Providing a well-maintained cycling infrastructure has a positive impact on the comfort and safety of cycling in road traffic and creates the conditions for its acceptance as an alternative to private or public transport. This study uses data from smartphone accelerometers and a k-means++ algorithm to determine the quality of road sections. This is easy and cost-effective to apply to large-scale cycling networks and shows in a case study for the city of Salzburg that poorly passable lane sections can be well localised and subsequently maintained in a targeted manner.