Velon data explainer: Speed
An individual time trial in the Ard├Ęche at the 2016 TdF (Icon Sport/Icon Sport via Getty)

We asked BMC Racing Team’s Rohan Dennis and Dr Dan Dywer, Senior Lecturer in Applied Sport Science at Deakin University in Geelong, Victoria, to help explain the principles of the four categories of Velon’s live race data: power, cadence, heart rate and in our first article, speed.


Data explainer: Speed

It seems simple when it comes to bike racing. The fastest rider wins, right? Not always.

In a Grand Tour the GC (General Classification) records overall time and therefore overall speed. The rider that completes the three-week race in the shortest time wins. But within that, all kinds of complications come into play.

A GC rider like Chris Froome (Team Sky) or Nairo Quintana (Movistar Team) will be nowhere near the fastest rider on the majority of stages – and will spend much of the race expending less effort than their team-mates. But their cumulative time including mountain climbs, time trials and flat stages combined can put them on the top step of the podium: it’s a test of their all round skills.

Cut through the jargon:

Time trials

Time trials are about speed, but not a short, sharp burst like sprints: it’s about who can travel from Point A to Point B in the shortest time, sustaining a similar intensity throughout.

Dr Dwyer explains: “In a time trial on a relatively flat course, cyclists are at an equilibrium point – the power at which they can sustain for say, 45-odd minutes, for the duration of a time trial, and the speed that coincides with that power output. So there’s this balance between the power they produce and the air resistance working against them to determine their speed.

“Power production is number one in the factors that determine speed. On the flat there is a ‘cubed’ relationship, meaning to the power of three, between power output and velocity. It’s not a straight relationship. If you double your power, you don’t double your velocity.

“You can also increase velocity by adopting a more aerodynamic set-up. That’s where sports engineering comes in to produce high-tech bike frames, group sets, aero bars and helmets to reduce aero-dynamic drag, and textile technology to produce skin suits to manipulate the way air flows across the cyclist’s body.

“At 20kph if you increase your power by 50watts you might increase velocity by 5kph. But riding in a time trial at 40kph, if you increase power by that same 50 watts, you might only experience an increase of 2kph. So the faster you go, the amount of increase gets smaller and smaller for further increases in power.”

Rohan Dennis, BMC Racing Team, holds the record for the fastest average speed in a Tour de France time trial - 55.446kmh. He told us: “When you watch a cycling race on TV it doesn’t look like we’re going that fast. So it’s always surprising when they show the motorbike speed in front of the lead out trains or in the sprints and we’re going 60 or 70 kilometres per hour. Even I am surprised when I watch it on television.

"When the speed is actually shown in real time for the whole race, specially going up hills when they show the percentage of the gradient, it gives a better sense of how fast we are actually riding and that it’s not as easy as it actually looks.”

Climbing at the Tour de Romandie (Tim de Waele/Corbis via Getty Images)


“Speed also is relevant in climbs,” continues Dr Dwyer. “Simply the highest speed you can produce on a climb for a sustained effort. Because the speeds are much lower than on the flatter parts, aerodynamic drag is less important. It’s not completely unimportant but it’s less important … so it’s not so important for riders to adopt aerodynamic postures on their bikes on climbs. It’s more determined by power output and steepness.

“The benefit of having a super-domestique pace their team captain up a climb is partly psychological. On really steep climbs in Grand Tours aerodynamic drag is very small. So the team captain feels supported and is fed and watered and the domestique chases down attacks … and the leader perhaps rides tempo so they’re ready to hit the next time climb and smash themselves and take the stage victory.”

Marcel Kittel on his way to a sprint victory in Limoges (LIONEL BONAVENTURE/AFP/Getty Images)


Just as a relatively heavy sprinter may lose time in the mountains, they will be faster on the flat. When most cycling fans think about outright speed, they think of the sprinters. While a specialist like Marcel Kittel (Quick-Step Floors Pro Cycling Team) must be fastest across entire stage to win, he may not need to be fastest in the final sprint. Velon’s live race data has shown the fastest rider in a bunch sprint is not always first over the line.

There are multiple factors at work, as Dr Dwyer explains.

“The final sprint is almost like a microcosm of the entire stage of a road race in that it’s about how you use a finite amount of energy in a particular period of time. It’s also about your ability to accelerate. It depends upon how the sprint unfolds, who led who out, who came off whose wheel, whether it’s slightly uphill or downhill. It’s possible that a cyclist with tremendous acceleration can win a sprint without a higher velocity than the rider in second or third. The sprint is very complex.”

So while speed it always important in a bike race, it’s not automatically the most important factor. The second or third-fastest sprinter can win the race, and the GC contender will very often be slower than many other riders on any given day. The breakaway will be travelling faster than the peloton for some of the stage – until the point when the peloton choose to reel in the breakaway.

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