km/h
sAround 1 second is a common figure for an alert rider; it is often longer.
gAround 0.8–1.0 g is possible for a skilled rider on good tarmac with ABS; less in the wet.
Result
Total stopping distance77.0 m
Reaction distance27.8 m
Braking distance49.2 m
How it is calculated, with your numbers
- Speed in m/s
v = speed / 3.6100 / 3.6 = 27.78 - Reaction distance
react = v × t27.7778 × 1 = 27.8 m - Braking distance
brake = v² / (2 × a × g)27.7778² / (2 × 0.8 × g) = 49.2 m - Total stopping distance
total = v × t + v² / (2 × a × g)27.7778 × 1 + 27.7778² / (2 × 0.8 × g) = 77.0 m
Working uses the metric units the formula is written in.
- speed Speed (km/h)
- t Reaction time (s)
- a Deceleration (g)
- v Speed in m/s
- react Reaction distance
- brake Braking distance
- total Total stopping distance
What it means
Stopping takes two phases. First you travel at full speed while you react and get on the brakes. Then the bike slows at a roughly constant rate: distance is v² / (2a). Doubling speed doubles the reaction distance but quadruples the braking distance.
Assumptions and limits
- Constant deceleration from the moment braking starts; real braking ramps up over a fraction of a second.
Sources
- Gillespie, T. D., Fundamentals of Vehicle Dynamics, SAE International, 1992.