Rain-soaked motorway on-ramp with a worn tyre
It is 19:40 in November and raining steadily. You drive a 2016 hatchback with 128,000 km on the clock. Before leaving you checked the tyres: the front left reads 1.9 mm tread depth across the central band, the other three are at 3.5 mm. Pressures are correct. You enter a motorway on-ramp that curves left and climbs, with a 70 km/h advisory sign and a wet surface. Traffic on the motorway is dense at about 100 km/h. Your rear window is fogged at the edges and the wipers are on their second-fastest setting. You feel a slight vibration through the steering wheel above 90 km/h. A truck is approaching in the right lane as you reach the acceleration lane.
1. Should you join the motorway at the traffic speed, and how does the front-left tyre change your plan?
Read the worked answer
No, not at the traffic speed. The legal minimum tread depth in Belgium is 1.6 mm, so at 1.9 mm the tyre is legal but only just, and on standing water that is effectively no margin. A worn tyre clears far less water per second, so aquaplaning starts at a much lower speed. Combined with a left-curving ramp and heavy rain, this is a high-risk configuration.
Practical plan: keep the ramp speed low (well under the 70 km/h advisory, maybe 50-60 km/h), use gentle steering and no sudden braking, and only accelerate once you are straight in the acceleration lane. Match speed to a safe gap rather than to the fastest traffic, and if the truck is close, lift off and slot in behind it. The vibration above 90 km/h is a second warning sign (balance, bearing or deformation) and reinforces keeping speed down. Replace the front-left tyre as soon as possible, ideally before the next long wet drive.
2. What does the fogged rear window and the vibration tell you about your pre-drive checks, and what should you do before the next trip?
Read the worked answer
Both point to incomplete preparation. A fogged rear window in rain is normal physics, but it should be cleared with the demister before moving off, not while joining a motorway; visibility through the rear glass matters for lane changes and for spotting following traffic. The vibration is a mechanical symptom that a pre-drive walk-around would not necessarily reveal, but a short low-speed test would.
Before the next trip: clean the inside of the glass properly (a dirty film makes fogging worse), check the demister and rear wiper work, and have the front end checked (wheel balance, tyre condition, bearings). Also verify the spare or repair kit and the tread on all four tyres. In Belgian law a tyre below 1.6 mm is an offence and can cost you your conformity check, so treat 1.9 mm as a deadline, not a comfort.