Hairpins are tight turns, normally one 180's on the track.  They can be challenging since there is no right way around the hairpin.  For example the way we normally go around a turn is out, apex, out.  We have long turn, with an average speed of 44mph.

A much faster away around the track is to come in fast and break hard at the first apex and use all your traction to turn from point a to turn b, and then power out of the hairpin, this leads to an exit speed of 77mph in this example.  If there was a long straight this would be very important, as we know from physics that the final velocity of an object is v initial plus the acceleration multiplied by the time.  That initial velocity is what will win a race with when two cars have equal max acceleration.

Race tracks are much more complex then just rights and hairpins, to add to this complexity is the fact that a race car is a dynamic system.  Your suspension might deflect, and if you are truly on the line, you don't have an out.  (Chassis Engineering)  For example if you apex early on the second apex you going to drive off the track.  One mistake and your done for the race.  Another bad case is if your feeling good and come in to fast, since the resulting vector will have a grater magnitude then your tires can take you will slide off at a tangent of your turn, so you will end up off the track between points a and b.  Because of this, many racing teams use a program called rars.  (Physics of Racing)  It has many popular tracks, and different styles of racing, and cars.  It shows how the cars take the tracks, and has little lines for the apex.  This can help the driver find the line.