Wet Elevated Road, Worn Rear Tyre and a Pulling-Out Bus
At 17:20 on a July afternoon you are riding a 250 cc motorcycle with ABS along a two-lane elevated urban road posted at 50 km/h. Rain has been falling for 40 minutes and there is standing water in the wheel tracks. Your rear tyre measures 1.5 mm at the centre groove, the wear indicator is almost flush, and the front tyre was replaced two weeks ago. You wear a one-piece rain suit, but the loose over-trousers flap against the footpegs above 35 km/h. A city bus is stopped 80 m ahead in the right-hand lane with its hazard lights on and its left indicator flashing. Between you and the bus are two steel expansion joints, each about 20 cm wide, running diagonally across your path, and a crosswalk whose paint is worn smooth. Visibility is about 150 m; behind you a taxi has been tailgating at 15 m since the last ramp. Your destination is 6 km further and you are already 10 minutes late for a family dinner.
1. List the hazards in the next 100 m in the order you must deal with them, and describe exactly what you do with the controls at each one.
Read the worked answer
Order: expansion joints → the bus → the taxi behind.
1. Expansion joints (arrive in about 5 s). At 50 km/h you cover 14 m per second. Wet steel has far less grip than asphalt, and with 1.5 mm of rear tread almost no water is being cleared, so the risk of a slide is real. Brake in a straight line before the joint down to about 30 km/h, release the brakes, cross upright with a steady throttle and no steering input. Never brake or lean on the steel.
2. The bus. Treat the left indicator as a promise to pull out, and assume passengers will step out from in front of it. Reduce speed until you can stop within the distance you can actually see. Do not overtake on the left into an oncoming lane; wait until you can see past the bus and confirm no pedestrian is crossing.
3. The taxi at 15 m. Do not brake-check it. Instead open a larger gap to the bus (3–4 s) so all your braking is gentle and predictable, and show the brake light early with a light tap before you actually slow.
Reduce your whole-ride speed by 10–20 km/h: the worn rear tyre lowers your cornering and braking margin for the entire 6 km.
2. You are already late. Explain how that fact should, and should not, change the plan above.
Read the worked answer
Lateness changes nothing about the road and everything about your temptation. The water, the steel, the worn tyre and the bus are identical whether you arrive at 17:40 or 18:00. What lateness does is push you toward exactly the behaviours that would convert a manageable ride into a crash: filtering past the bus, using the crosswalk paint as a passing lane, riding above 50 km/h, or skipping the speed reduction.
The correct move is to separate the two problems. Solve the schedule problem with a phone call or by accepting a late arrival - say to yourself plainly: “I will be 15 minutes late and that is the cost.” Solve the riding problem with the plan in the previous answer.
A useful test: if the only reason for a manoeuvre is the clock, it is not a riding decision. Ten minutes of embarrassment is cheaper than a slide on wet steel.
3. Your bike has ABS. Explain what it will and will not do for you on the steel joints and the worn crosswalk paint, and what that means for your braking points.
Read the worked answer
ABS stops the wheels locking, so it prevents the classic low-side from a grabbed front brake and lets you brake hard on uniform wet asphalt with far less skill. It does not create grip. On wet steel or polished thermoplastic paint the coefficient of friction is so low that the wheel can still slide, or the ABS can release and re-apply so rapidly that the bike barely slows - you simply travel further while the lever pulses.
Practical consequences:
- Finish your braking before the joint or the paint, not on it. ABS is a safety net for a mistake, not a licence to brake late.
- On a diagonal joint the two wheels cross at different moments; a braking force applied as the front wheel is on the steel can still produce a momentary washout.
- The worn rear tyre means the rear ABS will intervene early and often, so your overall stopping distance is longer than the bike's brochure figure.
- Keep the bike upright and the throttle steady across both surfaces, then resume braking afterwards.