Hirnant Pass: Cycling Climb

The climb · United Kingdom

About Hirnant Pass

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Simon Warren’s Another 100 Greatest Cycling Climbs

On the Bala side of Hirnant Pass, the longer valley approach eventually gives way to a much firmer climb towards the crest. The recorded ascent picks up this final section, already high in Cwm Hirnant, rather than starting in Bala itself. Over 1.8 kilometres it gains about 150 metres. The widening valley and open slopes make the remaining height easy to see, even when the road's changing gradient makes it harder to judge the effort still required.

The opening is comparatively measured, but the climb soon becomes more demanding. Successive stretches vary in steepness without providing a meaningful flat section, and the upper road continues to ask for work. A corner or a softer patch should not be mistaken for the end. The exposed valley setting gives this short ascent a bigger feel than its length suggests. Hirnant is a proper concluding climb after the approach, with enough variation to keep a steady effort interesting.

01 / The ascent

Elevation profile

Start 355 m · Summit 503 m

Gradient by distance1.82 km / 148 m gain

0 km0.4 km0.7 km1.1 km1.5 km1.8 km

02 / The numbers

Climb statistics

Distance: 1.82 km
Elevation gain: 148 m
Average gradient: 8.1%
Climb category: 4
Start elevation: 355 m
Summit elevation: 503 m

Current weather

At the climb start

Loading weather…

Weather data: MET Norway

03 / Your effort

How long would it take?

Enter the power you could hold for the whole climb. We calculate a moving time from the elevation profile and the forces you ride against.

Sustained power

W/kg

Use your intended climbing effort, rather than FTP unless you can hold it for the predicted duration.

Rider weight (kg)

Bike + kit weight (kg)

Bike + kit includes clothing, bottles and luggage.

Advanced settings

Defaults represent a road-bike scenario. Adjust these settings to match your tyres, drivetrain and riding position.

Effective drag area (CdA) (m²)

Rolling resistance (Crr)

Drivetrain efficiency (%)

Modelled moving time

10 min

Power throughout: 225 W
Average speed: 10.9 km/h

Based on the 1.82 km elevation profile. Assumes steady power, with no stops, braking or drafting. Rounded to the nearest minute.

The science behind the calculation

For each part of the stored profile, we solve the steady-state cycling power equation for speed, then add distance ÷ speed across the climb. Gravity uses rider + equipment weight; available power is W/kg × rider weight. This uses the profile’s distance and elevation together, without mixing in another route’s metrics.

Power × efficiency = gravity + rolling resistance + air resistance + bearing losses

The resistance equations are adapted from Martin et al. (1998), Validation of a Mathematical Model for Road Cycling Power. Air density changes with profile altitude using NASA’s standard-atmosphere model. This calculator’s adaptation has not been independently validated.

It predicts travel at the power you enter, including on descents. It does not model acceleration, cornering, braking, traffic, wind, changing weather or fatigue. At altitude, choose power you can sustain there: thinner air reduces drag, but this model does not predict its effect on your ability to produce power. Profile quality and assumed equipment settings also affect the result.

04 / On the ground