What it does
Enter your speed, how quickly you react and what the road is like, and you see how far the vehicle travels before it stops. The distance has two parts: the reaction distance, covered while you notice and press the brake, and the braking distance, covered while the brakes slow you down.
Braking distance grows with the square of speed, so doubling your speed makes it four times longer. The bar diagram shows both parts in car lengths so the numbers feel real. Compare the cost of the trip with fuel cost, check your tyres with tyre pressure, or switch units with engineering unit converter.
How to use it
- Type your speed and pick km/h or mph.
- Choose the vehicle and the road. Edit the grip if you know it.
- Add a slope if the road is uphill (positive) or downhill (negative).
- Read the three distances and the bar diagram.
What each setting does
- Reaction time: seconds before the brakes go on. Tiredness, phones and alcohol make it longer.
- Road and grip (μ): dry 0.7, wet 0.4, snow 0.2, ice 0.1. Lower grip means a longer stop. You can type your own.
- Slope %: uphill helps the brakes, downhill works against them.
- Loaded truck: adds 0.5 s for the air-brake lag before the brakes bite. A two-wheeler uses the same grip, but in real life it has less margin when braking hard.
Worked example
At 100 km/h (27.8 m/s) with 1.5 s reaction on a dry road: reaction distance 41.7 m, braking distance 27.8 x 27.8 / (2 x 0.7 x 9.807) = 56.2 m, total 97.9 m, about 22 car lengths. On ice (0.1) the braking distance alone is about 393 m.
FAQs
Why does speed matter so much? Braking distance goes with speed squared. At 50 km/h it is about 14 m, at 100 km/h about 56 m.
Are these legal figures? No. They are physics estimates on a flat, clean road. Official driving manuals give their own tables.
Does ABS change this? ABS helps you steer while braking; the grip value already stands for good braking.
Not safety advice: always leave more room than the numbers show.
Where the numbers come from
- Reaction distance = speed x reaction time; braking distance = v squared / (2 x (grip + slope/100) x g) with g = 9.80665 m/s2. Grip values (dry 0.7, wet 0.4, snow 0.2, ice 0.1) are typical textbook figures, not official limits; check your own road authority's driving manual. Reaction time of 1.5 s is a common planning figure. Drawings are fibub's own.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.