Tyre tread depthTyres with a tread depth less than the legal requirement of 1.6mm are one of the most common tire-related mistakes made by drivers. A tread depth of less than 1.6mm decreases the tyre's grip on the road, increasing the risk of accidents. A simple way to check the tread depth is with a 20p coin. A pressure gauge attached to the valve will display the tyre's pressure, allowing the driver to determine whether inflation is required. "Motorists can be fined up to £2,500 per illegal tyre, so for motorists taking a chance with four illegal tyres, they could face a fine of up to £10,000.