The UCI has been spotted measuring rider socks ahead of the Tour de France 2019 team time trial.

Cycling’s governing body had a representative checking the height of aero socks and overshoes at the start of stage two, with a picture of a Sunweb rider being scrutinised emerging online.

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The UCI has been using a special device to measure the kit, but why are officials measuring socks at the Tour de France 2019 and what are the rules?

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At the start of the season, the organisation reintroduced sock height rules which state: “Socks and overshoes used in competition may not rise above the height defined by half the distance between the middle of the lateral malleolus and the middle of the fibula head.”

Get it?

Well, the UCI also released a handy illustration to ensure teams don’t find themselves breaking the rule.

In short, the sock must not breach the halfway mark between the ankle and the bottom of the knee.

The regulation did not specify how the rule will be enforced, or what the punishment would be, but we have now seen the measuring device used to check riders’ legs.

The sock rule is part of a UCI crackdown on clothing being used for aerodynamic gains, and came as regulations were extended to ban kit that changes the shape of a rider and forbids non-essential clothing or devices used for purposes other than for protection.

Rules for 2019 say changes to clothing surface are allowed, but only by assembling the fabric, by weaving or by threading.

Surface roughness of clothing must not exceed 1mm at most and items must not contain any self-supporting elements or rigid parts.

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The UCI had previously regulated sock height but that rule had disappeared from the books in recent years.

But the organisation has not set a minimum length, which means some riders will be allowed to a commit fashion crime of the worst order – wearing socks that are too short.