Keeping our tyres in good nick should be an essential part of our vehicle’s safety routine checks. The first, and often overlooked, thing to look at is that our tyres have the right pressure. It is recommended to do this once a month. Each manufacturer establishes a range which is considered optimal for each tyre. If the pressure is higher or lower than that it will impact their grip, negatively diminishing their whole performance.
First we should be aware that pressure is expressed in two different figures. The first one indicates the recommended pressure for motorway driving and for vehicles carrying a heavy load. The second is for those with a normal load. Also depending on the car model the recommended pressure for the front wheels might be different than the one for the back wheels. The tyre pressure should be measured with cold tyres, or more specifically, the car should not have travelled for more than five kilometres during the two previous hours. If we have no choice but to check the pressure in the middle of a journey, when the car is still hot, we must add on 0,3 bars (1 bar = 1 kg./cm2 approximately) to the measurement.
Consequences of uneven tyre pressure
A tyre loses pressure naturally as a result of normal car use but it can also be affected by a slow puncture, a defective valve (or its plug) or a damaged metallic wheel. A deflected tyre increases fuel consumption and CO2 emissions, accelerates the wearing out of the sidewall (effectively shortening the life of the tyre) and overheats faster, increasing the risk of bursting. Moreover, in wet conditions the car will require of longer braking distances to stop and will be put at an increased risk of aquaplaning.
But an over-inflated tyre can also be problematic. It can lose shape, see its road grip diminished and lose efficiency at absorbing bumps and other surface irregularities. The tyre tread will also wear out more in the middle also shortening the useful life of the tyre.
In sum, having the wrong tyre pressure, whether this is higher or lower than recommended, increases the chances of suffering an accident as the ability to control the car is compromised or lost altogether. The car might be unresponsive to the driving wheel, particularly on the bends. This leads to what is known as oversteering or understeering, depending if the uneven pressure is located at the front or back tyres.