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How to read these numbers

Why every maximum states a distance

The gradient of a road depends on the distance you measure it over. The same hill can honestly be 32% over 2 m, 29% over 5 m and 25% over 100 m — all three at once. A “maximum gradient” without a distance is unfalsifiable, which is why signs, cycling databases and GPS platforms so often disagree: they are answering different questions. Every value here is a window maximum: the steepest stretch of exactly that plan-distance anywhere on the climb.

Why 2 m and 3 m are “diagnostic”

A window gradient is computed from two terrain samples, so elevation noise propagates as σ ≈ √2 × σ_elev / window. With roughly ±10 cm per sample (the source surveys quote ±15 cm RMSE), the raster-noise uncertainty alone is:

At 2 m the noise is as large as the differences being claimed, and the systematic errors are worst there too: a metre of centreline placement error moves the line onto road camber or verge, and interpolation smooths features shorter than about two raster cells. There is also a physical point — 2 m is shorter than a bicycle’s wheelbase, so no vehicle experiences a 2 m gradient as a gradient.

We publish 2 m and 3 m values anyway, greyed and labelled diagnostic, because that is where headline claims live: gradient signs, platform “max grade” figures and record adjudications typically match the 2–10 m scale. Diagnostic windows exist to interpret those claims. They are never used in rankings.

Quality interventions

Three tiers, in increasing force — raw data is never modified:

≈ the surface model sits well above the terrain along this window (tree canopy, walls, buildings), so the bare-ground model there is built from fewer laser returns: the value stands but is less certain — rankings and ladders mark it with ≈.
excluded the window crossed ground where the terrain model does not represent the road — a physical discontinuity, a mapped bridge/tunnel, or dense plantation whose cross-sections show no road bench at all (the surveyed “ground” there is canopy): the maximum shown is the steepest clean stretch and the displaced raw reading is noted.
needs review the final numbers still trip plausibility checks and await human scrutiny.

What “Known from” means

Recognition and documentation are different things, and the catalogue separates them:

Listed — the climb appears on an external list we record (books, championship venues, race routes), cited by numbered footnote. Membership facts only: we never copy a list’s own measurements.
sign: 32% (2025) — a physical gradient sign observed on the road, with the year of the observation. Signs get repainted (one of our climbs went 25% → 32% between observations), so the date is part of the fact.
tag: 25% (2026) — an OpenStreetMap incline value or mapper estimate, dated by the map snapshot we read it from. Weaker evidence than a sign: usually right, but some tags are impressions rather than sign readings — our measurements test them either way.
— — on no list we know of: an unlisted find of this survey.

Seen a sign we don’t show, or one that has changed? Report it with a photo — on-the-ground observations outrank everything here.

What these numbers are not

They are terrain-model measurements along the mapped road centreline — not asphalt surveys. Field validation with an inclinometer is part of the programme; until a climb has it, treat short-window values as estimates with the uncertainties above.