Kwik Fit has said that 69% of cars it checked had tyres under-inflated by at least 3psi (that is typically around 10%). The company reckons it adds up to an annual bill of £1bn, due to excess fuel consumption – it takes a lot more energy to make a wheel rotate if the tyre is soft, as anyone who has tried to push a car with a flat tyre will attest.
Kwik Fit also says that if your car has air conditioning fitted, you should use it outside urban areas rather than putting a window down. The extra aerodynamic drag at medium and high speeds can reduce fuel consumption by 5%, which is far more than the cost of driving the air conditioning unit.
At the same time, TyreSafe, a non-profit organisation, has said that checking tyres is especially important as we approach the Easter holidays. With families going away, having the correct air pressure is particularly critical because of the increased vehicle weight from a full car. Therefore, vehicles may need to have their tyres inflated to a higher pressure to stay safe.
One of the reasons for so many under-inflated tyres nowadays may be that you can no longer see that tyres are going soft. In the days of tall tyres with a width to height ratio of 70 or 80 (e.g. 135/80x13), a soft tyre would visibly sag. With today's stiff, low profile tyres (e.g. 205/55x16), the presssure has to be close to zero before any difference is visible. The days of kicking a tyre to tell if it is OK are long one.