Mountain biking is a popular activity in both outdoor recreation and mountain tourism. Trail difficulty rating systems attempt to help visitors to match their own skill level with the technical difficulties of recreational trails. However, the perception of trail difficulty might be related to factors like age, gender, actual skill level or mountain biking experience. This study compares (1) the perceived trail difficulties between different groups and (2) differences between self-assessed skill-level and actually manageable maximum grade of difficulty. Participants (n = 2040) were asked in an online survey to assess the trail difficulty of 30 selected mountain bike trails. These trails were presented by pictures varying in technical difficulty according to the six grades of the Singletrail-Skala (STS; 5 pictures of each grade of difficulty). The STS is a difficulty rating system for mountain bike trails used by several destinations in the European alps as well as by some internet platforms that offer mountain bike gps-tracks or maps. Individuals’ actual maximum grade of difficulty according to STS was determined by asking whether participants would manage to ride a certain trail or not. Findings show that the perceived difficulty of a trail increases as the skill level of a participant decreases. No other factors affecting the perceived difficulty could be identified. Furthermore, participants’ self-assessed skill level differs from their actual maximum grade of difficulty according to STS. Whereas beginners underestimate their skill-level, more experienced mountain bikers overestimate their skill-level. Additionally, especially male mountain bike riders tend to overestimate their skill-level. In general, correlations between self-assessed riding skills and actual maximum grade of difficulty are low. The findings of this study provide information for the development and implementation of mountain bike trail difficulty ratings.