Most stop-distance calculators assume a car and dry asphalt. On a bike, the surfaces, brake types, and your reaction time all change the answer — by a factor of 3 between best-case dry disc and worst-case wet rim on a downhill. We separate reaction distance from braking distance and surface conditions from brake type so you can see what each factor is costing you.
| Speed | Reaction | Braking | Total |
|---|
At 45 km/h, one extra second of reaction adds 12.5 m of stop distance. Most people self-report reaction times around 0.7 s, but the real number for an alert cyclist is more like 1.0-1.2 s (you see, decide, take hands from hoods to drops, brake). At 1.5 s you're "distracted" — the time it takes to read a text.
Reaction distance and braking distance are roughly equal at 50 km/h on dry asphalt. They diverge badly in the wet — braking distance doubles while reaction stays the same.
Measured reaction times for "see and brake" events include seeing the hazard, deciding, and physically moving your hands. Pure "foot off gas" reaction is closer to 0.5 s. On a bike, the hands-to-lever movement adds another 0.2-0.4 s.
Wet asphalt coefficient of friction is about 50-70% of dry. On a bike, the smaller contact patch and absence of ABS means you can lock a wheel and skid easily, so experienced riders leave more margin and brake harder. The numbers here assume an experienced rider.
E-bikes are heavier and have higher average speeds, so total distance scales up sharply. The brake distance formula still applies.
Braking physics is well-understood, but real-world distances depend heavily on tire, surface and your threshold for locking a wheel. Expect ±20% under real conditions.
This calculator was built to answer a question most online versions skip or oversimplify. It runs entirely in your browser; no inputs are stored or transmitted. The math is grounded in standard cycling physics and physiology models, and is suitable for hobbyist and intermediate training use. It is not a substitute for a coach, sports scientist, or professional bike-fit service.
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Children under 13 are not the intended audience.
This calculator is provided for general informational and educational purposes only. It is not medical, mechanical, or legal advice. Predicted values depend on inputs you supply and simplified physical models; real-world outcomes vary. Use at your own risk. Brand names are descriptive only and do not imply affiliation.