Will the breakout survive? Chapatte’s law could have the answer

The flat stages of professional men’s cycle races often follow a similar scenario. At the start, a breakaway will go up the road and be an advantage of a few minutes or more – depending on how much rope the peloton wants to provide. Then at some point the peloton will start pulling on that rope, gradually winding up the breakaway before a sprint finish.

Most of the time, the peloton times the pursuit perfectly. The breakaway is caught a few kilometers from the end and the pace is high enough that further attacks are not possible. But sometimes the peloton leaves too much room for the breakaway and / or leaves the chase too late. On these rare occasions, the breakaway wins.

So how much rope is too much rope? How can sprinter teams – and for that matter those of us watching at home – tell if a breakaway will go the distance? Chapatte’s law can help you.

Chapatte’s law?

Robert Chapatte was a French cyclist who raced professionally in the 1940s and 1950s before becoming a radio and television commentator.

Chapatte’s theory, based on his experience as both a runner and commentator, was that a pursuit peloton would need 10km to close a one-minute gap with a lone leader. A gap of more than a minute meant the lone leader would survive. Anything less and the peloton would catch up in time. This rule could then be extrapolated to two minutes at 20 km, three minutes at 30 km, and so on.

By now you will hear TV commentators refer to Chapatte’s Law, if not by name, then certainly by the fact that the breakaway will need a one-minute gap with 10km to go.

It should be obvious that this is anything but a hard rule. There are a multitude of variables that can determine if a minute is enough for the breakaway 10 km from the finish.

Terrain and roads

Chapatte’s law is best applied on flat sprint days without too much climbing. The ups and downs introduce a multitude of variables into the mix.

How much escalation is there? Are the sprinters’ servants able to maintain the tempo necessary to catch up with the break while tackling each climb of the course? are the sprinters able to? It’s no coincidence that most breakaway wins happen on the roughest days.

The uphill or downhill finishes take things to another level. A group of chasers (often greatly reduced in number at this stage) can save much more time on an uphill finish (some estimates suggest up to two minutes over 10 km).

The reverse is probably true for a downhill finish. The peloton is unlikely to gain time on a smaller group on the descent, especially if the descent is technical.

The nature of the roads can have an impact even on flatter stages. On wide and straight arrivals, the peloton has an advantage. If the last few kilometers are on narrow roads with a lot of bends and bends, where positioning is tricky in the peloton, the breakaway could take a little less time.

Nature of the escape

Of course, the size and composition of the breakaway also play a role.

Chapatte believed that a lone runner one minute ahead with 10 km to go was more likely to survive than a larger breakaway. His reasoning was that large groups are prone to a lack of cooperation in the last kilometers; that runners tend to attack each other late (those who don’t support each other in a sprint, say) and watch each other for such attacks. In doing so, they reduce the consistency and force of the effort they put in to maintain a lead.

A lone rider has no such worries. They have no choice but to commit 100% to the end.

Chapatte’s reasoning is solid, but the reverse could also be true. If an escape is engaged long enough, that means more riders share the load, sharing the time in the wind.

Again, it is not clear.

Nature of the peloton

The nature of the peloton is also a factor. How many teams have signed up to chase the breakaway? Just one? Five? And how many runners do these teams engage in the hunt?

Is it just the sprinting teams up front? Or do GC teams also contribute?

A more concerted pursuit will only increase the chances of the peloton. If it’s just a team trying to take a break, that could be a different story.

Modern cycling

It is worth reiterating that Chapatte’s law is well over half a century old. Road cycling has come a very long way during this time. Teams are more professional than ever, sprint trains are more organized than ever, and many teams employ runners specifically to control and chase breakaways.

What is the result of this? Well, some have speculated that nowadays it is more likely that a peloton can close up to 90 seconds in 10 km, rather than a minute. Anecdotal evidence seems to support this theory – this week in Stage 4 of the 2021 Tour de France, solo leader Brent Van Moer (Lotto Soudal) was one minute ahead with just 8km to go. The Belgian was caught just before the line. During the extraordinary Amstel Gold Race 2019, a pursuit group led by Mathieu van der Poel apparently closed its doors for one minute in the space of just 3 km.

These are just two examples. To make a convincing revision to Chapatte’s law, more data would be needed.

A useful framework

It should be clear by now that Chapatte’s law is anything but clear. As in all facets of cycling, there are so many variables that determine if this “law” is true in any given case, all these years later. It should also be noted that this law was initially proposed in the context of men’s races. Whether this is true in women’s cycling – where the dynamics of race, team and peloton are significantly different – is not clear.

In the context of high-level men’s races like the Tour de France, however, “one minute per 10 km” has a nice resonance. Decades after the creation of Chapatte’s law, it remains a relatively useful baseline measure for quickly assessing the progress of a bicycle race.