What Car? investigates: tyre safety - The financial cost
Firstly, you'll be spending more on fuel. Your car has to work harder simply to turn the wheels in a straight line when the tyres are under-inflated, and that means pumping more money into your fuel tank, and more carbon dioxide into the air.
Secondly, you'll shell out for new tyres more often. The RAC Foundation estimates that under-inflation of 20% can reduce tyre life by nearly a third.
Given that a single tyre for a popular car such as the Ford Mondeo could cost as much as £180, the extra expense could run into thousands.
Thirdly, should the police spot your under-inflated tyres, you could be hit with a £2500 fine and three penalty points - per wheel.