At the Tour de France, bikes cannot weigh less than 6.8kg, a minimum limit set by the sport's governing body, the UCI, which applies in any race under its jurisdiction.
With some of the best teams in the world struggling to ensure they're not under the limit, you might expect every bike to achieve a weight as low as 6.8kg. But that'd be far from true, despite the amount of money and engineering expertise at teams' disposal and the supposed advantage that lower weight brings.
