Bignor Down
1873.8 m · net rise 162.3 m · total ascent 165.9 m · overall 8.7% · confidence: good · Sutton · West Sussex
Shape: stepped — 45% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 214 m.
Found purely from mapping and LiDAR data, and not yet matched against books, race records or lists — it may be well known to locals under a name we've never heard. It was cross-checked against the OS road network, surface models and map tags, but a discovery can still be an artifact of the terrain model or the map. Treat it as a well-evidenced hypothesis until someone has ridden it. If you know this road, tell us what you found — photographs, corrections and local knowledge all welcome; the map links below let you scout it first.
≈ Overhead cover (tree canopy or structures) spans 14% 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) | ≈43% | 391–393 m | under overhead cover terrain reads 60.3% at 1280–1282 m across a structure — excluded |
| 3 m (diagnostic) | ≈42% | 390–393 m | under overhead cover terrain reads 44.1% at 1280–1283 m across a structure — excluded |
| 5 m | 41% | 391–396 m | |
| 10 m | 39% | 390–400 m | |
| 20 m | ≈30.2% | 389–409 m | under overhead cover |
| 25 m | ≈28.2% | 381–406 m | under overhead cover |
| 50 m | ≈24.1% | 358–408 m | under overhead cover |
| 100 m | ≈20.5% | 345–445 m | under overhead cover |
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.
Ridden it, or know better? Submit data for this climb no account needed
© 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/england/bulk_dtm_1m/SU9510.tif"
],
"calculated_at": "2026-08-19T18:05:03+00:00",
"road_source": "OpenStreetMap (local PBF extract)",
"road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
"osm_pbf_path": "data/cache/pbf/england-2026-08-12.osm.pbf",
"osm_snapshot": "2026-08-12T20:21:46Z",
"elevation_provider": "Environment Agency",
"elevation_dataset": "EA LIDAR Composite DTM 1m (2022)",
"elevation_licence": "Open Government Licence v3 \u2014 \u00a9 Environment Agency",
"elevation_coverage_id": "13787b9a-26a4-4775-8523-806d13af58fc__Lidar_Composite_Elevation_DTM_1m",
"elevation_tile_ids": [
"SU9510.tif"
],
"climb_origin": "discovered",
"notes": "Coarse pass: max 8.8% over 200 m (Terrain 50), gain 24.6 m over 370 m way. EXTENDED by graph walk: +3 segment(s) at base, +0 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting. DEDUPE: absorbed 2 overlapping proposal(s): bignor-down-2, bignor-down-3 ADOPTED (England launch slice 2026-08-16): qualified-steep."
}