Race Rule #2: Walden says: “Shift down at the bottom of the hill, Shift up before the top!” Translation: always, (always!) “be in the right gear.” Another shouted Waldenism full of meaning.
1) shifting under massive torque results in mechanical failures (translation – shifting while pedaling hard may result in dropping, breaking or tangling your chain)
2) The human body is most efficient for certain efforts at a certain RPM. Generally speaking, maximal acceleration and power output comes from high RPM’s (115Rpm+), and efficiency comes from lower (but consistent) RPM’s (70 – 115 Rpm’s). Walden believed (as do I) that steady state efforts are best between 105 and 110 RPM's and specifically noted 107 as the magic number. Exactly to this point, after Walden passed, Chris Boardman set the world hour record with an average RPM of 107.
Walden was a total genius...
The Art: Always being the right gear means knowing the demands of the race at any given time. Uphills require acceleration of mass up the hill – hence “shift down” (smaller gear, higher rpm). Downhills are a chance for efficiency and rest – hence “shift up” (bigger gear, slower rpm) – not to mention the rotational inertia of two muscle laden legs weighing 70+ pounds, when slowing from 150Rpms to 70 Rpms provides extra inertia to the pedals without an extra ounce of energy.
Then there is the rest of the race… which follows similar patterns.
- Always downshift prior to a short hill – into your small chainring if required – BEFORE applying torque
- Always upshift right before the top of the hill (not when heading down) – use that rotational energy and the efficiencies of that motion to start recovering early
- Subtle note – I always time my downshifting for when my left leg is nearing the top of its stroke, and my upshifting (larger gear) for when my right leg is nearing the top of the stroke. I didn’t even realize the physics of it, but this assures that during the maximal torque associated with each down cycle of the pedal stroke, the flex from the torque on the crank arm aligns with the direction you want the chain to be pulled.
- Always downshift prior to corners (and pedal once to make sure you are in gear) I think more “last corner” crashes are due to this failure (shifting midway through the corner, then cranking hard, skipping a gear, causing slippage) than any other maneuverings.
- In the final laps of the race, always ride in a smaller gear. Taking advantage of opportunities to move up without spending time “in the wind” requires instant accelerations to “fill the gaps”. In the last few laps of any given criterium, I generally ride between 115 – 125 rpms, and ride with both hands clenching the brakes – to take advantage of internal opportunities to move up in the draft, while at the same time using my brakes to keep safe.