I find that most mountain bike guide books do a pretty good job of describing trails and appropriate skills levels. That said, muni is a skill set unto itself, so when I think of muni as a skilled rider, a beginner mtb trail is a beginer muni trail, though it might be more challenging to someone who is a good road rider and not familiar with muni.
I adapted the following from the AWA kayaking:
- use -, + to differentiate within the grade
Class 1: Smooth surfaces, requires no maneuvering. (Skill Level: None). Ex: paved greenway.
Class 2: Some rough surfaces, small roots and rocks, requires minor obstacle avoidance (Skill Level: Basic). Ex: beginner mountain bike trails.
Class 3: Moderately rough surfaces, medium sized roots and rocks, requires considerable obstacle avoidance, moderate hill climbing and descending, small drops (< 30 cm), brakes and protective gear suggested. (Skill Level: intermediate). Ex: intermediate mountain bike trails.
Class 4: Very rough surfaces, large roots and rocks, considerable drops, sharp maneuvers may be needed, terrain exposure leads to increased risk of injury with falls, long and/or steep climbs, steep and technical downhills, protective gear and brakes highly recommended (Skill Level: advanced). Ex: advanced mountain bike trails.
Class 5: Extremes in surfaces variablity, very large roots and rocks, high risk of injury from falls, requires constant and aggressive obstacle avoidance, full protective gear and brakes required (Skill Level: Expert). Ex: Advanced Downhill bike trails.
Class 6: The gnar, huge rocks, huge drops, Class 6 is considered hazardous even for experts using state-of-the-art equipment, and come with the warning “danger to life or limb.” (Skill Level: Certifiable crazy). Ex: Riding down Everest.
