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Corner speed and lean
How far you lean in a corner at a speed, and how fast each descending style takes it.
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Corner speed and leanFondoLab
26°
lean angle
- Cautious
- 28 km/h
- Normal
- 32 km/h
- Confident
- 36 km/h
A 20 m corner at 35 km/h needs the bike leaned over 26°.
What moves it
- 5 km/h faster
- +6°
- Half the radius
- +18°
| Radius | Cautious 17° | Normal 22° | Confident 27° |
|---|---|---|---|
| 10 m | 20 | 23 | 25 |
| 15 m | 24 | 28 | 31 |
| 20 m | 28 | 32 | 36 |
| 30 m | 34 | 39 | 44 |
| 50 m | 44 | 50 | 56 |
| 100 m | 62 | 71 | 80 |
How we got this
The formula with your numbers in it, then every constant we used and where it comes from.
The working
- tan θ = v² ÷ (g × r) = 9.7² ÷ (9.81 × 20) = 0.48, so θ = 26°
- Sideways acceleration 0.48 g, which your tyres' grip must hold
The numbers and their sources
A number marked FondoLab default is our judgement, not a study's finding; we say so rather than borrow authority.
| Number | Value | Basis |
|---|---|---|
| Lean in a corner | tan(θ) = v² ÷ (g × r) | The lean that balances a corner at a speed: steeper with speed squared, gentler on a wider corner. An expert rider's measured lean followed it reasonably well. It assumes enough grip; wet roads, gravel and paint give less. [1] |
| Descending | cautious 55 km/h, 17° lean · normal 65 km/h, 22° · confident 75 km/h, 27°; braking 3 m/s² | The speed a corner allows follows from its radius and how far the rider leans: tan(lean) = v² ÷ (g × radius). We read each corner's radius from the course every 25 m and brake for it in time. The top speeds, lean angles and braking are FondoLab defaults. [1] |
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
System development with a small field test (conference paper) · One expert rider on a campus downhill with corners of 30 and 50 m radius, speed held at about 25 km/h by an automatic brake, three runs. · Read by us: Full text (open access)
Describes downhill cornering as three skills: anticipating hazards and judging the situation, controlling the bike's lean, and controlling speed.
- The theoretical lean angle for a corner follows from speed and radius: tan θ = v² / (g R).
- The expert's measured lean followed the theoretical lean reasonably well, and he started leaning about 5 m before the start of the corner.
- An earlier study by the same group found that some beginners leaned their bikes more than the expert in the same corners, which the authors link to tyre slips and falls.
Read more: Cornering: how speed, radius and lean go together
How far you must lean in a corner follows from your speed and its radius. What that means for grip, where to brake, and the line fast riders take.
On your race
Race pacing: this physics on your own course, with race-day wind and air
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