Bwlch-y-Clawdd Road
4804.4 m · net rise 269.9 m · total ascent 272.0 m · overall 5.6% · evidence quality A (high) · Treorchy · Mid Glamorgan · share
Shape: sustained — 30% of the climbing sits in a quarter of the distance.
Matches: 100 Greatest Cycling Climbs (Simon Warren) — The Bwlch, #99 — which of the three sides Warren describes is unreviewed against our route — No. 99, as "The Bwlch" — the Rhondda climb (official app, 2026 numbering).
Gradient ladder what do windows mean?
| Window | Maximum | Located at | |
|---|---|---|---|
| 2 m (diagnostic) | 17% | 1844–1846 m | |
| 3 m (diagnostic) | 12% | 1844–1847 m | |
| 5 m | 10% | 2013–2018 m | |
| 10 m | 10% | 1955–1965 m | |
| 20 m | 8.9% | 1954–1974 m | |
| 25 m | 8.9% | 2009–2034 m | |
| 50 m | 8.5% | 1992–2042 m | |
| 100 m | 8.4% | 1945–2045 m |
Measured on the mapped road line; moving the line 1 m either way reads 8.8–10.3% over 25 m.
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.
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_5_293194_20201224dtm.tif, wg_del_5_293195_20201224dtm.tif, wg_del_5_293196_20201224dtm.tif, wg_del_5_294194_20201224dtm.tif, wg_del_5_294195_20201224dtm.tif, wg_del_5_294196_20201224dtm.tif, wg_del_5_295194_20201224dtm.tif, wg_del_5_295195_20201224dtm.tif, wg_del_5_295196_20201224dtm.tif |
| Road centreline | OpenStreetMap (local PBF extract), snapshot 2026-08-10T20:21:40Z |
| Quality status | evidence quality A; no review flags; no caveated windows |
| Analysis | OCL 0.1.0, analysis 0.1.0, run identifier not recorded (legacy measurement, before the campaign driver stamped runs), calculated 2026-08-12 |
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_5_293194_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_293195_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_293196_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_294194_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_294195_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_294196_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_295194_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_295195_20201224dtm.tif",
"data/cache/wales/dtm_1m/wg_del_5_295196_20201224dtm.tif"
],
"calculated_at": "2026-08-12T09:06:20+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",
"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_5_293194_20201224dtm.tif",
"wg_del_5_293195_20201224dtm.tif",
"wg_del_5_293196_20201224dtm.tif",
"wg_del_5_294194_20201224dtm.tif",
"wg_del_5_294195_20201224dtm.tif",
"wg_del_5_294196_20201224dtm.tif",
"wg_del_5_295194_20201224dtm.tif",
"wg_del_5_295195_20201224dtm.tif",
"wg_del_5_295196_20201224dtm.tif"
],
"elevation_capture_dates": [
"24-12-2020"
],
"climb_origin": "discovered",
"license": "ODbL-1.0",
"license_url": "https://howsteep.org/licensing"
}