Tour de France Femmes Tech Briefing: The fastest set-up for the individual time trial

The fourth stage is a 21-kilometre time trial from Gevrey-Chambertin to Dijon. Last year’s Tour de France Femmes did not feature a time trial, but this year this stage is likely to play a key role in determining the overall result. Although the route is short, time gaps of between one and two minutes are still possible, even among very strong riders.

Time trial specialist Marlen Reusser is expected to battle it out with Demi Vollering for the stage win here. The pure climbers will be at a disadvantage and are likely to fall well behind.

The riders must tackle a 1.8-kilometre climb with a gradient of 6.9 per cent; at the highest point, they will circle the village of Corcelles-Les-Monts before beginning the descent towards Dijon. The downhill section is a straight, high-speed descent. It is not until two kilometres before the finish that the first of four sharp bends slows the riders down.

The female riders will reach enormous speeds on the descents whilst maintaining an aerodynamic position, much as we have seen with the men.

It will be interesting to see how the female riders set up their gear systems. Will they opt for ‘monster’ single chainrings, like the men, to be able to pedal effectively at high speeds? Presumably, the riders will tend to opt for double-chainring set-ups and accept the limit on chainring size dictated by the front derailleur.

​The equation of the day: five watts = twelve seconds

To investigate the effect of materials on the track, we are simulating ten different, fictitious set-ups – TT1 to TT10 – with varying aerodynamic characteristics and weights.

Time trial bikes are the order of the day. Although the pace drops to around 23 km/h for a few minutes on the steepest section of the climb, we expect an average speed of around 47 km/h overall.

At these speeds, every little aerodynamic detail counts. Aerodynamic advantages more than make up for the losses caused by excess weight on the climb. According to our calculations, this corresponds to five Aero-Watt: around twelve seconds off the ride time. Five watts – that could be the right pair of aero socks, a detail on your suit or helmet, or a particularly fast wheelset with an aero front tyre.

By contrast, an extra kilo of weight costs only around five seconds. Optimisation therefore focuses first on aerodynamics, with weight coming second.

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

​The table shows that aerodynamics matter significantly more than weight – even though the time trial includes a 7 per cent gradient. The calculations are based on a rider weight of 57 kilos. A comparison of TT6 and TT1 shows that a five-watt aerodynamic saving (at 45 km/h) yields a net advantage of seven seconds over a bike weighing one kilo less (TT1). Nevertheless, weight does matter. An extra kilo of weight, with the same aerodynamic performance, equates to around five seconds’ additional riding time.

* 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 hill climbs and proper final sprints. Taken together, this makes the simulation very realistic. What we cannot replicate are dynamic handling 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.