Modern cars are fitted with a brake system using disc brakes. This system guarantees weight reduction, simpler inspection and maintenance, and excellent brake deceleration. The developers of new vehicles are paying increasing attention to safety, mileage cost and comfort. The balancing of the brakes is essential for the achievement of these objectives.
Friction between the brake pads and the brake disc causes heat and wear on both components. Optimum brake deceleration can be achieved only if both parts are completely flat and parallel. As soon as one of these components is replaced because of wear, the other must be adjusted to fit as well as possible to its new "partner".
Because of constant refinement of materials, assembly tolerances and quality awareness, even minor defects in disc brakes are noticed by the driver. Vibration in the steering wheel or brake pedal can be felt immediately and brake noise is audible. There are three directly attributable causes:
Run-out is oscillation of the brake disc. This may be caused by tolerance in the brake disc and hub or by distortion of these parts by shock loads. The oscillation of the brake disc can be felt in the steering wheel. The brake disc and the brake pads are not in line!
Disk Thickness Variation (DTV) is the difference in thickness of the disc measured at different points in the radial plane. This phenomenon is the logical consequence of differences in material structure, run out and constant changes in brake conditions such as ambient temperature, humidity and load on materials. DTV can be clearly felt in the brake pedal. Once again, brake disc nd brake pads are out of line!
Roughness of the brake disc surface leads to high or low frequency vibration of the brake components. The differences in surface structure do not conform to the manufacturer's specification and will result in excessive brake noise.
An independent Dutch magazine wrote an article about the problems of brake discs; Run-out, DTV and Roughness. In this article a Dutch car mechanic states that only by aligning the disc the problems are solved for good.