Low tyre pressure increases vehicle drag and fuel consumption. Correctly inflated tyres improve mileage by up to 3.3%, and are safer and last longer.
Ask your vehicle manufacturer for the recommended pressure or look it up in the owner's manual; in some cars it's shown inside the driver's door or in the cubby-hole. Don’t go according to the maximum pressure printed on the tyre.
Tyres lose pressure over time and at lower temperatures. Check your tyres at least monthly or whenever they look a bit flat; in the morning, before driving friction has heated the tyres and increased pressure, is a good time.
Another advantage of checking the pressure frequently is that slow leaks can be found and repaired before they cause permanent damage to the tyre.
Don't over-inflate your tyres either -- that's also not good for their longevity, and increases the risk of blow-outs.
(Olivia Rose-Innes, EnviroHealth Editor, Health24, November 2011)