How to Test Rotor Thickness

January 27, 2012

When doing brake repair, rotor thickness is an important aspect to check. A Brake rotor must have enough rotor material to absorb and dissipate heat as well as to maintain its structural integrity, and rotors that have a thickness below minimum specifications are at higher risk for fade and cracking. Most rotors have a minimum thickness noted either on the casting of the rotor or in the factory service manual, so its important to accurately check actual thickness to ensure it is above these specifications.

When to Check

Thickness should be checked whenever brake pads are replaced, and before any resurfacing work is done. This is to ensure that the rotors have sufficient material to be put back into service. It is a good practice to do this every time the brake pads are replaced, regardless of the interval between changes. It only takes about 5 minutes or less and is a good safety measure to be in the habit of.

How to Check

Most factory service manuals are very specific about testing procedures. Using a micrometer, rotor thickness should be measured in eight to ten places, approximately 45’ apart and 10mm from the edge of the rotor. These readings should all be above the minimum specifications for thickness, and should vary by no more than the maximum brake parallelism values listed in the manual. This will help ensure smooth and consistent braking performance.

Making sure your brake rotor thickness is above the minimum listed values found either on the casting or in your car’s service or owner’s manual is an important step in brake repair. Proper measurement only takes about 5 minutes, and is a great safety buffer to ensure your braking system works exactly as intended.

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