Learn · Cornering
Cornering: how speed, radius and lean go together
The short answer: the lean a corner needs follows from your speed and the corner’s radius, and so does the grip it asks of your tyres. Grip grows with the square of your speed: 10% faster asks 21% more. So do your braking before the corner, upright, and spend the grip on turning.
Speed and radius set the lean
To go round a corner, the bike and you lean until gravity balances the pull outwards. The lean angle θ follows from your speed v and the corner’s radius R: tan θ = v² / (g R), with g = 9.81 m/s² 1.
Some examples, worked out from that formula:
| Speed | Radius | Lean |
|---|---|---|
| 25 km/h | 50 m | 6° |
| 25 km/h | 30 m | 9° |
| 40 km/h | 30 m | 23° |
| 40 km/h | 20 m | 32° |
| 30 km/h | 10 m (hairpin) | 35° |
When a rider’s actual lean was measured on a downhill at 25 km/h, it followed this theoretical lean reasonably well 1.
Lean is grip you are using
The same number, tan θ, is the share of your weight the tyres must hold sideways. At 40 km/h in a 30 m corner that is 0.42; at 44 km/h, 10% faster, it is 0.51, 21% more. Grip runs out much faster than speed rises, and on a wet or dirty road there is less of it.
Leaning more than the corner needs does not help. A Japanese group found that some beginners leaned their bikes further than an expert in the same corners, which the authors link to sliding tyres and falls 1.
Brake before, not in, the corner
The tyre has one budget of grip, for braking and turning together. Brake hard while leaned over and you take grip away from turning, and the bike also wants to stand up and run wide. Do the braking upright, on the straight before the corner, then let off and turn.
Late braking is where good riders gain time. Eight World Tour riders were measured on a closed descent: the ones fastest through the tightest hairpin braked 10–20 m later than the others, and the slowest braked harder and earlier 2. Later does not mean later than you can stop: it means braking hard once, at the right point, instead of dragging the brakes into the corner.
The line
Fast riders use the whole lane. Of two riders who entered and left the same hairpin at the same place, the faster one steered closer to the inside; the slower took a consistently wider line 2. A wide entry, a late apex on the inside, and a wide exit make the corner’s radius as large as your lane allows, and a larger radius means less lean at the same speed. On open roads your lane is your lane: never cut into oncoming traffic for a line.
In the same tests, the expert started leaning about 5 m before the corner began 1. Look through the corner to where you want to go, not at the edge of the road.
The honest limit
There is little research on cycling corners. The Delft researchers called it close to non-existent in 2018 2, and the studies above are small: one expert in one, eight professionals in the other. The physics is certain; the advice on technique is the best evidence there is, not settled science.
For descents, where most of the hard corners are, see Descending.
References
- Sakai D, Uchida N, Enomoto S, Iwata S, Kawakami Y, Wesugi S (2020). Improving Road Bike Leaning Skills on Downhill Corners (Developing a System for Detecting Curvature Change Points and the Angle of a Road Bike while Riding). Proceedings 49(1):153 (13th Conference of the International Sports Engineering Association). doi:10.3390/proceedings2020049153
- Reijne MM, Bregman DJJ, Schwab AL (2018). Measuring and Comparing Descend in Elite Race Cycling with a Perspective on Real-Time Feedback for Improving Individual Performance. Proceedings 2(6):262 (12th Conference of the International Sports Engineering Association). doi:10.3390/proceedings2060262