Col du Las

Overview

Col du Las is a Category 3 climb in France, running 10.7 km from a start elevation of 378 m to a summit at 720 m. Its net elevation gain is 342 m, and with an average gradient of 3.2% it reads, on paper, as a moderate mid-length ascent. For a rider scanning the numbers, it looks like a steady tempo effort rather than a leg-breaker.

The paper reading is incomplete. The total ascent is 510 m, well above the 342 m of net gain — a gap of 168 m spent climbing terrain you later give back on the descents in between. That undulation means the real climbing is packed into a smaller share of the route than the length suggests, so the pitches that count are steeper and more frequent than the 3.2% average implies. Budget your effort for those ramps, not the average.

How the Gradient Unfolds

The 3.2% average is diluted by flat and downhill sections; it does not describe any single stretch of road. The steepest ramp hits 12.9%, roughly four times the average, and the effort lives in these short, sharp pitches rather than in a smooth grind. Expect to shift gears often.

• Flatter and false-flat sections where you can recover and carry speed
• Short descents that force you back onto the pedals afterward
• Repeated punchy climbs stacked through the middle of the profile
• A steepest ramp of 12.9% that demands your lowest gear

Pacing Notes

On a climb this undulating, even-effort beats even-speed. Chasing a constant speed forces you to over-power the steep pitches and coast the flats, spiking your heart rate exactly where it hurts most. Instead, hold a steady sustainable power output and let your speed rise and fall with the gradient — faster on the false flats, slower on the 12.9% ramps.

Do not empty yourself on the early pitches; the repeated climbs punish riders who start too hard. If you are unsure what number to hold, run the FTP estimator first and pace to a sensible fraction of it across the whole 10.7 km.

Gearing

The 12.9% maximum gradient governs your setup. A compact (50/34) or sub-compact chainset paired with a wide-range cassette will keep your cadence up on the steepest ramp without grinding. A 34×32 handles it for most riders; 34×34 gives extra margin if you fatigue on the repeated pitches or ride at higher weight. Check your chainset and cassette before the ride — the steep sections are short, but they are exactly where the wrong gear costs you.

Summary

• Length: 10.7 km
• Average gradient: 3.2%
• Maximum gradient: 12.9%
• Net elevation gain: 342 m
• Total ascent: 510 m
• Category: 3

Col du Las rewards riders who read past the 3.2% average. Pace to steady effort, gear for the 12.9% ramps, and treat the 168 m of extra ascent as the real story of the day.