Llanberis Pass Pen-y-Pass: Cycling Climb

The climb · United Kingdom

About Llanberis Pass Pen-y-Pass

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Simon Warren’s Another 100 Greatest Cycling Climbs

From Nant Peris, the road to Pen-y-Pass follows the rocky corridor of the Llanberis Pass. Boulders and steep mountain sides give the ascent its scale, while the road itself initially climbs with relative restraint. This western approach covers just under five kilometres and gains about 250 metres. It begins well up the valley, so the ride from Llanberis village is an approach to the recorded ascent rather than part of its stated length.

The gradient strengthens as you work farther into the pass. The middle section takes more effort than the opening, and the final stretch continues that firmer climbing towards Pen-y-Pass. There is room to find a rhythm, but assuming the whole road will feel like its lower slopes leaves work unpaid at the top. The finish is the road pass, with the mountains still towering above it. This is a sustained ascent made memorable by the surrounding rock rather than a single severe ramp.

01 / The ascent

Elevation profile

Start 110 m · Summit 362 m

Gradient by distance4.96 km / 252 m gain

0 km1 km2 km3 km4 km5.0 km

02 / The crux

Where it gets difficult

Choose a distance to find the steepest continuous section of the climb.

Steepest 500 m average

8.8%

Where to find it

4.30–4.80 km from start

Net height gained: 44 m
Section length: 500 m

The whole climb4.96 km

0 kmFinish

03 / The numbers

Climb statistics

Distance: 4.96 km
Elevation gain: 252 m
Average gradient: 5.1%
Climb category: 3
Start elevation: 110 m
Summit elevation: 362 m

Current weather

At the climb start

Loading weather…

Weather data: MET Norway

04 / 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

19 min

Power throughout: 225 W
Average speed: 15.6 km/h

Based on the 4.96 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.

05 / On the ground