Purely Custom’s Size Cycle is the ultimate fit bike for all types of bikefitting. On a fit bike there are no limits to findingthe biomechanically optimal seating position. The necessary adjustments can be done on the fly, i.e. while the cyclist remains on the bike. Purely Custom has developed and engineered the Size Cycle in a perfect way, with the input of the renowned Serotta International Cycling Institute (SICI). Two versions of the Size Cycle are available and the Pro version discussed here includes a computertrainer allowing for watt-based fittings.t.