Loading a Hatchback for a Long Trip with a Damaged Tyre
Your five-year-old hatchback passed its NCT 11 months ago. You are loading it for a 200 km drive to Kerry with four adults, a full boot and a roof box. The handbook gives 2.1 bar front and rear, rising to 2.4 bar rear when fully laden, and a maximum roof load of 75 kg; the bars and box together weigh 22 kg and carry 40 kg of luggage. Checking cold pressures, you find front left 2.1, front right 1.7, rear left 2.0 and rear right 2.4 bar. The front-right tyre is a 205/55 R16 with 1.7 mm of tread at the centre and 1.4 mm at the outer edge; there is also a bulge on its inner sidewall that you noticed while crouching down. The tyre-pressure warning light is on. The spare is a 15-inch space-saver marked with a maximum of 80 km/h.
1. Which of these faults would stop you making the trip as loaded, and why?
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Ranked by seriousness:
- The sidewall bulge is decisive. A bulge means the casing is damaged. It can fail without warning, and with four adults, a roof box and sustained speeds on the way to Kerry a blowout is a real risk. That tyre must be replaced before departure - inflating it is not a repair.
- Tread. The Irish legal minimum is 1.6 mm across the central three-quarters of the tread, around the whole circumference. At 1.7 mm in the centre and 1.4 mm on the outer edge, this tyre is at or below the limit in places. Even where it is technically legal, a worn tyre with a full load will brake and clear water badly.
- Pressures. Front right is 0.4 bar under the handbook figure, and rear left is 0.4 bar under the laden figure. Under-inflation builds heat and can lead to failure at motorway speed.
A TPMS light will not detect a bulge or sidewall damage, so it is no substitute for looking. Verdict: replace the damaged tyre, set all pressures, then travel.
2. What should the correct pressures be, and when and how should you set them?
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Use the handbook figures adjusted for load: 2.1 bar front, 2.4 bar rear when fully laden. That means adding 0.4 bar to the front right and 0.4 bar to the rear left; front left and rear right are already correct.
Set them cold, before the car has been driven far, because tyre pressures rise as the tyres heat up and a hot reading will mislead you. If you must inflate when hot, add roughly 0.2 bar above the cold figure and recheck when cold. Never exceed the maximum pressure moulded on the sidewall.
Also check the space-saver. Temporary spares are usually inflated far higher than road tyres, often around 4.2 bar, and an under-inflated spare is useless when you need it. After inflating, reset the TPMS as the handbook describes - otherwise the light stays on and you have lost a useful warning. Recheck the pressures the morning after loading, since a heavy car with a roof box works its tyres harder.
3. If the front-right tyre fails and you fit the space-saver, what constraints apply for the rest of the journey?
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The car becomes a limited-speed vehicle. The space-saver is marked 80 km/h: stay at or below that, avoid hard braking, hard cornering and sustained high speed, and treat it as a way of reaching a tyre depot rather than as a way of covering 200 km. Grip and braking are reduced, and the difference in rolling radius can confuse ABS and traction control.
Combine that with the roof box. Your load, 22 kg of bars and box plus 40 kg of luggage, is 62 kg, which is inside the 75 kg roof limit. But it raises the centre of gravity and adds drag, and both matter more on three normal tyres and one space-saver, especially in wind or rain. Some space-savers also have a lower load rating than a full-size wheel, so a fully loaded car is exactly the wrong combination.
The sensible plan is to have the damaged tyre replaced before leaving, so the trip is made on four matching, correctly inflated tyres.