Tour de France 2023: TOUR Tech briefing for Stage 18

Robert Kühnen

· 20.07.2023

Tour de France 2023: TOUR Tech briefing for Stage 18

Photo: Getty Velo

From July 1 to 23, the world's best cyclists will compete in the Tour de France. Victory and defeat on the roads of France will be decided not only by the legs, but also by the material. The TOUR Tech briefing for the 18th stage.

Add bookmark

Tour de France 2023 - Stage 18: Moutiers - Bourg-en-Bresse | 184.9 Kilometres

Photo: A.S.O.

The high mountains are done for now and on the 18th stage of the Tour de France 2023, the organisers have a heart for the heavy guys in the field: The route is largely flat, on 185 km only 1300 metres of altitude.

Potentially, there is therefore a sprint today. The field of sprint specialists is already somewhat thinned out. But that opens up more space for the men, who have so far just missed out on a top finish. The favourite, however, is once again the fastest man so far in the 2023 Tour de France, Jasper Philipsen.

Aero bikes are set for the final, anything else makes no sense at top speed. After all, at 65 km/h, around 90% of the resistance is due to air resistance. Today's final also climbs a few metres in the last 100 metres, which slows down the top speed somewhat at the end and requires adapted timing so that the power doesn't run out shortly before the finish line.

Sprinters experience three times more air resistance

One point we haven't looked at in detail so far is clothing. Aero one-piece suits are now standard on a flat stage. That's because the riders themselves cause most of the drag. Clothing can be used to influence the rider's aerodynamics - significantly. Compared to a good jersey and shorts combination, a perfectly matched one-piece can save power on the order of 50-100 watts at 65 km/h. As speed increases, the resistance to overcome air resistance increases massively (to the third power of speed): At 65 km/h, the power required to overcome air resistance is three times greater than at 45 km/h! A 20-watt difference at speed 45 thus becomes a 60-watt difference at sprint speed. Even the smallest details can therefore have a big effect in total. Mark Cavendish, who unfortunately crashed out of the race, was the first road sprinter to consistently apply the aero strategy of time trialists to sprinting.

Most read articles

When designing the suits, different strategies are used: A perfect wrinkle-free fit is the first step. The suits of the top riders are therefore tailor-made (starting in a classification jersey can be disadvantageous, because the team suit is better tuned in case of doubt). The second measure is even more sophisticated: the surface of the suit can be adjusted to the targeted race speed. This is done via the surface roughness. With the right amount of roughness in the right place (the thick thighs call for a much finer structure than the thin upper arms of professional cyclists; the upper arm fabrics often have recognisable fine-rib patterns), a turbulent boundary layer can be created in a targeted manner - these are air turbulences that supply fresh energy to the flow near the surface from the flow farther away from the body, which ultimately results in the flow being able to follow the contour of the body a little longer.

How do you like this article?

Tour de France 2023: Golf ball effect also effective in sprinting

If the flow is longer on the body due to cleverly placed fabric, the pressure differences in front of and behind the body are smaller; the rider feels this as less air resistance. The effect is also known as the golf ball effect; the dents in the ball make it fly further. The challenge with aero suits is placing the right fabric in the right place to maximise the effect for the relatively bulky human body.

Clothing is also fundamentally faster than bare skin, which is why long-sleeved suits dominate in time trials. Pants length has also increased. In Jumbo-Vismas team clothing, the knees just peek out. Long aero socks cover the lower half of the leg.
Unlike the bikes, we have no data on the specific suits used in the Tour de France and the riders in the suits. However, we know from our own tests in the wind tunnel that there is a lot to be gained on the field.

Number of the day: 14 hundredths of a second

Who has the fastest bike today for the expected sprint final on stage 18 of the Tour de France 2023? The usual suspects. The presumed fastest man, Jasper Philipsen, has the fastest bike in the 200-metre sprint. The Canyon Aeroad is 14 hundredths of a second ahead of a weak sprinter's bike, like the Bianchi Specialissima. Wout van Aert's Cervelo S5 is just as fast as the Canyon, with other models following at a close distance.

The (almost) complete field in the sprint over 200 metres

Photo: Robert Kühnen

*) The calculations are based on the bikes tested by TOUR in the laboratory and wind tunnel. The bikes at the Tour de France may differ in details. Of course, we have not yet been able to examine last-minute prototypes either.

Our Expert