Braking distance calculator
Reaction distance grows with speed; braking distance grows with the square of speed. That is why the total climbs so fast.
s
Dry asphalt 0.7 to 0.9; wet 0.4 to 0.6; ice 0.1 to 0.2.
%
Total stopping distance
878.37m
- Distance covered while reacting
- 150.00
- Braking distance
- 728.37
- Time spent braking
- 14.567 s
- Deceleration
- 6.865 m/s2
- Deceleration in g
- 0.700
Show the working
- Speed = 100
- Reaction time = 1.5
- Coefficient of friction = 0.7
- Road gradient = 0
- v = 100 = 100
- Distance covered while reacting = 100 * 1.5 = 150
- Deceleration = g0 * (0.7 + 0/100) = 6.864 66
- Braking distance = 6.864 66 > 0 ? 100^2 / (2*6.864 66) : 0 = 728.369
- Total stopping distance = 150 + 728.369 = 878.369
- Time spent braking = 6.864 66 > 0 ? 100/6.864 66 : 0 = 14.5674
- Deceleration in g = 6.864 66 / g0 = 0.7
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- reaction distance = v x reaction time
- braking distance = v^2 / (2 g (mu + gradient))
- A downhill gradient is entered as a negative number and lengthens the stop.
This assumes threshold braking with no wheel lock and a constant coefficient. Real ABS stops are close to it on good surfaces.
Doubling speed roughly triples total stopping distance at normal reaction times.