Off-Road Mountain Biking: A profile of participants, setting and preferences, by Gordan Cessford, 1995

Talks about the four main impact damage from mtn biking and the affects of their use.

1.2.1 Physical Impacts of Mountain Biking

Like the physical impacts of foot traffic, those of mountain biking are concentrated on tracks. The four main impact damage problems arising from recreation use of tracks are:

- excessive erosion from enhanced water flows and disturbed soil surfaces on sloping sections of track, and at natural or managed drainage points across them.

- muddy stretches in water-saturated sections of tracks, often including major disruption of soil structure, and lateral spread of tracks.

- development of lateral spread and multiple parallel tracks, where the track surface is harder to travel on than the adjacent surfaces (e.g., too rocky, muddy, deeply incised, slippery).

- development of informal tracks, including shortcuts on corners and switchbacks, and around focal points such as huts, campsites, attractions, and viewpoints.

Although comparative research is not extensive, it appears that the `foot-action' effects of walkers may in some cases more disruptive to track surfaces (particularly on downhill sections), than are the `wheel-action' effects of mountain bikes. The distinctly unique impact effect of mountain bikes is the linear tyre-track produced, particularly in soft or wet surfaces. When this effect is accompanied by downhill skidding through over-braking, it can contribute to development of `ruts', which over time may form erosive channels for water on sloping sections of track. 

However, despite the different types of effects from mountain bikes and walkers, research provides no conclusive evidence that one is any `worse' than the other in the overall degree of impact created. General impact research indicates that the location and condition of the track (particularly with regard to drainage); the number of users overall; and the individual behaviour of these users, are more important for the development of track impacts than are differences in the type of recreation activity (e.g., walking and mountain biking).