Alignment: Testing and Inspection
General Information On The Topic Of Tyre Wear, Wear Patterns And Inconsistent Steering Wheel Position
General information on the topic of tyre wear, wear patterns and inconsistent steering wheel position
Notes on reading the DOT number
Information on runflat and wide tyres
As far as tyre 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 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 optimally matched in different dimensions to the character of the respective vehicle. During the development of new tyres, particular emphasis is placed on the optimal balance of all these properties. One possibility for influencing the property is the profile design. In the process, the tread depth and its distribution over the tyre tread is utilised as constructive element. High-performance tyres often have a lower tread depth at the shoulder of only approx. 5 mm and, in the centre of the tyre tread, a tread depth of approx. 8 mm This tread distribution results in a different wear pattern forming on the tyres of the front and rear axles during driving. At the front axle, the wear is usually evenly distributed over the width. At the rear axle, there is, in contrast, a greater wear in the centre area. The tyres on the rear axle generally exhibit a lower service life than those on the front axle since the driving power must be transferred through them.
Tyre wear
Tyres wear out during their use. The wear depends on the driving style. Additional influencing factors include the road condition, the design and layout of the road, the average ambient temperature and the drive concept of the vehicle. Tyres of powerful vehicles that are frequently driven at higher speeds predominantly wear out in the tyre centre. The wear is caused by the slight enlargement of the tyre diameter in the middle of the tyre tread which is caused by the high centrifugal forces involved.
Notes on tyre damage
The most frequent cause of all tyre damage is driving with too low an inflation pressure. The inflation pressure can slowly drop over time which remains unnoticed without regular inflation pressure checks taken at short intervals. Too low an inflation pressure initially leads to increased wear to the tyre shoulders. Even a drop in inflation pressure by 0.3 bar compared to the recommended value (inflation pressure marking) can generate a greatly increased wear in this area. Moreover, tyre shoulder and side wall are flexed more greatly which causes them to heat up greatly. On long journeys at high speeds, the temperature can elevate to the point where signs of disintegration of the tyre can be seen and in the worst case, the tyre is completely destroyed. It is therefore necessary to check the tyre inflation pressure regularly (every two weeks as recommended in the handbook) and correct it where necessary. Individual signs of damage to the sidewall can be traced back to a sharp impact to a kerb. Cord breaks in the running surface area are caused by driving over sharp-edged obstacles. Both are made worse by having too low a tyre inflation pressure. Individual locations with strongly worn tread depth can usually be traced back to a heavy braking or panic stop with locked wheels.
Tyre damage patterns
At the front tyres of rear-drive vehicles, a saw-tooth-shaped wear can be partially seen. The individual blocks wear due to the slip which occurs when lifting up from the road surface due to the unloading of the inner tension. Saw-tooth-shaped wear can have an increased running noise as a result.
Different tread wear patterns form on the tyres on the front and rear axles. In the interest of safety and optimal chassis conditions, an axle-wise wheel exchange is not to be recommended.
Steering wheel inclination
The main complaint in chassis adjustments is the steering wheel position. The difficulty is the driver's subjective perception of the steering wheel position when driving straight ahead. Observe here that the driver's perception of the actual horizontal position of the steering wheel can deviate. This deviation is mainly dependent on the design and installation tolerances of the dashboard, operating levers, etc.
Notes on reading the DOT number
The DOT number (Department of Transportation number) specifies the production date of the tyre. The following examples explain how to read the DOT number.
DOT number 016 - here, three digit without additional marking (the 1980s) -01 specifies the calendar week in which the tyre was manufactured. 6 specifies the year of manufacture, in this case 1986.
DOT number 128< - here, three digit with arrow marking (the 1990s) -12 specifies the calendar week in which the tyre was manufactured. 8 < specifies the year of manufacture, in this case 1998.
Tyres after calendar week 01 in the year 2000 have a four-digit DOT number. DOT number 0100 (see graphic) specifies that the tyres were manufactured in the 1st calendar week of 2000.
