Disc Thickness Variations (DTV): Measuring Disc, Rotor Run-outs, Cause and Prevention

Disc Thickness Variation, DTV, brake kits, brake runouts, brake pads, brake rotors, rotors

Disc Thickness Variations (DTV): measuring disc, rotor run-outs, causes and preventions

If you are experiencing a pulsing brake pedal, you might have brake disc thickness variation (DTV). This is a small variation in the thickness of the friction surface of the rotor(s). This is usually caused by the rotors receiving uneven wear.

What is disc thickness variation?
Brake disc thickness variation means the thickest and the thinnest parts of the rotor. This causes the rotors to have an uneven wear. This is a rotor condition that one of the rotor surface is thicker than other.

How disc thickness variation occurs?

-The force of uneven clamping and rotating causes the disc thickness variation
-When the rotor was not install properly and wobble in patterns
-Not proper positioned caliper
-Irregular patterns brake friction
-Deposits, rust, and dirt

Disc thickness variation causes:

-Pedal pulsation, which occurs when the rotor rotates through the brake pads and calipers. It is more noticeable with heavy brakes
-Steering wheel oscillation
-Vibration, the thin and thick sections of the rotor slip in between brake rotors

How to measure rotor run-outs?

-Measure at least 6 arears of the rotor’s face
-Use a micrometer to measure the thickness of the rotor
-The measurements should not vary larger than .001 inch (0.025 mm)
-Start measuring a quarter from the edge of the rotor
-Measurements larger than .006 inch (0.15mm) is an indication of disc thickness variations and might need replacement

What is lateral run-outs?
Lateral run-outs (LRO) means the rotor thickness stays the same but the rotor plates are wobblily or moving up and down.

How to fix lateral run-outs?
-The rotors can be re-surface to the same as other rotor surfaces
-Shimming the rotors will change the run outs in the rotor

How to prevent Disc thickness variations?

-Install brake system properly, especially brake rotors, pads, and calipers
-Clean the wheels and rotors thoroughly
-Use a wrench to tighten the lug nuts to ensure lug nut torque
-Follow break-in procedure

*disc resurfacing may be required to correct the disc thickness variations, run-outs, and scorings.

Typical run-out value
Most of the rotors in the market today are range between 0.0005 to 0.001 inches

Vehicle Run-out value
Small Cars .01mm (0.0003 in)
Medium Cars .08mm (0.03 in)
Luxury Cars .50mm (0.019 in)

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