With the DVSA releasing the latest vehicle enforcement data at the end of March the figures showed the surprising reason most drivers fail enforcement checks at the roadside is because of the condition of their tyres. According to the law the tread depth of a tyre must be a minimum of 1.6mm across the main three quarters of the tyre. If part or all of this area is below 1.6mm the tyre would be classed as illegal. Although this is the legal limit it s recommended that you should change your tyres when the tread depth reaches 3mm. This ensures your grip is at optimum levels which is particularly important in winter when the weather conditions cause the roads to be more slippery. There are a few ways to check your tread depth: Look out for tread wear indicators built into the main grooves of the tyre - if the tread is level with the top of the indicator they need to be replaced. You can also use a calibrated tyre gauge which will show you how close you are to reaching the limit. If you don t have either of the above you can do the 20p test. Place a 20p coin into the groove of your tyre - if the outer rim is obscured your tyre is above the legal limit. Tyre Pressure Ideally you need to check your tyre pressure every 1-2 months. You can find your car s recommended pressure in the owner s manual and there is often a sticker on your car door too. Plus with fuel prices skyrocketing it s even more important to keep an eye on your tyre pressure - as underinflated tyres can minimise fuel economy leading to you using more fuel unnecessarily. If you re unsure how to check your tyre pressure you need to use a pressure gauge when your tyres are cool. This will take a reading that will tell you if your tyre is under or over inflated. If it s over inflated you just need to let some air out by unscrewing the cap. If it s underinflated you ll need to use the machine at your local petrol station to put some air in. Tyres will always wear down over time but there are a few factors that contribute to wear: Avoid aggressive cornering and braking. Frequent high speed driving increases temperature and wear so always stick to the legal speed limit. Excess load increases wear so if you re frequently carrying heavy loads expect to see your tyres wear down more quickly. Check your alignment - if it s wrong or your suspension shock absorbers are worn this can cause your tyres to wear. If you are driving with unroadworthy tyres you can be stopped by the police and fined up to £ 2 500 per tyre. This means that if all of your tyres are below the legal tread depth you ll be faced with a fine of up to £ 10 000.