Question Topic: Vehicle loading
You should usually inflate your tyres to more than normal pressure when you are carrying a heavy load. The appropriate pressure will be listed in your vehicle handbook. When carrying a heavy load it can also be necessary to adjust your headlights. This is usually possible with a switch on the dashboard. Be sure to remember to reduce the pressure in your tyres once it has returned to a normal weight. Over-inflated tyres reduce the contact your tyre has with the road, reducing your grip and causing avoidable wear in the centre of your tyres.
Why do you need more than normal tyre pressure when your car is heavier?
When you drive with under-inflated tyres you increase wear to your tyres. This is because more pressure will be placed on the outer edges of your tyres. Under-inflated tyres also decrease your control of steering, make it harder to brake, and will lead to additional fuel consumption. All of this will cost you money and make you less safe on the road.
Theory Test Question
So, have you answered the theory test question: On which occasion should you inflate your tyres to more than their normal pressure? Let’s check over each of the possible answers:
When the vehicle is fitted with anti-lock brakes
Wrong! If a vehicle has been fitted with an anti-lock braking system (ABS) your tyres, this does not require you to inflate your tyres to more than normal pressure. Most cars are fitted with an ABS.
When carrying a heavy load
Correct! When you are carrying a heavy load it is usually recommended to adjust your tyre pressure to more than normal. You should check your vehicle handbook to find what the pressure should be adjusted to when carrying a heavy load.
When the tyre tread is worn below 2 mm
Wrong! When tyre tread is below 2mm it is usually recommended to change your tyres. The law requires that tyres must have at least 1.6mm of tread depth.
When the roads are slippery
Wrong! If you inflate your tyres to more than normal pressure your ability to brake will be worse. With more pressure in the tyres than normal, less of the tyre will be in contact with the road’s surface making it harder to slow down.
In section 14 of the official DVSA guide to driving book, it states:
Check your tyres’ pressures regularly – at least once a week. The vehicle handbook will show the correct pressure.
Check your tyres and adjust the pressure when they’re cold. Don’t forget the spare tyre and remember to refit the valve caps.
The handbook will also tell you if you need different pressures for different conditions.
Generally, the pressure should be higher for a heavily loaded vehicle or if you’re intending to drive at high speed for a long distance – for example, a long motorway journey.