According to UCI regulations, placing objects on the chest is prohibited. Article 1.3.033 stipulates that clothing must serve only the function of clothing and must not artificially alter the body shape of the rider.
“This is clearly not okay,” Bert Blocken, professor of aerodynamics at Heriot-Watt University in Scotland and LUT in Finland, said.
The finish of stage 2 of the Tour de France Femmes
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Referred to as 'chest fairing', increasing the surface area of the chest can change the airflow around the cyclist during the time trial and thus create a measurable benefit over the course of multiple kilometers.
“We are talking about a Chest Fairing, which alters the airflow around the body, thereby reducing overpressure on the thighs. As a result, the rider experiences less air resistance. It is not that you gain a benefit of tens of seconds with this in a time trial, but in a ride of 20 to 30 kilometers, it can yield seconds that can be decisive."
Blocken completed extensive research into chest fairings for time trialists and triathletes, which was published on ScienceDirect on two years ago. It concluded that you can achieve a reduction in air resistance of up to 3.6% when using an object in the most optimal shape that covers the chest. This translates into a time saving of at least 0.78 seconds per kilometer.
“I spoke about it with Michael Rogers of the International Cycling Union (UCI) at the time. Back then, it was mainly about the 'abuse' of radio communication, which was placed on the front of the chest to reduce air resistance. I pointed out our research to him. So the UCI is aware that this is an issue.”
UCI guidelines
As per UCI guidelines, attaching items to or under the chest to create a more streamlined shape is not permitted. Texture differences to enhance aerodynamics are only permitted if they are woven or stitched directly into the fabric (with a maximum surface height difference of 1 mm).
If a rider is caught violating the rule during or after a race, immediate disqualification from the competition will follow.
Depending on the level of the competition, a fine will also be imposed, usually ranging from CHF 200 to CHF 1,000.