Vehicle care 153The legally permissible minimumtread depth (1.6 mm) has beenreached when the tread has worndown as far as one of the tread wearindicators (TWI). Their position isindicated by markings on thesidewall.If there is more wear at the front thanthe rear, swap round front wheels andrear wheels periodically. Ensure thatthe direction of rotation of the wheelsis the same as before.Tyres age, even if they are not used.We recommend tyre replacementevery 6 years.Changing tyre and wheelsizeIf tyres of a different size than thosefitted at the factory are used, it may benecessary to reprogramme thespeedometer as well as the nominaltyre pressure and make other vehiclemodifications.9 WarningUse of unsuitable tyres or wheelsmay lead to accidents and willinvalidate the vehicle typeapproval.Wheel coversWheel covers and tyres that arefactory approved for the respectivevehicle and comply with all of therelevant wheel and tyre combinationrequirements must be used.If the wheel covers and tyres used arenot factory approved, the tyres mustnot have a rim protection ridge.Wheel covers must not impair brakecooling.9 WarningUse of unsuitable tyres or wheelcovers could lead to suddenpressure loss and therebyaccidents.Tyre chainsTyre chains are only permitted on thedrive wheels.On vehicles with twin rear wheels,tyre chains are only permitted on theouter wheels.
