BMW recommends that you replace tyres when the tread depth is down to 3mm. By this point, the tyre is 78% worn and road holding, acceleration and braking distances will already have deteriorated, especially in wet or wintry conditions. Remember to check your tyre pressure and tread depth once every fortnight, or before long journeys. If you are in any doubt as to the condition or legality of your tyres, contact your BMW Service Authorised Workshop for a free tyre check.