Published: October 18, 2012; updated: November 18, 2012
Today we will look at the different lines that can be driven on a race track, starting from why there is more than one line and ending with how you can find these lines yourself.
This is what is frequently called "the line", with the quotes sometimes explicitly rendered and sometimes implied.
School line is the line taught in lower levels in HPDE. It is frequently the only line taught in classrooms. It tends to be the line taught by in-car instructor for cars with "reasonable" power to grip ratio.
Generally speaking, the school line uses either a slightly late apex to guarantee that the driver never executes an early apex. In most corners, the driver is expected to brake in a straight line, most commonly on the outside of track parallel to track surface, but if that is not possible due to track geometry in as much of a straight line as possible as parallel to the outside edge of track as possible. Turn in point is usually all the way on the outside; the car then draws a slightly increasing radius arc through the apex and back to the outside as it is tracking out. The driver is expected to start getting on power shortly after the car passes the apex and should be at full throttle by the time the car is tracked out. Apex may be shifted a little more downtrack for novice drivers to reduce corner entry speed and stop the car from running out of pavement when it is tracking out under power.
The school line is, generally, the safest line through a corner, because it tends to have the lowest entry speed compared to the other lines. As a result, if a driver goes off course there is the least danger of damaging the car.
The school line is pretty fast. It is faster than naive lines taken by drivers unfamiliar with road course lines. However, because it prioritizes safety above lap time there are many corners where the school line is suboptimal. The faster lines aim to increase corner exit speed, mid corner speed or distance traveled through the corner, usually at the expense of reducing the amount of runoff or other safety margins available to the driver.
The school line is the base starting point for all other lines, and is the base from which drivers start when they are "finding the line" by themselves, that is without being told what the line is.
School line is determined almost entirely by geometry of the corner. Cars which exhibit strong understeer or oversteer or have too much power for the tires they run often have difficulties running the school line.
Qualifying line looks similar to the school line, but conceptually it is quite a different animal.
Qualifying line may be defined as "the line which produces the best lap time for a particular car, provided said car is alone on the course".
Usually qualifying line is discussed in the context of competition. As such the drivers tend to be more aggressive, and are prepared to endanger their car more than HPDE drivers. For example, in HPDE you would be encouraged to stay off curbs to have a safety margin in case you overdrive the car. In competition, you may want to use the entire curb in a particular corner, knowing that you have no runoff area left in that corner and therefore expecting to put two wheels off there at some point (frequently, "at some point" means at least once during each race weekend).
The ideal qualifying line would assume a perfect driver and would yield the absolute best possible lap time for the given car, leaving zero margin for error. The lines that drivers actually run in qualifying are those that produce the lowest lap times within the risks that each driver is prepared to take.
At the speeds and driving abilities involved in competition, qualifying lines are vehicle specific. The differences between FWD and RWD platforms as well as actual speeds and grip levels matter. Qualifying line avoids weak areas of the particular car being driven while maximing said car's strong areas.
Time Trial/Time Attack Line
This is conceptually exactly the same as the qualifying line, as time trials/time attack assume that each car is running by itself without interference from other cars.
In practice, time trial lines are somewhat more conservative than race qualifying lines because time trialers have a lower tolerance for damaging their cars as a result of driver errors.
Unlike qualifying and time trials, in racing each driver is normally battling multiple cars throughout the race. Race line is therefore the line that gives a particular car the best finishing position, given other cars participating in the race along with surface conditions and other factors shared with the qualifying line.
Race line is a compromise between defending one's position on track from cars behind and getting around the cars in front while maintaining pace compared to the field overall. Depending on whether there are cars behind and in front, race line may be entirely defensive or entirely offensive or it may be close to the qualifying line.
As is the case for the qualifying line, race line is car specific.
There is now a separate essay for the rain line.
Learning The Lines
The school line will generally be what your in-car instructor teaches you.
You may or may not learn the qualifying line in HPDE; this depends on the instructor and hosting organization policy. Some instructors, having progressed through HPDE ladder but never competed, tend not to push hard enough for the differences between the school line and the qualifying line to matter. Some of these instructors may be entirely unaware of what the qualifying line might be, having never driven it. Similarly there are orginizations subscribing to the viewpoint that anyone driving over 8/10ths should not be participating in their track events, and will be less than helpful in getting you over 8/10ths.
There are principles that you can use to help you learn the qualifying line. Ultimately, the qualifying line is validated by lap times.
What are some of these principles for a qualifying line?
You want to maximize straightaway speed and the time spent on throttle. This affects both corner exit and corner entry - corner exit is obvious but corner entry is also important: if you can keep straightaway speed for longer and enter a corner which is slow anyway later, you could gain an advantage in lap time.
Maximizing time spent on throttle may also result in unconventional lines through corners, for example creating a straight between two corners that can be taken as two connected arcs if this allows you to be on full throttle over the straightaway.
Generally speaking, you want to corner at the maximum possible cornering (mid-corner) speed that does not compromise your exit speed. Technically the same goal can be applied to the school line, but practically speaking once a driver executes the school line at roughly 8/10ths they are not encouraged to go faster in HPDE, whereas in competition running at 8/10ths is more of a beginning of the performance envelope.
Finding the rain line requires knowing the principles behind it and even more experimentation, plus it cannot really be found in dry conditions (but you can ask experienced racers what it is, and practice your understanding of it even when it is dry).
Learning The Race Line
Driving a race line is easier than you might think. Pick a side to stay on - either left or right. Then go around the track, leaving about a car width on your right or left respectively for the imaginary car you are racing.
Essentially you have now changed the geometry of the track. While your turn-in and braking points will be close to the school line, they won't be the same. This gives you two additional lines you can figure out, work on and practice at any track you go to.
If you have a lap timer, see how close you can get to the qualifying time while staying on either half of the track.
Another interesting exercise is determining if one side of the track is faster than the other side. This is the age-old distance vs speed argument.
Here is how you can put everything together. Start on the left side of the track. Do two laps to set a base time on the left. Now switch to the right and run laps on the right until you beat your left time, but no fewer than two laps on the right. Switch to the left side and run until you beat your right time, but no fewer than two laps. And so on. You might find that alternating sides like this helps you improve your lap times on both sides - most likely this is due to you sensing traction better which translates to carrying more speed everywhere on the track.
Note: leaving one car width is not the same as using half of track width as is normally expected in open passing HPDE events. Leave one car width when you are by yourself, but leave half of track width when you are passing or being passed.