In the racing track there is not the use of stop lights for many security reasons and technical regulations.
When we decide to change our rearsets and we want to buy the racing ones that are for racing track use we must remember that the stop sensor of the back brake is not working (with the exception of some motorbikes such as BMW S1000RR that have brakes system with oil pressure tracer that allows the stop light to work).
In case you may need to keep the back stop functioning, you can buy a switch (known as idrostop that is a oil pressure sensor for brake lights) to put inside the back brake pump; it has a oil pressure tracer and sends a signal for lightening of the stop light).
How much is the back brake relevant?
On a scale of 1 to10 someone can say 2, others 5 others nothing but for sure your passenger’s answer would be 10 to relieve his stress and troubles.
As far as our experience we can say that the back brake has to balance the vehicle trim in the bends adjusting the speed or the direction steadiness.
It is impossible to establish strict rules for its use as it depends from the rider experience on the road and on the race track.
Surely the most important brake is the front one that allows you to decelerate very quickly.
The back brake is not able to stop immediately the vehicle so even if the stop light is not working it would be very difficult to make a danger situation.