By the numbers: Just how hard is the Tour of Flanders?

by Stephen Gallagher


The Tour of Flanders is regarded as one of the hardest one-day races in the world; a 260km slog over steep cobbled climbs and narrow farm roads in northern Belgium, and a race that only the very strongest riders can win. Philippe Gilbert (QuickStep Floors) was the winner of Sunday’s 2017 edition courtesy of a thrilling 55km solo move that few, including Gilbert himself, expected to succeed.

But just how hard is the Tour of Flanders? What does it take to finish ‘De Ronde’, and to finish with a respectable result? Former pro and Dig Deep Coaching co-founder Stephen Gallagher has analysed the power data of riders in the race to answer those very questions.


This post refers to the power outputs and power-to-weight ratios of the pros. To put these into context and see where the pros fit in relation to everyday riders, check out this table from Andy Coggan at the Training Peaks website.

From the start

It took less that 1km for the attacks to start, with a number of riders keen to get into the early move. A group of eight came together and worked well to quickly build an advantage over the peloton; an advantage that grew to 12 minutes at one point.

Three of the eight breakaway riders were Julien Duval (Ag2r-La Mondiale), Julien Morice (Direct Energie) and Oliviero Troia of (UAE Team Emirates). In the first 11.5km of the race, which took the leading riders around 14:30 to cover, these riders were already putting out some big numbers, even though they still had some 250km left to ride.

Julien Morice averaged 406W (5.07 W/kg) in this first 14:30, kicking out a max wattage of 1,203W (15.02 W/kg) after only 700m of racing. Oliviero Troia had similar stats: He averaged 401W (5.17 W/kg) in the first section and again had a massive max wattage at around the 700m mark with 1,370W (19.02 W/kg).

You can see from these stats that the effort and power needed to jump into the initial break is considerable. Thankfully for those that made it into the break, things settled down from there as the leaders started building a lead over the first 10-15km. Oliviero Troia covered the first 100km in 2 hours 26 minutes, averaging 302W (4.19 W/kg) and cruising at an average of 41km/h.

The difference between sitting in peloton and riding a hard tempo in the break is easily seen when comparing Julien Duval’s data with that of eventual 11th place finisher Michael Valgren (Astana) who was in the bunch. Duval rode at 249W (3.61 W/kg) in the first half of the race while Michael averaged just 178W (2.4 W/kg) — a significant difference of 1.2 W/kg between the effort needed to maintain position in the break, and the effort needed to keep out of trouble and conserve energy in the peloton.

Given the effort Duval put in, it was impressive to see that he still had the energy reserves to maintain a big effort over the final half of the race, eventually finishing 31st, only 3:30 down on Gilbert.

Into the Hills

After the first ascent of the Oude Kwaremont with 144km to go, BMC and Bora-Hansgrohe took the initiative to keep the break under control. We can see this in the data of Lukas Pöstlberger (Bora-hansgrohe) who started to apply pressure at the head of the peloton around this time.

In the section from the Kortekeer climb, with 134km to go, until the Muur van Geraardsbergen, with 95km to go, Lukas had a normalised power* of 345W (4.92 W/kg) for one hour. During this time the peloton tackled a number of climbs, all of which saw Pöstlberger put out impressive numbers:


Climb Time Power W/kg
Kortekeer 2:45 372 5.31
Eikenberg 3:39 360 5.19
Wolvenberg 1:30 417 5.96
Leberg 1:52 439 6.27
Berendries 2:23 412 5.89
Tenbosse 0:55 460 6.75

This effort was enough to cut the breakaway’s lead down to five minutes, allowing the main players to take centre stage and begin racing for the win.

The attacks start

The main moves started to happen on the Muur van Geraardsbergen with 95km to go when Boonen and his teammates applied pressure at the front of the bunch. This saw a group of 14 move clear of the peloton.

Looking at the climb times on the Muur it is easy to see why Boonen’s group gained an advantage so quickly as they crested the iconic ascent. Among those at the front of the leading group forging the split was Arnaud Démare (FDJ) who tackled the climb in 2:55. Greg Van Avermaet (BMC), one of the big pre-race favourites, missed the split after being badly positioned and completed the climb in 3:23.

The tempo was lifted both in the Boonen group of 14, which eventually swallowed up the initial breakaway, and by the riders behind the Boonen group who wanted to close the gap. Tom Van Asbroeck (Cannondale-Drapac) kept a good position in the chasing group and needed some solid power to do so.

Over the 35km from the Muur to the second ascent of the Oude Kwaremont, Van Asbroeck had a normalised power of 350W (5.07 W/kg). This is after 170km and 4 hours 15 minutes of racing. On the climb of the Kanarieberg, after 189km, Van Asbroeck averaged an eye-watering 460W (6.66 W/kg) for the 2:47 it took him to pass over the climb.

Bridging to the leaders

The pace was on over the Kanarieberg, Oude Kwaremont and Paterberg as the Greg Van Avermaet/Peter Sagan group tried to regain contact with the Boonen group. Among those trying to bridge across was Michael Valgren. Valgren produced his peak two-minute power on the Koppenberg climb with 44km to go, pushing out 509W average (6.88 W/kg). Over the next 31km and 46 minutes, as the group passed over the final climbs (and as Gilbert was out front trying to hold onto his lead), Valgren had a normalised power of 365W (4.93 W/kg)

For context, the 4.93 W/kg that Valgren produced is the sort of power that many cyclists of A-grade or B-grade level could sustain for roughly 20 minutes, normally from a fresh state. Valgren produced this same power for more than twice as long (46 minutes), and all after 230km and 5 hours and 40 minutes of racing. Impressive stuff to say the least.

Here’s a look at what Valgren produced over the final climbs:


Climb Time Power W/kg
Steenbeekdries 1:41 366 4.95
Taaienberg 1:41 481 6.5
Kruisberg 3:46 434 5.86
Oude Kwaremont 4:22 444 6.00
Paterberg 1:19 522 7.05

Quite simply: In order to be a contender at the Tour of Flanders, you need to be able to do repeated efforts of 6-7 W/kg for anywhere between 90 seconds and four minutes, and all with six hours of racing in your legs.

Final stats

In order to finish 11th at the Tour of Flanders, 53 seconds behind Gilbert, here’s what was required of Michael Valgren:

Time: 6 hours 24 minutes
Distance: 260km
Normalised power: 310W
Power-to-weight ratio: 4.18 W/kg

And here’s what a couple other riders had to produce:

Impressive numbers and another reminder of just how strong the pros truly are.

*To understand what normalised power is and how it differs from average power, this explanation at Training Peaks is worth reading. In short: normalised power “is an attempt to better quantify the physiological ‘cost’ of the harder ‘feel’ of the variable effort.”
 
The graphics in this post appear courtesy of VeloViewer and Philipp Diegner.

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