Posted at: Feb. 12, 2023
If you hear a strange "shuffling" noise coming from the disc rotor area of your disc brake bicycle, it could be disc rotor distortion. This section summarizes why disc rotor distortion occurs and how to correct the distortion.
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Disc brakes on road bikes, MTBs, and other bicycles are designed to brake by tightening the rotor, which rotates around the hub, with a caliper. Disc brake installations set the position of the pads on the caliper “to match when the disc rotor rotates in a straight line, not touching from side to side.
On the other hand, if the rotor distortion occurs, the rotor will rotate swaying from side to side when viewed from above. As the rotor swings from side to side, the distance between the rotor and the caliper pad changes, causing the rotor to rub against the pad even when the brake is not closed.
If you hear a strange “shuffling” noise coming from near the rotor, it is evidence that the pads and rotor are rubbing against each other. In this case, it is safe to assume that the rotor is distorted.
Since the disc rotor is a sheet of metal, it will bend and distort if a large force is applied to it from the left or right.
Large force is a case-by-case basis, but even hitting something against the rotor when replacing a wheel or a strong impact on the rotor when falling off a car can cause the rotor to distort.
Conversely, unless a large force is applied, rotors rarely distort spontaneously.
Distorted rotors mean that the pads wear out faster because the pads and rotors are constantly rubbing against each other at regular intervals. In addition, the pads will have an unnatural hit on them, so when they are replaced with different rotors, there is a possibility that the hit will not be firm.
If the brake pads do not hit the brakes properly, the braking power will naturally be reduced. Since the ability to brake firmly is directly related to the ability to ride a bicycle safely, riding with a distorted rotor is a major problem.
Also, as explained earlier, a distorted rotor will cause abnormal noise. It is not good for your mental health to run while listening to the strange noise all the time.
It is not possible to check if a disc rotor is distorted just by a quick glance from the outside.
To check for warped rotors, you should
The following methods are the easiest to use. If the rotor rotates in a straight line, there is no problem. However, if the rotor moves left or right, there is a possibility that it is distorted.
Since the rotor is a sheet of metal, it can be corrected to some extent by applying force in the opposite direction of the distortion. Since most bicycle rotors are thin, correction can be done by an individual.
The best way to do this is to use a special tool for rotor correction. With the special tool, it is possible to bend the rotor from the root so that it can be properly corrected.
If you do not have a special tool, you can use a monkey wrench at home. However, since the correction cannot be made from the root of the rotor, it may not be possible to fully correct large distortions.
The procedure is as follows. 1.
If you do this with full force, you risk damaging the rotor, so bend it lightly with a few “kukkuks” using small force.
Repeat this several times, and when the noise stops, the correction is complete.
New disc rotors of higher grade are expensive, but middle grade or lower disc rotors are not that expensive.
If you are not able to correct the disc rotors by yourself, or if it is too much of a hassle, replacing the rotors is an option.
Disc rotors are sold at low prices at flea markets and auctions, but most of them are sold by amateurs who do not check the decrease and distortion of the rotors.
On the other hand, used bicycle stores that specialize in bicycles basically check rotors for wear and distortion (if not checked, an explanation is provided to that effect), thus preventing problems with distorted rotors.
Since rotors are part of the brake system and a safety-related part, it is best to prioritize quality over cheapness.
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