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Rotor Minimum Thickness

Are you putting your customers and yourself at risk? There are still too many cars on the road with undersized rotors. In this article we highlight the importance of adhering to minimum thickness standards.RMT

Definition: Rotor Minimum Thickness (RMT) is the minimum safe working thickness of a rotor beyond which it must be replaced.

Risk: Continued operation at RMT, or machining below RMT, means that safety can no longer be guaranteed and serious accident could occur. RMT is determined by the motor vehicle manufacturer during initial vehicle design. A number of criteria are used to determine RMT. Listed below are some of these criteria.
1. Heat absorption and dissipation
A brake system takes kinetic energy and transfers it into heat energy. Friction between the brake pads and the rotor generates heat which is then dissipated by convection to the atmosphere.
As a rotor reduces in thickness, its ability to absorb and dissipate heat generated during braking is reduced. Once RMT has been reached, the rotor’s ability to absorb and dissipate heat is reduced to such an extent, that a significant reduction in braking capacity can result.
This can be evident in premature fade and excessive stopping distance.

2. Caliper piston retention
As rotor thickness and brake pad thickness reduces, the caliper piston moves further out of the caliper body. RMT is established to allow sufficient piston supports in the caliper when combined with fully worn pads. If the rotor is less than RMT, then the piston may jam in the caliper bore causing possible brake lock or drag. Brake drag will lead to excessive heat build up and possible brake fluid vaporisation.
This will lead to half system failure and excessive stopping distance.

3. Brake pad retention
Fully worn brake pads and less than specified RMT can allow, in some applications for the pad backing plate to jam between the caliper bracket and rotor. This will either cause brake drag or wheel lock up. Both concerns can result in loss of vehicle stability.
4. Brake fluid retention
It is also possible under certain conditions when brake pads are fully worn & RMT is reached, that the caliper piston will no longer hydraulically seal. This will mean a leak and hydraulic failure to half the system.