How Are Climbs Categorised?

The Tour de France tackles the hors catégorie Col du Tourmalet today for the 81st time. The race rates climbs with five labels, from 4th category for the easiest to 1st category and then HC for hors catégorie, “beyond categorisation”. A frequently asked question is how are these categories determined. Here’s the answer…



The categories serve two purposes:

To illustrate the difficulty of the climb for the riders media and spectators

To set the number of the points awarded for the mountains competition

These ratings are set by the Tour de France and not by any mapping company or military survey. There is a formula to classify the climbs where you take the square of the slope’s % gradient and multiply it by the length in kilometres to get a score:

%2 x km

At the risk of reading like a school maths book here are some examples:

The HC-rated 17.1km Col du Tourmalet sits at 2,115m above sea level and starts at 860m, a slope of 7.3%. That’s 7.3 2 x 17.1 = 911

x 17.1 = 911 Tomorrow’s Plateau de Beille summit finish, also HC-rated, is 7.9% and 15.8km long = 986

The highest score in the race this year is the Col de la Croix de Fer, 6.9% for 22.4km = 1066

The south side of the Col du Glandon, used on Stage 18, is HC-rated and 5.1% from 21.7km = 564

Next week’s summit finish at La Toussuire is a 1st category climb and with 6.1% for 18km scores 670

Alpe d’Huez is 8.1% for 13.8km = 905

So how come the Glandon scores 564 yet is HC-rated compared to the 1st category La Toussuire which scores 670 ? It’s because the average gradient doesn’t tell us everything. Look at the profile for the Glandon’s south side:

The Glandon’s got two downhill sections, each roughly two kilometres long and these reduce the mean average slope. For the cyclist the mode gradient is roughly 7% for 17km which makes it harder than La Toussuire, is 6.1% for 18km.

The formula is used for information not definition. You know an HC climb when you see it and you can work backwards to rate a first category climb. The more arbitrary definitions go to the smaller climbs were sometimes a tiny rise in the road is labelled as a climb in order to spice up a stage and ensure the sponsors get some value for their spend. Sometimes the race owners just want to enliven part of the stage and tilt the incentives.

“These go to HC”

Humans have discovered distant planets and classified hundreds of thousands of species of animals but there are some climbs that are apparently beyond categorisation. Rather than having climbs rated from 1st to 5th category, we have the hors catégorie label, as in “beyond classification” presumably because it sounds better, a dash of mystery and adventure. The Tourmalet has been climbed for over 100 years, long before the category system arrived. So HC label has a touch of the Spinal Tap hype but all the same these are exceptional roads.

Summary

There is a formula but there is no fixed rule, the categories are applied according to common sense to help distinguish a climb’s value, a rating of the difficulty but also its strategic importance.