Mountain bikes feature strong frames and components, off road tyres and a large range of gears. They are primarily for off road use, but also extremely versatile, and suitable for a variety of recreational and commuter purposes. Entry level MTBs are more suited to bike paths, parks, and some light use on unsealed surfaces. Progressing through the range, bikes become more suited to longer rides, and rougher terrain, with a focus on durability and performance. MTBs can be either hard tail (front suspension only); or dual suspension (suspension in front and rear). Within each of these categories, there are also a number of wheel sizes (26”, 27.5” and 29”) that each provides their own advantages. Carbon frames achieve a big advance in performance, as the material is extremely strong, light, and stiff, achieving maximum power transfer from rider to bike.