheels do all the work. This causes them to run out of traction if they are trying to do too many things at once. This is best demonstrated if you try to brake hard and turn at the same time. The car goes straight ahead since it is too busy trying to stop to bother with your annoying pleas to "TURN TURN TURN!". Much of this can be addressed by training the driver. The rest can be handled with stiffer springs, larger stabilizer bars, and tire size/pressure adjustment, in respective order from drastic to subtle.

Wall: A line of cones placed to prevent you from missing a not-so-obvious change of direction on the course. Also evident on the photo at the top of the page.

This is by no means an all-inclusive list, leaving out items like the Chicago Box, decreasing radius turn, heel-toe shifting, corner weighting, etc. Some great books to help you learn more are: Secrets of Solo Racing by Henry A. Watts; and Speed Secrets (I-III) by Ross Bentley. The Solo II Rulebook is also downloadable from the SCCA website.