The rebuildable rear nitrogen shock absorbers of YSS's Top Line series can be used on scooters only. They are notable for their high performance when riding in the difficult, "uneven" conditions of urban routes, since the options for adjusting their spring and their rebound damping — combined with the internal nitrogen bottle — work together perfectly and give the rider comfort and immediate feedback. The spring preload is adjusted through a fine thread and using the special adjusting tool, which is included in their pack. By screwing the shock absorber, the user can "turn" the spring preload so as to find the ideal setting. The rebound damping can be set by hand to "fast" or "slow", with the return time adjusted from a special selector on the internal nitrogen bottle. Available now for the SYM Maxsym 400 11-15.