Why are curbs used in motorsport?
Curbs are used primarily as boundaries in motorsports.
There are several different types of curbs depending the circuit as well as the highest paying series that is going to leverage the circuit as a venue for one of it's events.
The FIA or Fédération Internationale de l'Automobile is governance body that most international motorsports adheres to. A race series will often look to the FIA as a sanctioning body for fees.
Part of the FIA's responsibilities to the series include circuit adherence to specific rules that define safety for drivers, cars, racing circuits and emergency response personal.
Circuits are graded by the FIA. The grading is associated with particular types of racing. A lower grade may have safety standards that comply with the needs of a GT car. Licenses Grade 1 applies to Formula 1 racing which requires higher safety standards due to the extreme speeds.
Kerbs are primarily considered a component of circuit safety. Kerbs have many different designs. Some are known for their height and others for their width as well as placement. Many are designed to slow a driver down. Exit kerbs will frequently have a washboard design reduce adhesion should a driver place a wheel on the surface. This helps to ensure drivers will stay within a boundary that is designated.
The kerb will serve as a buffer between the track surface and the adjoining surroundings. Drivers exceeding the boundaries can damage their vehicles on some kerbing.
Kerbing design of particular corners can define that corner for decades creating awe at how drivers of the years approach the corner and deal with kerbing. Some corners known to destroy components and others are known for their smooth transition allowing drivers to use the area to their benefit.
Particular kerbs at certain circuits have controversy surrounding them. This is not uncommon. In this case former Ferrari driver Felipe Massa destroyed part of his right front suspension hitting a kerb which resulted in a crash during his qualifying for the race.
A quote from this article states
The barriers have also been moved back over the past two decades to give drivers more breathing room if they get the corner wrong.
However, organisers have recently installed a bunch of speed humps in the run-off area on the inside of the Raidillon curve to deter drivers from constantly trying to straighten out the corner too much.
This is the result of the change to the kerbing. Needless to say this was changed before the next race.