Native tool · INT.01 Track · runs on this page
Braking Distance Estimator
Speed in, metres out — split into the part where you're still thinking and the part where physics takes over. Real friction values, honest reaction times.
Stopping distance · v1.0
v² / 2μg + reaction- Thinking distance27.8 m
- Braking distance43.7 m
- That's roughly14 car lengths
The physics, briefly
Stopping is two distances added together. First, thinking distance: speed × reaction time, covered at full speed before your foot even moves. Then braking distance: v² ÷ (2μg) — kinetic energy converted to heat, limited entirely by tire grip (μ) since modern brakes out-muscle traction on every surface.
The part that surprises people: speed enters as a square. 120 km/h doesn't need 20% more room than 100 — it needs 44% more braking distance. And surface dwarfs everything: the same 100 km/h stop that takes ~44 m of braking on dry asphalt takes ~197 m on ice. This is why "I have good brakes" is the wrong sentence; "I have good tires and I left space" is the right one.
Reference distances — 100 km/h, average reaction
| Surface | μ | Braking | Total |
|---|---|---|---|
| Dry asphalt | 0.90 | 43.7 m | 71.5 m |
| Wet asphalt | 0.60 | 65.6 m | 93.3 m |
| Gravel | 0.35 | 112.4 m | 140.2 m |
| Snow / ice | 0.20 | 196.7 m | 224.5 m |
FAQ
Kinetic energy grows with the square of speed. The brakes must convert all of it to heat, so the braking phase scales with v² — 100 to 0 takes four times the distance of 50 to 0.
Typical engineering coefficients: dry asphalt 0.90, wet 0.60, gravel 0.35, snow/ice 0.20. Real grip varies with tires, temperature and surface condition — treat results as representative, not exact.
At 100 km/h you cover 27.8 metres every second before touching the pedal. Going from alert (0.8 s) to distracted (1.5 s) adds ~19 metres — often the difference between stopping and not.