Maintenance
Disc Rotors Warp Less Often Than People Claim
A rubbing disc brake is usually a caliper alignment or pad contamination problem, and treating every rub as a bent rotor leads riders to bend rotors that were straight.
A disc brake that rubs is commonly diagnosed as a warped rotor. Most of the time the rotor is fine and something else is producing the noise.
The clearances involved are very small
A disc brake runs with a fraction of a millimetre between each pad and the rotor. Any deviation across that gap produces contact.
This means a perfectly straight rotor will rub if the caliper sits slightly off centre. The tolerance is tight enough that assembly precision matters more than component straightness.
It also means light rubbing is common and largely harmless. A brake that rubs quietly and releases fully is performing normally.
Caliper alignment is the usual cause
The caliper is bolted to a mount through slotted holes, allowing lateral adjustment. If it is tightened in the wrong position, the rotor runs closer to one pad.
The standard procedure is to loosen the bolts, hold the brake on to let the caliper centre itself, then tighten. It resolves most rubbing in under a minute.
Frame and fork flex under load also moves the caliper relative to the rotor. A brake that rubs only when pedalling hard is showing flex rather than a fault.
Contaminated pads change the symptom
Oil, chain lubricant or brake fluid on a pad reduces friction and often produces squealing and inconsistent bite rather than steady rubbing.
Contamination soaks into the pad material and cannot be cleaned out. Riders frequently attempt to clean pads and conclude the rotor is at fault when nothing improves.
Replacing the pads and cleaning the rotor with a suitable degreaser addresses it. Handling pads and rotors with bare hands is enough to start the process.
Heat distortion is real and usually temporary
Rotors reach high temperatures under sustained braking, and thermal expansion is uneven across the disc. A rotor can rub while hot and run true once cool.
Riders descending a long hill often notice a rub develop and then disappear. This is normal behaviour rather than damage.
Permanent distortion requires either an impact or extreme heat with the wheel held stationary. Both are identifiable events rather than something that develops gradually.
Straightening a rotor is easy to overdo
A genuinely bent rotor can be trued with a dedicated tool, applying small corrections at specific points while watching the gap.
The material is thin and the corrections needed are minute. Using pliers or an adjustable spanner on a rotor that was straight is a common route to one that is not.
Establishing the cause before touching the rotor is therefore the important step. Alignment and pads account for the large majority of cases.
Questions readers ask
My steering feels notchy in the straight-ahead position. What is that?
An indented headset bearing race, usually caused by riding with a loose headset. The notch cannot be polished out, so the bearing needs replacing, and the adjustment needs correcting afterwards.
How long should bearings last?
It depends far more on water and grit than on distance. A bike with mudguards and dry storage can go years; one ridden through salted winters without guards may need attention annually.
