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Measuring Brake Disc Warpage...

3982 Views 0 Replies 1 Participant Last post by  Eclipze
[align=center]Measuring Brake Disc Warpage...[/align]

I suspected that one of the front discs might have been warped, so I setup a guage to measure it.

You can get these gauges from some bigger auto shops, like Bursons, or tool shops. They aren't too expensive, about $35 I think. <I used one from work :rolleyes: hehe...>

I made a bracket that bolted the gauge firmly to the fork leg, using an L piece of aluminium, 3mm thick, and a right angle bracket. It was certainly ridged enough for the test :dance:


Both discs didn't deviate more that 0.01mm, and was up and down while rotating, so no obvious warpage could be seen. I did the test by rolling the bike under its own weight.

Brake discs aren't always bent out of shape this way though! The disc can be egg shaped. A good hit to a kurb will do that! If you lift the wheel and spin it, watching from the front of the bike (for front wheel), you'd see it bob up and down.

The problem this causes is uneven / pulsing in the brakes. Often the brake discs wear in the center, where the brake pads bite on the surface. But not near the inner/outer circumference. The disc will remain thicker on these edges. So as the egg shaped disc rotates around, the thicker edge will touch the brake pads at certain points. Hence you get pulsing under brakes. The question is then... is the rim stuff, the disc stuffed or both!

You could probably setup the gauge to measure that as well. I had a front wheel that had been kurbed and the disc was egg shaped. Didn't really notice it until I took it to the track, and it really wasn't the best. Ended up replacing the rim and disc to get rid of the problem.
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