After changing my tires, I was experiencing a lot of brake scuffing noise. Although it was probably just a pad not seated correctly, it was possible I had bent a rotor while replacing the tire. It was easy enough to check.
To check runout, an inexpensive dial indicator and a sturdy stand is all you need. It's probably a good idea to ride the bike first, using the brakes to center the rotor. These fake floating rotors do flex a little and may not be centered if you have worked on them.
Click on image to enlarge it.
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Here I've attached the indicator to the work stand. It is better if you can attach it to the forks as they will move together with the rotor if you push the bike. This setup worked well enough, though, with a little care in rotating the wheel by hand. |
| Measurement | My Bike | Spec |
| Peak-to-peak runout, left rotor | 0.003-in | <0.012-in |
| Peak-to-Peak runout, right rotor | 0.0045-in | <0.012-in |
I measured the rotor on the inside of the pad area and the outside, with little difference. While I had the indicator out, I checked the front wheel eccentricity at the rim and bead, axial direction only.
| Measurement | My Bike | Spec |
| Peak-to-peak runout, at rim edge | 0.003-in | <0.080-in |
| Peak-to-Peak runout, at bead seating area | 0.006-in | <0.080-in |
Two things can be said here: the runout is well within spec, and the specs are quite large compared to Japanese bikes. You would likely notice something odd in the ride and breaking at less than the limit.
The rotors are also marked with a minimum thickness (presumably in case you turn them on a lathe). I measured my thickness with micrometers.
| Measurement | My Bike | Spec |
| Thickness, left rotor | 4.96 mm | >4.5 mm |
| Thickness, right rotor | 4.97 mm | >4.5 mm |
(after 17,400 mi sintered street pads)
I did not think to measure radial runout of the front wheel, but the specification is also 0.080-in.
After doing this exercise, I deglazed the discs with a light sanding with 100-grit sandpaper, and pushed back and reseated the brake pads. At the moment, the noise seems to have gone away.
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