Bwlch y Groes
1213.5 m · net rise 188.2 m · overall 15.5% · confidence: high · Cwm Cerddin · Gwynedd · share
Shape: sustained — 31% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 989 m.
Matches: Wikipedia, 100 Greatest Cycling Climbs (Simon Warren) — Bwlch y Groes — articles in English and Welsh; the route passes 9 m from the pass point. Wales's highest public road pass ("Hellfire Pass"). — No. 91 (verified in the official 100 Climbs app, 2026 numbering).
Gradient ladder what do windows mean?
| Window | Maximum | Located at | |
|---|---|---|---|
| 2 m (diagnostic) | 35% | 451–453 m | |
| 3 m (diagnostic) | 32% | 451–454 m | |
| 5 m | 31% | 451–456 m | |
| 10 m | 26% | 447–457 m | |
| 20 m | 24.0% | 364–384 m | |
| 25 m | 23.8% | 366–391 m | |
| 50 m | 22.8% | 353–403 m | |
| 100 m | 21.7% | 357–457 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
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.
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© OpenStreetMap contributors · topo tiles © OpenTopoMap (CC-BY-SA) · vector tiles OpenFreeMap
Profile
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_22_291322_20220114dtm.tif",
"data/cache/wales/dtm_1m/wg_del_22_291323_20220114dtm.tif"
],
"calculated_at": "2026-08-12T09:09:05+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_22_291322_20220114dtm.tif",
"wg_del_22_291323_20220114dtm.tif"
],
"elevation_capture_dates": [
"14-01-2022"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 21.4% over 200 m (Terrain 50), gain 122.4 m over 719 m way. EXTENDED by graph walk: +0 segment(s) at base, +1 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting. ADOPTED (notable slice 2026-08-11): clean-steep. AUTO-NAMED from gazetteer (hypothesis, unreviewed): was 'Discovered lane (52.7897, -3.6136)'.",
"renamed": "2026-08-13: 'Bwlch y Groes' adopted over auto-name 'Craig Y Pant to Foel Y Groes' \u2014 identification-certain (9 m from Wikidata pass point; en+cy Wikipedia); standing policy per Peter",
"license": "ODbL-1.0",
"license_url": "https://howsteep.org/licensing.html"
}