Today’s Il Lombardia will be decided in the last twenty-one kilometres, on two climbs. The Civiglio: 4.2 km at 9.7%, cresting 16.7 km from the finish. The San Fermo della Battaglia, second time up: 2.7 km at 7.2%, cresting 5.2 km from Como. In between and afterwards, only descents and the lakeside road.
Whoever wants to arrive alone, whether it is Isaac Del Toro, Remco Evenepoel or anyone else, has one question: where to go? The answer depends on two numbers, and physics can work them out. How much you gain on a climb with a few more watts than the others. And how much the chasers can take back after the top.
What an attack on a climb is worth
| Extra watts | At the top of the Civiglio | At the top of the San Fermo |
|---|---|---|
| +3% | 22″ | 10″ |
| +5% | 36″ | 17″ |
| +8% | 56″ | 26″ |
On the Civiglio every extra percentage point of power is worth about seven seconds, on the San Fermo about three and a half. The Civiglio is steeper and longer: riders climb it at 17.6 km/h, air resistance barely matters and watts per kilo are everything. It is where legs make the biggest difference.
How much the chasers can take back
Against a single chaser riding at the same power, nothing comes back: every second gained on the climb stays until the finish. Against two riders sharing the work, it does. In the slipstream the air costs a third less, and on the flat two chasers ride at 42.8 km/h against 40.2 km/h for a rider alone.
From the top of the San Fermo to the finish there are 5.2 km, almost all downhill. Even if they were all flat, two chasers would take back 28″ at most. From the top of the Civiglio there are 14 km away from the climbs: counting them all as flat, up to 75″.
So
On the San Fermo the margins are tight. With 8% more watts for seven and a half minutes you reach the top with 26″, just under what two cooperating chasers can take back. But if the chasers do not work together, or one of them is a team-mate who will not pull, ten seconds are enough.
On the Civiglio an attack is worth twice as much: with 8% more it is 56″ at the top. Against two chasers in perfect agreement for 14 km, it may not be enough. But over 14 km chasers rarely share the work evenly, and the rider in front picks his own lines on the descents.
Whoever has the best sprint in a small group can wait for the San Fermo. Whoever has to arrive alone has only one place: the Civiglio. Tonight, after the finish, we will put the numbers next to what happened.
How we did the maths
The climbs and distances come from the organiser’s race schedule and climb profiles. The rest is the physics of cycling power: gradient, weight, air and rolling resistance. The assumptions, the same for everyone: a 62 kg rider and an 8 kg bike; on the climbs the chasers push 6 watts per kilo, after 220 km of racing, and 4.6 between the climbs; a frontal area (CdA) of 0.36 m² on the climbs and 0.30 on the flat; in the slipstream the air costs 35% less. On the descents we count neither gains nor losses: bike handling decides. It is not a prediction: the numbers change with the assumptions, the comparison between the two climbs does not. The maths and the text were done by artificial intelligence, following the rules of la fagIAnata.
Written with the help of Mnemosyne.