Bicycle construction is limited by regulations covering dimensions and other features such as weight. UCI Regulations At the professional level, time trials (TTs) are frequently accompanied by motorcycles, some carrying video equipment or race officials, and riders may be followed by a team car carrying coaches and spare parts, but the cyclists are not permitted to draft behind the vehicles. Race regulations typically dictate a minimum distance behind the cyclist which the car must maintain and a minimum gap that must exist between two cyclists before the car may enter that gap.