What It Really Takes to Stop at 25 km/h
The motor on a legal eBike cuts out at 25 km/h. That sounds modest, and the physics behind it work differently from a pushbike. The numbers below are the ones worth knowing before you share a path with anyone.
An impact at 25 km/h carries nearly 3x the energy of one at 15 km/h, the speed of a typical pushbike. That energy has to go somewhere, which is why braking and following distance are skills worth practising.
Why speed counts for more than it looks
Energy doesn't rise in a straight line with speed. It follows the square of your speed, so doubling your speed quadruples the energy. Going from 15 km/h to 25 km/h increases your crash energy by 2.77 times:
crash energy
crash energy
crash energy
crash energy
Put another way: an impact at 25 km/h matches a fall of 2.4 metres onto a hard surface, roughly off the roof of a car. At 15 km/h it is closer to stepping off a kitchen bench (0.9 metres). Both hurt, but they are not the same injury.
Note: these figures assume a 100 kg total weight (75 kg rider + 25 kg eBike), which is typical. Heavier cargo or a heavier bike increases the energy further.
Real stopping distances
These figures include 0.8 seconds of reaction time before braking begins β the average for an alert adult. If you're tired, distracted, or riding at night, reaction time is longer.
| Speed | Dry road | Wet road | That's roughly⦠|
|---|---|---|---|
| 10 km/h | 2.8 m | 3.3 m | about the width of a car |
| 15 km/h | 4.6 m | 5.9 m | about the length of a car |
| 20 km/h | 6.7 m | 8.9 m | about a car and a half |
| 25 km/h | 9.1 m | 12.6 m | about the length of a bus |
You need 12.6 metres to stop in an emergency, which is longer than a bus. If something appears 8 metres ahead, no amount of braking skill closes that gap. This is why riders ease off on wet roads advice.
How far you travel before braking even starts
The stopping distances above include reaction time. But it's worth seeing how much ground you cover in that 0.8 seconds before your hands even reach the brakes:
- At 10 km/h β you travel 2.2 metres before braking starts
- At 15 km/h β you travel 3.3 metres before braking starts
- At 20 km/h β you travel 4.4 metres before braking starts
- At 25 km/h β you travel 5.6 metres before braking starts
That 5.6 metres is more than the width of two lanes of traffic. It assumes you were alert and looking directly at the hazard when it appeared. If you were glancing at your phone, checking a mirror, or looking sideways, add another metre or more.
Why an eBike hides its own speed
On a pushbike, reaching 25 km/h on flat ground takes effort. Your legs and your breathing both tell you the same thing: you are going fast.
On an eBike, 25 km/h is the default. You reach it without effort, and you maintain it without noticing. There's no physical cue that you're at a speed where stopping will take the length of a bus.
This is why new eBike riders consistently overestimate their reaction time and underestimate how long they need to stop. The bike's physics changed; their intuition didn't. Peer-reviewed research on novice e-bike riders confirms this gap between perceived and actual stopping capability (see sources below).
What to do about it
The speed limit tells you the legal maximum. Your stopping distance tells you the safe maximum for the conditions. On a wet night, 25 km/h may not be safe even if it's legal.
Every kilogram of cargo or passenger weight extends your stopping distance. A cargo eBike with 25 kg of groceries at 25 km/h needs significantly more than 12 metres on a wet road.
Most riders have never done a full-force emergency stop on their eBike. Find a quiet car park, get to 20 km/h, and practise until stopping hard is automatic β not something you're working out mid-emergency.
At 25 km/h, you cover 7 metres every second. If you're scanning 5 metres ahead, you have less than a second to react to anything. Train yourself to scan 20β30 metres ahead at all times.
By the time a hazard is visible at close range, your reaction time has already consumed most of your safety margin. Slow down before blind corners, intersections, and crossings β not when you see someone.
Ready to learn the full picture?
The eBikeSafe course covers speed management, stopping distances, road rules, night riding, battery safety, and everything else that separates a safe eBike rider from a statistic. Complete it in about 1β2 hours.
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Sources and methodology
Stopping distance calculations: Standard kinematic formula d = vΒ²/(2ΞΌg) + vΓt, where ΞΌ (friction coefficient) = 0.7 dry / 0.35 wet, t (reaction time) = 0.8 s, total system mass = 100 kg (75 kg rider, 25 kg eBike). Dry friction coefficient consistent with MDPI experimental eBike braking study (2024).
Kinetic energy: KE = Β½mvΒ². Fall height equivalence: h = KE/(mg), i.e. the height from which a free-fall would deliver the same impact energy.
Reaction time: 0.8 seconds is the commonly cited average for an alert adult; impairment (fatigue, alcohol, distraction) typically adds 0.3β0.8 seconds. Source: Austroads Road Design Guidelines.
Hazard perception gap in new eBike riders: ScienceDirect β Young novice e-bike riders and hazard perception (2020).
TBI rates in young eBike riders: University of Melbourne / The Conversation, 2025 β young eBike riders aged 10β25 suffer traumatic brain injuries at approximately twice the rate of conventional cyclists.