MEASURING BRAKES ON THE VEHICLE
A perfect brake rotor may not look so perfect once it is mounted and a wheel is installed. A typical rotor can become "tilted" due to mis-mounting or due to dirt or burrs between the brake and hub. This "tilt" can lead to the rubbing of the brake pads on each side of the rotor. This "twice per revolution" rubbing generates two thin spots on the rotor or what is commonly referred to as "2nd order disc thickness variation" or "2nd order DTV". 2nd order DTV is one of the most common causes of brake pulsation.
In addition to "tilt" errors, the brake rotor can also become distorted due to improper torquing of the wheel. These distortions or "warping" are not necessarily felt during braking as most rotors or calipers incorporate some "floating" mechanism. In most passenger vehicles the calipers are allowed to "float" in order to follow the shape of the rotor. In high-performance or racing applications, the calipers are fixed and the rotor is allowed to float. Even though there is a floating mechanism in most braking systems, the local "high spots" of the rotor will develop more wear than the other places along the rotor. These worn areas become thinner and ultimately cause braking problems due to increased thickness variation and pulsation.
Brake pulsation is due to thickness variations, but your dial indicator won't see it. Unfortunately, dial indicators may actually show your brake surface as improving as the high spots are worn down. Even though the brakes feel worse and the performance and safety are getting worse - the dial indicator may show the brake as getting better. Micrometer measurements of thickness can help - but they don't have the resolution of BrakeView nor do they provide a visualization of the rotor's shape.
BrakeView allows you to measure the rotor on the vehicle with the wheel mounted; right where it matters. BrakeView's software incorporates a patented speed compensation algorithm ensuring the most accurate results and it can even handle your cross-drilled and slotted rotors. Custom probe holders can be built to adapt to your particular caliper - making mounting and measurement a "snap"!
"Generic" clamping probe holder concept Magnetic probe holder concept.