Tour de France 2023 - 18th stage: Moutiers - Bourg-en-Bresse | 184.9 kilometres
The big mountains are over for now and on the 18th stage of the Tour de France 2023, the organisers have a heart for the tough guys in the peloton: the route is largely flat, with only 1300 metres of elevation gain over 185 kilometres.
There is therefore potentially a sprint on stage 18. The field of sprint specialists is already somewhat thinned out. But that opens up more space for the men who have narrowly missed out on a top place so far. However, the favourite is once again the fastest man of the 2023 Tour de France so far, Jasper Philipsen.
Aero racing bikes are set for the final, everything else makes no sense at top speed. After all, at 65 km/h, around 90 per cent of the resistance is due to air resistance. The final also climbs a few metres in the last 100 metres, which slows down the top speed a little towards the end and requires adapted timing so that you don't run out of power just before the finish line.
Sprinters experience three times more air resistance
One point that we haven't looked at in detail so far is clothing. Aero one-piece suits are now standard on a flat stage. This is because the riders themselves cause most of the aerodynamic drag. The rider's aerodynamics can be significantly influenced by the clothing. Compared to a good jersey and shorts combination, a perfectly tuned one-piece can save around 50-100 watts of power at 65 kilometres per hour. The resistance to overcome air resistance increases massively with speed (to the third power of speed): At 65 km/h, the power required to overcome air resistance is three times as high as at 45 km/h! A 20-watt difference at 45 km/h thus becomes a 60-watt difference at sprint speed.
Even the smallest of details can have a big impact. Mark Cavendish, who unfortunately dropped out due to his crash, was the first road sprinter to consistently transfer the aero strategy of the time trialists to sprinting.
Various strategies are used when designing the suits: a perfect, crease-free fit is the first step. The suits of the top riders are therefore customised (starting in a classification jersey can be disadvantageous because the team suit is better adjusted 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 require a much finer structure than the thin upper arms of professional cyclists; the upper arm fabrics often have a recognisable fine rib pattern), a turbulent boundary layer can be created in a targeted manner - these are air turbulences that add fresh energy to the flow close to the surface from the flow further away from the body, which ultimately means that the flow can follow the contour of the body for a little longer.
Golf ball effect also effective in sprint at Tour de France 2023
If the airflow is in contact with the body for longer due to skilfully placed fabric, the pressure differences in front of and behind the body are smaller, which the rider feels 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 time trial suits is to place 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. The length of trousers has also increased. With jumbo visors, the knees just peek out. Long aero socks cover the lower half of the leg.
Unlike the racing bikes, we have no data on the actual suits used in the Tour de France or the riders wearing them. 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 racing bike for the expected sprint final? 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 close behind.
The (almost) complete field in the 200 metre sprint
*) 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 some details. Of course, we have not yet been able to analyse last-minute prototypes. Background to the simulation.
Our expert
Robert Kühnen studied mechanical engineering, writes about technical and training topics for TOUR and develops test methods. Robert has been refining the simulation calculations for years and they are also used by professional teams.
