8 cm and the minimum thickness 2.5 cm. The minimum thickness shall be reduced to 1 cm for the chain stays and the seat stays. The minimum thickness of the elements of the front fork shall be 1 cm; these may be straight or curved. The top tube may slope, provided that this element fits within a horizontal template defined by a maximum height of 16 cm and a minimum thickness of 2.5 cm Note that the regulations regarding the dimensions of the bike are allowed exception, given that the rider can demonstrate a morphological need for the exception based on limb size or other factors. These rules effectively and purposely rule out recumbent bicycles, and have done so since 1934. See also Bicycle Bicycle frame Bicycle racing Outline of cycling Road cycling References External links Road bicycle racing terminology Cycle types Racing vehicles Road cycles