Portezuelo de Chaxas

Portezuelo de Chaxas cycling climb profile

Portezuelo de Chaxas is an HC climb in Chile, and the numbers explain why it demands respect before the first pedal stroke. The climb runs for 21.6 km at an average gradient of 7.79%, starting at 2951 m and topping out at 4631 m. That is a long, sustained effort with very little room for pacing errors, especially because the maximum gradient reaches 12.23%.

The defining feature is the combination of length, steepness, and elevation. A climb averaging almost 8% for more than 20 km is not just a muscular test. It is a control problem. Ride the early kilometres too close to threshold and the upper section becomes a slow collapse rather than a manageable grind.

How the gradient shapes the ride

With a listed average of 7.79%, Portezuelo de Chaxas should be approached as a steady, high-load climb rather than a rolling pass where short recoveries reset the legs. The maximum gradient of 12.23% matters because it means the average does not tell the full story. Even if much of the climb sits near a sustainable tempo, there are steeper sections that will push cadence down and force torque up.

That changes the tactical feel of the climb. The risk is not one isolated ramp. The risk is repeatedly over-spending on the steeper pitches while already carrying the fatigue of a long ascent. On a climb of 21.6 km, those small spikes compound. Every surge above your sustainable climbing power has to be paid back later, and the summit comes high enough that recovery will not feel as generous as it does lower down.

Pacing strategy

The best pacing model is conservative early, stable through the middle, and only opportunistic late. For riders using power, this is a climb to anchor below /glossary/ftp at the start rather than riding the average gradient as if it were a short hill. Heart-rate riders should expect drift, particularly as the climb rises from 2951 m to 4631 m, so chasing an early number can be misleading.

A practical approach:

• Start with a gear that feels slightly too easy.
• Keep pressure smooth on the pedals through the sustained sections.
• Treat any ramp near the maximum gradient as a cadence-management problem, not a place to attack.
• Save the hardest effort for the final portion, once the remaining distance is no longer the main limiter.

If you are estimating target power beforehand, use a realistic climbing number rather than a fresh short-effort benchmark. The /tools/ftp-estimator can help set the ceiling, but the pacing target should account for the climb's duration and altitude profile.

Gearing notes

Portezuelo de Chaxas rewards low gearing. The average gradient is already demanding, and the 12.23% maximum means a standard climbing setup can quickly feel over-geared if fatigue or altitude starts to bite. The goal is to preserve cadence before you need it, not after the legs have already loaded up.

Choose gearing that lets you stay seated on sustained 8% terrain while still having a bailout gear for the steepest ramps. If the easiest gear is only comfortable when fresh, it is probably not easy enough for this climb. On Portezuelo de Chaxas, the right setup is the one that lets you keep the effort aerobic for as long as possible, because once the climb starts taking repayments, there are still a lot of metres left to gain.