TOUR Tech Briefing for Stage 12: Sprint simulation and data from a solo breakaway

​From 4 July to 26 July, the world’s best cyclists will be competing in the Tour de France. Victory and defeat on the roads of France will be decided not only by the riders’ legs, but also by their equipment. The TOUR Tech Briefing for Stage 12.

The twelfth stage is the last true flat sprint stage of the Tour. Stage 17 may still offer opportunities for sprinters. The final stage in Paris, featuring three ascents of Montmartre Hill – as tested last year – is no longer purely a sprinter’s stage.

Sprinters have had better times at the Tour de France. In the past, more stages followed this pattern: breakaway riders made their move, the peloton controlled the race, and there was a sprint finish. For their race within the race, the sprinters accepted having to ride over countless mountains. But even the mountain stages were organised. In the gruppetto, the heavier riders would help one another to stay within the time limit. Today, the stages are shorter, the pace much higher, and the organisers are doing their utmost to ensure that there are no more boring transition stages where riders simply cover the distance, only to face a sprint at the end.

Less boredom is good for the spectators, but it increases the pressure on the remaining sprinters to perform on those rarer occasions. Or to adapt and ride more in the style of a classics specialist.

This should make the sprinters’ teams all the more determined to ensure that today’s race ends in a sprint finish.

The final stretch features its last bottleneck – a sharp left-hand bend – 2,300 metres from the finish line. From there on, the route runs along the River Saône, offering a clear view. It is not the sort of terrain where a surprise attack could be launched just before the finish.

Stage twelve: The script calls for a sprint. Will the sprinters’ teams give it their all?

We’ve already simulated several sprints. What else could we try that might yield new insights? We’ll shorten the sprint and simulate accelerating out of a slipstream: a sprint starting at a higher initial speed – 65 km/h – launched 150 metres before the finish line.

Under these conditions, which bike has the tyre at the front?

Number of the day: two thousandths of a second

​The most aerodynamic bike in the field clinched victory by two thousandths: first place for van Rysel, second for Cervelo – the usual suspects.

Decathlon’s sprinter, Olav Kooij, is therefore in an excellent position as far as equipment is concerned. The bike’s slight excess weight does not hinder his final acceleration.

​Final 150-metre sprint: The sprinter, who emerges from the slipstream late but still has plenty of energy left, accelerates the bike to 71 km/h as he crosses the finish line. The final sprint is short, lasting just eight seconds, but positioning oneself beforehand also takes its toll.

An overview of the (almost) full line-up*:

​The table shows that, once again, the bike with the best aerodynamics comes out on top in the short, explosive final sprint over 150 metres.

The “Aero-Power” figure shown is the power measured by TOUR in the wind tunnel to overcome the aerodynamic drag of the bike and a dummy with moving legs at 45 km/h. For the simulation, we mathematically add the rider’s upper body and scale the drag to the actual race speed.

Performance data from a solo breakaway

A handful of professionals post real power data from the Tour on Strava. One of them is Baptiste Veistroffer, Team Lotto Intermarché’s breakaway king at this year’s Tour.

His performance in the fifth stage, during which he led a long solo breakaway until 14 kilometres from the finish, shows what it takes to break away from the peloton and keep the pack at bay for so long.

His breakaway begins with a sprint just a few kilometres after the start. He reaches a maximum power output of 1358 W and maintains an average of 1114 W over 12 seconds. Veistroffer accelerates to 67 km/h on a slight downhill section and then continues at a power output of around 330 W.

He maintains this power output very consistently. His average power for the entire stage was 323 W. His normalised power, which places greater weight on the peaks, was 343 W – only slightly higher than his average power – meaning that his effort was very consistent, which is typical of a long solo breakaway. His average speed over the entire stage, which he covered largely on his own, was an impressive 44.1 km/h.

His flight is characterised by steady, sustained power and an efficient aerodynamic posture maintained over long periods.

​* Simulation calculations

Based on our own wind tunnel tests, we carry out simulation calculations for the Tour de France tech briefing. How TOUR tests: Aero road bike test in the wind tunnel.

We are investigating which wheels can offer a technical advantage in which situations. The variables we can control in the simulation include wheel weight, rider weight, the inertia of the wheels, the drag coefficient, the rolling resistance coefficient and the efficiency of the drivetrain.

To model ride times, we use realistic power outputs and weights for the riders, combine these with our wind tunnel data, and have the riders race virtually along selected sections of the route, which we extract from the official route data; the derived elevation profiles are key to this. The modelling also includes bends, which we can brake for realistically, and adjustable power profiles for different types of riders. This allows us to distinguish between attacks on climbs and proper final sprints. Taken together, this makes the simulation very realistic. What we cannot replicate, however, are dynamic riding effects such as the individual behaviour of the wheels on different surfaces.

The journey times calculated for the sections of the route that are decisive for the race highlight the influence of the wheels – provided that the riders always behave in the same way in a given scenario.