Twenty-Five Metres and a Car That Pulls Out
You are riding at 50 km/h in a built-up zone on a two-lane urban road. The surface is dry, worn asphalt; your tyres are good and the bike has ABS. A car parked 10 m before a side road on your left flashes its headlights and pulls out, stopping with its front bumper across your lane about 25 m ahead of you. Behind it there is a clear gap of roughly 3 m back to the side road, and the oncoming lane is clear for at least 40 m. Inside the next 15 m of your own lane there is a patch of loose gravel and a wet cast-iron drain cover. A car is following you at about 15 m. Your realistic reaction time is 0.75 to 1.0 seconds.
1. Calculate whether you can stop before the car, and state what the numbers mean for your decision.
Read the worked answer
Do the arithmetic, then interpret it honestly.
Convert speed: 50 km/h ÷ 3.6 = 13.9 m/s.
Reaction distance
- At 0.75 s: 13.9 × 0.75 = 10.4 m
- At 1.0 s: 13.9 × 1.0 = 13.9 m
Braking distance on dry asphalt with a realistic friction coefficient of about 0.8:
- d = v² / (2 × μ × g) = 193 / (2 × 0.8 × 9.81) = 193 / 15.7 ≈ 12.3 m
Total stopping distance
- Best case: 10.4 + 12.3 = 22.7 m
- Realistic case: 13.9 + 12.3 = 26.2 m
Against 25 m of space, this is marginal - right on the edge.
What that means
- If everything is perfect - dry surface, full attention, perfect progressive braking from the first instant - you stop just short.
- Add the gravel and drain cover at 15 m, or half a second of hesitation, and you do not.
- Therefore the correct decision is not "I can stop, so I'll coast up to it". It is: brake immediately and hard, and treat the stop as something to be achieved rather than assumed, while keeping the escape options open.
The point of the calculation is that a marginal stopping distance is, in practice, a failure. The rider who rides at 50 km/h past parked cars with side roads must already have reduced speed before the hazard appears.
2. Compare braking in a straight line with swerving, given the gravel, the drain cover and ABS.
Read the worked answer
Brake first, then decide about the swerve - in that order, not simultaneously.
Braking straight
- Uses both tyres' full contact patch for one job. With ABS you can hold firm pressure without the front locking; the system modulates faster than any hand.
- The gravel and the wet drain cover reduce available grip locally. On a μ of about 0.4, braking distance from 50 km/h alone becomes 193 / (2 × 0.4 × 9.81) ≈ 24.6 m, plus reaction - well beyond 25 m.
- So the goal is to shed speed before reaching the gravel, then cross it upright with brakes eased.
Swerving
- A swerve converts grip into lateral force and leaves less for braking. At 50 km/h into a 3 m gap, the required lean angle and steering input are substantial, and doing it on gravel or a wet iron cover is inviting a low-side.
- It is a valid option only if: the oncoming lane is genuinely clear (here it is, for about 40 m), you have already shed speed, and the surface you are swerving onto is decent.
- Brake-then-swerve is far safer than swerve-while-braking, because the suspension and tyre are settled before the lateral demand arrives.
Decision here
- Immediate progressive but firm application of both brakes, straight line - this buys maybe 10–12 m/s of speed loss before the gravel.
- Ease the front brake as the gravel and cover arrive, cross them upright.
- If the stop is still not going to happen, release and take the clear oncoming lane, aiming for the 3 m gap behind the car.
ABS note: it will not lengthen your stopping distance on gravel the way a locked wheel would, but it cannot conjure grip. Ride to the surface you can see, not the one you would like.
3. If the front wheel does step out on the gravel mid-braking, what do you do, and what must you avoid doing?
Read the worked answer
What is actually happening: the front tyre has exceeded its available grip on a loose surface and is either locking briefly or sliding sideways. It feels violent and it is usually recoverable - the mistake riders make is the reaction to the feeling, not the surface.
Do, in this order
- Ease the front brake lever smoothly - do not release it altogether and do not grab it again. A gradual release lets the tyre start rotating and regain grip without a second shock.
- Keep the bars straight and the bike upright. Any steering input while the front is sliding will convert a straight-line slide into a fall.
- Let the bike run onto better surface. Do not try to force it back onto your original line while it is still on the gravel.
- Use the rear brake lightly to stabilise if you need to keep shedding speed - but gently, because a rear wheel sliding on gravel is its own problem.
- Look where you want to go, which is the clear tarmac beyond the gravel or the gap behind the car - not at the car.
Avoid
- Grabbing the front brake again. This is the instinctive response and it is what puts the bike down.
- Standing the bike up and stamping a foot down. At 30–40 km/h your foot will not save it and the bike will run over your leg.
- Target fixation. Staring at the car's bumper guarantees you ride to it. The eyes lead the hands.
- Swerving and braking at the same time on the loose surface - you have grip for one job, not two.
Then, once stable: reassess, stop if you can do so safely, and expect the following car 15 m back to be arriving right about now - a shoulder check before you brake hard again is essential, because the hazard behind you is now as real as the one in front.