The brake track on the rim of my road bike is a little worn, and a rim shoulder has formed. I've heard that the rims of mountain bikes can burst, so I'm worried. Is the ledge normal or can the rim also suddenly fail on a road bike? How can I tell if the rim is still in good condition?
Matthias Kretzschmar, Vaihingen/Enz
Braking not only wears the rubber, but also the rim - hardly at all in the dry, but a lot in the rain. Dirt particles in the water rub against the rim, recognisable by the grey veil of abrasion that covers the rim and brakes. Heavy wear is caused by stones that become lodged in the brake pad. They tear small aluminium shavings from the rim flank, which also settle in the pad and remove more and more aluminium. Loud scraping noises when braking indicate this. If the foreign bodies do not come out of the brake pad even after repeated braking, you will have to remove the wheel in question and free the brake pads from the troublemakers. It is best to include this check in your regular maintenance work. The condition of the rim can be checked with special measuring devices, such as the rim caliper from Cutting Crew, phone 06172/928681, www.cutting-crew.de check.
Test results indicate that rims with a wall thickness of one millimetre or less can no longer reliably withstand tyre pressure. Many new rim models therefore have wear indicators in the form of circumferential grooves or cut-outs. Depending on the design, these become visible or disappear when the rim is worn.
