BMW Wheel Alignment Specsby JoAnn Joubert
Wheel alignment on any BMW vehicle requires an understanding of the BMW Kinematic Diagnosis System (KDS), which is an advanced system that maintains the BMW standards of handling, speed, precision and performance. The specifications required for proper wheel alignment have much to do with the camber and caster measurements, along with the toe. By knowing these specifications for your BMW you will have a much easier time working with the KDS and aligning your tires.
First of all, you must understand the definitions of toe, camber and caster. When viewed from the top of your vehicle, the toe is merely the angle of the wheel in relation to your BMW. Most rear-in vehicles have a high "toe-in," which improves steering stability as the wheels are turning in toward each other slightly. Conversely, "toe-out" would equate to an improved turn-in while driving. In addition to knowing the definition of toe, you must also understand that there are two very valuable measurements that you must understand in order to comprehend BMW wheel alignment specifications. These are the camber and the caster.
The camber is nothing more than the inward or outward tilt of the tire, which is measured in degrees. Of course, this is also measured from the front of the vehicle. Having a negative camber means that the top of the tire leans inward. Conversely, a positive camber equates to the tire leaning out. Zero camber is the result of the tire being straight up. A positive camber results in a reduction of steering efforts and an improvement of high-speed stability in your BMW, whereas a negative camber would result in an improvement of handling and low-speed stability.
The caster is read from the side of the vehicle, being the position of the wheel in relation to the strut centerline. In order to have a positive caster, the top of the strut must be behind the wheel center. This is the situation with most vehicles, including BMW. A high caster results in improved straight-line stability. Conversely, a low caster angle results in a reduction of steering efforts and an improvement in turning.
Camber Caster Toe Specifications
For the front tires, it would be adequate to have a camber of -1.1° with a corresponding caster reading of 5.1°. The toe is 0.6 mm with a reading of 0°04'. Another range that works for the BMW is to have a -0.4° camber with a 6.1° caster. The toe should be 2.3 mm and 0°17'.
Camber Toe Specifications
For the rear tires, you want to have a -2.3° camber with a toe of 1.1 mm and 0°08'. You may also have a -1.8° camber with a toe of 2.3 mm and 0°17'.
Camber Caster Toe Thrust
The thrust is the difference between the front and rear wheel driving directions used to align all of your tires. This should be as close to zero as possible. For your BMW's front composite, you want to have a camber and caster of -0.5°, with a toe of 1.3 mm. Having a toe of 4.6 mm is also acceptable, but be sure that the camber and caster are -0.5°.
For the rear composite, you should have a camber of -0.3°. The caster measurement is irrelevant. The toe, however, should be either 2.1 mm and -0°06' or 4.7 mm and 0°06' to be within an accurate range.
In order to ensure your wheel alignment is done properly, the specifications for measuring accuracy and range are vital. Still, take note that the details of measuring accuracy are only applicable when using the precision rotating and sliding plates along with BMW quick-acting clamps for wheel alignment. Also, for these options, be aware that "VA" represents the front axle, while "HA" represents the rear axle.
So, for the total wheel toe (VA and HA), you need a measuring accuracy of ± 2' with a measuring range of ± 2°. This results in a total measuring range of ± 18°. For the single wheel toe (VA and HA), the measuring accuracy is ± 2' and the measuring range is ± 2°, with the total measuring range equaling ± 9°. For the camber (VA and HA), the measuring accuracy is ± 1' and the measuring range is ± 2° with the total measuring range being ± 10°. Wheel displacement for the front axle stands at measuring accuracy of ± 2' and a measuring range of ± 2°, with a total measuring range of ± 9°. The geometrical drive axis has a ± 2' measuring accuracy and a ± 2° measuring range. The total measuring range stands at ± 9°. For the castor, you want a measuring accuracy of ± 4' and a measuring range of ± 18°. The total measuring range of the castor is ± 22°. For the kingpin inclination, a measuring accuracy of ± 4' is required, with a ± 18° measuring range. The total measuring range is ± 22°. The toe-differential angle needs a ± 4' measuring accuracy and a ± 20° measuring range. The total measuring range is ± 20°. The maximum steering angle for the front axle should have a measuring accuracy of ± 4' and a measuring range of ± 60°, resulting in a total measuring range of ± 300°. Conversely, for the maximum steering angle of the rear axle, a measuring accuracy of ± 4' is necessary, with a ± 9° measuring range. Furthermore, the total measuring range should be ± 9°. Finally, for the castor correction range, a ± 4' measuring accuracy is required, along with a ± 7° measuring range and a total measuring range of ± 10°.
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