Lane near Dolgarrog°
665.7 m · net rise 148.9 m · total ascent 149.6 m · overall 22.4% · evidence quality B (good) · Dolgarrog · Clwyd · share
Shape: sustained — 33% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 466 m.
Matches: BikeRadar, "7 of the steepest UK climbs, ranked" — Listed by BikeRadar as Afon Ddu, Conwy Valley — independent corroboration of the survey's machine-found UK-steepest (36.6% over 25 m); established-name candidate pending the identification-certain check.
° The name is provisional: this climb is not yet matched to a documented name, so it was named from nearby map places. There is no evidence of local usage — (auto-named from gazetteer; was discovered-street-53-1793-3-8400). Corrections welcome.
≈ Overhead cover (tree canopy or structures) spans 75% of this route — detected by comparing the surface model (DSM, treetops and rooftops) against the terrain model (DTM, bare ground). Under cover the bare-ground model is built from fewer laser returns, so metre-scale readings can wobble; maxima whose window sits in a covered zone are marked ≈ below — less certain — the flag does not say whether the true value is higher or lower. Longer windows average over more clean ground and are steadier.
Gradient ladder what do windows mean?
| Window | Maximum | Located at | |
|---|---|---|---|
| 2 m (diagnostic) | ≈46% | 147–149 m | under overhead cover terrain reads 66.3% at 452–454 m across a structure — excluded |
| 3 m (diagnostic) | ≈41% | 500–503 m | under overhead cover terrain reads 66.3% at 451–454 m across a structure — excluded |
| 5 m | ≈40% | 499–504 m | under overhead cover terrain reads 56.3% at 451–456 m across a structure — excluded |
| 10 m | ≈39% | 494–504 m | under overhead cover terrain reads 44.0% at 445–455 m across a structure — excluded |
| 20 m | ≈37.0% | 484–504 m | under overhead cover terrain reads 38.1% at 440–460 m across a structure — excluded |
| 25 m | ≈36.6% | 479–504 m | under overhead cover terrain reads 36.7% at 440–465 m across a structure — excluded |
| 50 m | ≈34.7% | 458–508 m | under overhead cover terrain reads 36.3% at 451–501 m across a structure — excluded |
| 100 m | ≈27.4% | 458–558 m | under overhead cover terrain reads 32.2% at 421–521 m across a structure — excluded |
Measured on the mapped road line; moving the line 1 m either way reads 36.8–38.7% over 25 m.
may start earliermay continue beyond end Extent detection suggests reviewing where this climb starts/ends.
Map
Check this route yourself: Google Maps route via their router · Street View at the base where coverage exists · geojson.io our exact measured line · OpenTopoMap
No aerial layer here: Britain has no open or government source of aerial photography at road scale — the pan-government APGB imagery is licensed to the public sector only, unlike the LiDAR this survey is measured from. Street View, where it exists, is the visual check.
This climb's data: OCL JSON — the full gradient ladder, quality flags and provenance in the OpenClimb Ladder format.
Access: Listed 2026-09-11 (record-class scrutiny, Peter): this page's steepest 25 m meets or exceeds the Baldwin Street mark (34.8 %). A figure that would beat the recognised records is treated with special scepticism: it stays out of the rankings until a person has passed it on the aerial, the road authority's line and the detector battery, as Ffordd Pen Llech and one Welsh lane were.
Measured, not vetted. This page records what the laser record shows about the road's shape — nothing more. Nobody has necessarily ridden or inspected this road for the survey, and a page here is not a recommendation and no guarantee that the road is open, surfaced, rideable or safe. Gates, private sections, missing rights of way and hazards do not show up in elevation data. Check access and conditions on the ground and make your own judgment.
Ridden it, or know better? Submit data for this climb no account needed · Share this climb
Route colour = gradient over a 25 m window: <10% 10–20% 20–25% ≥25%
© OpenStreetMap contributors · topo tiles © OpenTopoMap (CC-BY-SA) · vector tiles OpenFreeMap
Profile
The profile and gradient chart share one position — move your pointer over them and the marker follows. Colors are the gradient bands; the shaded span is the steepest 25 m. Any 25 m figure is good to about a point either way (why).
Measurement card
| Elevation | Welsh Government — Welsh Government LiDAR 1m DTM (2020-2023) |
|---|---|
| Resolution / CRS | 1.0 m grid, EPSG:27700; sampled every 1.0 m, bilinear interpolation |
| Tiles | wg_del_29_277366_20220319dtm.tif |
| Road centreline | OpenStreetMap (local PBF extract), snapshot 2026-08-10T20:21:40Z |
| Quality status | evidence quality B; caveated windows: canopy or structure, structure excluded |
| Analysis | OCL 0.1.0, analysis 0.1.0, run chains-wales-pilot-260827, calculated 2026-08-27 |
Provenance
{
"analysis_version": "0.1.0",
"sample_interval_m": 1.0,
"interpolation": "bilinear",
"smoothing": "none",
"gradient_windows_m": [
5.0,
10.0,
20.0,
25.0,
50.0,
100.0
],
"diagnostic_windows_m": [
2.0,
3.0
],
"elevation_crs": "EPSG:27700",
"elevation_resolution_m": 1.0,
"elevation_tiles": [
"data/cache/wales/dtm_1m/wg_del_29_277366_20220319dtm.tif"
],
"calculated_at": "2026-08-27T06:14:00+00:00",
"road_source": "OpenStreetMap (local PBF extract)",
"road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
"osm_pbf_path": "data/cache/pbf/wales-2026-08-11.osm.pbf",
"osm_snapshot": "2026-08-10T20:21:40Z",
"run_id": "chains-wales-pilot-260827",
"elevation_provider": "Welsh Government",
"elevation_dataset": "Welsh Government LiDAR 1m DTM (2020-2023)",
"elevation_licence": "Open Government Licence v3 \u2014 \u00a9 Crown copyright Welsh Government",
"elevation_catalogue_layer": "geonode:welsh_government_lidar_tile_catalogue_2020_2023",
"elevation_tile_ids": [
"wg_del_29_277366_20220319dtm.tif"
],
"elevation_capture_dates": [
"19-03-2022"
],
"climb_origin": "discovered",
"naming_note": "auto-named from gazetteer; was discovered-street-53-1793-3-8400",
"license": "ODbL-1.0",
"license_url": "https://howsteep.org/licensing"
}