Stopping distance at 42 km/h — 20.4 m on dry asphalt
At 42 km/h you cover 11.667 metres every second. 11.7 m pass before the brakes bite, then 8.7 m of braking on dry asphalt — 20.4 m in all.
The surface decides half of it
At the same speed, ice takes six or seven times the distance of dry asphalt, simply because the grip is that much lower.
Twice the speed, four times the distance
Braking distance grows with the square of speed, because the energy of a moving car grows with the square of speed — and the brakes have to shed all of it.
The car moves before the pedal does
It takes about a second to see the danger and move your foot. At 100 km/h that second carries you 28 metres with the brakes still untouched.
Nearby speeds
How to read this
- Stopping distance = reaction distance + braking distance.
- Reaction distance is one second of travel, so it grows in step with speed.
- Braking distance is speed squared ÷ (2 × grip × 9.81).
- A heavier car brakes in the same distance — mass cancels out of the equation.
These are estimates. They assume a one-second reaction and a representative grip for each surface; real distances shift with tyres, brakes, slope and load.
Frequently asked questions
Q. What is the stopping distance at 42 km/h?
20.4 m on dry asphalt — 11.7 m of reaction plus 8.7 m of braking.
Q. How much longer is it in the rain?
25.6 m on a wet road, 39.4 m on snow and 69.5 m on ice.
Q. How many car lengths is that?
About 4.5 on dry asphalt, counting a car as 4.5 m.
Q. How far before the brakes even bite?
11.7 m. At 42 km/h you cover 11.667 m every second, and the reaction is taken as one second.