S0 - very easy:
The lightest Singetrail type is characterized by a slight to moderate gradient, non-slip surface and extensive curves. For his accomplishment, no special demands are made on the driving technique.
S1 - easy:
Here you can count on smaller obstacles such as roots or stones. Partially unconsolidated surface and the curves become narrower, but without hairpin bends. The maximum gradient is 40% here.
S2 - medium:
The difficulty grows and you can expect bigger stones and roots. Rarely solid ground under the wheels and there are flat steps or stairs. Tighter turns are also regular and the steepness can be up to 70%.
S3 - difficult:
In this category you move already in blocked terrain with larger boulders or longer root passages. Switchbacks and slanting occur and you often have to expect loose ground. Regular slopes of 70% are present.
S4 - very difficult:
It is steep and correctly blocked. Long, challenging root passages and large boulders must be overcome and loose boulders are the order of the day. Switchbacks and steep ramps place special demands on the driving technique and there are steps in which the chainring comes up.
S5 - extremely heavy:
The upper end of the scale is characterized by heavily blocked terrain, ridges, loose ground with boulders, tight switchbacks and high obstacles, such as fallen trees - of course including a steep incline. There is little braking distance and the MTB driving technique is put to the test.