Alignment: Testing and Inspection
General Information On The Topic Of Tyre Wear, Wear Patterns And
Inconsistent Steering Wheel Angle
Notes on reading the DOT number
Information on runflat and wide tyres
As far as rolling comfort is concerned, driving on the RSC runflat tyres used by BMW is similar to driving on wide (17"/18"), sporty, low-cross-section tyres of normal design. As BMW has a sports orientation in the configuration of its chassis, the new tyres are very suitable for all BMW vehicles as a general principle. Of course they are also used to an increasing extent at BMW on account their other advantages (see below). Also because of the high demands for comfort - in particular in the new 5 Series models - all basic and standard tyres (16" 6-cylinder) and (225/50R17 8- cylinder) have been developed with an emergency wheel, providing particularly comfort conscious BMW 5 Series drivers with an alternative at all times. The optional accessory and special accessory tyres (in 17" to 19") have been consistently configured and developed exclusively in RSC runflat with all the other advantages of the new tyre technology (safety and convenience in the event of a breakdown, greater driving stability, shorter braking distances, absence of a spare wheel / more space in the luggage compartment, etc.).
BMW tyres are optimized in different dimensions, matching the character of each vehicle. In the development of new tyres, particular attention is paid to achieving the best possible balance of all characteristics. One possibility to influence the characteristics is the tread design. Here, the tread depth and its distribution over the running surface is used as a constructive element. High performance tyres often have a lower tread depth of only approx. 5 mm in the shoulder region and approx. 8 mm on the running surface. The consequence of this tread distribution is that different wear patterns develop on the front and rear axles while the vehicle is being driven. As a rule, the wear on the front axle is evenly distributed across the width. On the rear axle, stronger wear appears in the central area. The tyres on the rear axle usually have a shorter service life than the tyres on the front axle, as the drive power has to be transferred over these tyres.
Tyre wear
Tyres wear over the course of use. The wear depends von the driving style. Other influencing factors are road surface conditions and type of roads, the mean ambient temperature and the drive concept of the vehicle. Tyres on powerful vehicles that are frequently driven at high speed mainly wear in the centre of the tyre. The wear occurs due to the slight enlargement of the tyre diameter in the centre of the running surface, caused by high centrifugal forces.
Notes on tyre damage
The most frequent reason for all damage to tyres is driving with tyre pressure that is too low. The inflation pressure can drop slowly over time, which remains unnoticed without inflation pressure checks at regular intervals. Initially, inflation pressure that is too low leads to increased wear on the tyre shoulders. Even a drop in inflation pressure of 0.3 bar in relation to the recommended value (inflation pressure tag) can lead to greatly increased wear in this area. Furthermore, the tyre shoulders and side panels are flexed more strongly, which causes them to heat up considerably. On long journeys at high speed, the temperature can rise to such an extent that signs of disintegration become apparent and in the worst case the tyre is destroyed. This is why it is necessary to check the tyre pressure regularly (every two weeks, as recommended in the Owner's Manual) and correct it if necessary. Isolated damage to the side panels indicates impacts on a kerb. Cord breaks in the running surface area are caused by driving over sharp edged obstacles. Both are helped by inflation pressure that is too low. Isolated points with greatly reduced tread depth are usually caused by the brakes locking up with the wheels stationary.
Tyre damage patterns
A worn outer shoulder does not violate the law. However, the substructure of the tyre must not be damaged.
In some cases, saw-toothed wear can be observed on the front tyres of rear-driven vehicles. The individual cleats of the tread wear down due to the slip that occurs when the vehicle rises from the road surface as inner tensions are discharged. Saw-toothed wear can lead to increased running noise.
Different abrasion patterns occur on the front and rear axles. In the interests of safety and optimal chassis conditions, wheel exchanges from one axle to the other are not recommended.
Inconsistent steering wheel angle
The main complaint in the area of chassis adjustment is an inconsistent steering wheel angle. The problem is the driver's subjective perception of the steering-wheel position when driving straight ahead. It must be borne in mind here that the perception of the driver can deviate from the actual horizontal position of the steering wheel. This deviation mainly depends on the design and installation tolerances of the dashboard, operating levers etc.
Notes on reading the DOT number
The DOT (Department of Transportation) number indicates the date of manufacture of the tyre. The following examples explain how to read the DOT number.
DOT 016 - here, three digits without additional marking (1980s) -01 indicates the calendar week in which the tyre was manufactured. 6 indicates the year of manufacture, in this case 1986.
DOT 128< - here, three digits with arrow mark (1990s) -12 indicates the calendar week in which the tyre was manufactured. 8< indicates the year of manufacture, in this case 1998.
Tyres as of date of manufacture week 01 in the year 2000 have a four-digit DOT number. DOT 0100 (see illustration) indicates that the tyre was manufactured in the 1st calendar week of 2000.
