Tyre pressure is the measurement of the volume of air inside the tyre when it is inflated. Formerly measured in pounds per square inch (psi), it is now usually expressed in bar (1 bar = 14.503774 psi). Pressure will gradually reduce over time and therefore regular checking and topping-up is necessary to maintain the vehicle manufacturer’s recommended pressure. (See your vehicle owner’s manual). Never inflate a tyre to a greater pressure than the maximum that is indicated on the sidewall of the tyre.