Gears & Gadgets: The Most Annoying Sound, Part 2: Rim Brakes
by David Cohen, Maryland National Capital Park Police Reserve Unit
In the last G&G column, I detailed how to fix a rubbing disc brake. Fixing a rubbing rim brake is no more difficult, although the process is a bit different.
Rim brakes and mechanical disc brakes are similar in that they both use a cable actuated by the brake lever to engage and release the brake. Some minor rim brake rubs can be solved simply by using the adjusters on the brake levers. On road bikes with drop bars, the adjusters are often located on the brake unit itself. Turning the adjusters counter-clockwise will allow for more slack in the cable, which, in turn, will cause the brake shoes to back off. The object is to not back the adjusters off so much that the brake levers have less than an inch of space between the lever and the handlebar when fully engaged. That is the bare minimum. I prefer a quicker engagement of the brakes, so I would set mine so there is more space when the brakes are fully engaged – usually between 1 ½ to 2 inches, depending on the bike.
Before making adjustments, conduct a quick check of the rim surfaces and braking surfaces. Rim brakes by their nature are more susceptible to picking up dirt, grime and other debris than their disc brake counterparts. They also leave a buildup of brake material on the rims themselves. A quick wipe around with a cloth or paper towel is usually sufficient, but cleaning the rim with rubbing alcohol should be a monthly task. To check the braking surfaces, release them as if you were changing the tire and for any extraneous debris on the brake shoes. Usually a check with your hand is sufficient.
If you’ve gone through these steps and your brakes are still rubbing, odds are the rim is out of true. Most of us don’t carry a wheel truing stand with us, so doing a full true of the wheel really isn’t practical, but you can use your spoke wrench to get the rim to clear the brake shoe.
With the wheel in the air, give it a spin. Stop the wheel when it gets to the rub. The rubbing area should be in the 12 o’clock to 1 o’clock position, or fairly close to it. From the top, find the spoke that is closest to the rub.
The corrective action needed depends on which of the brake shoes are rubbing.
Looking down at the top of the tire with the rub at the 12 o’clock or 1 o’clock position:
Left Shoe Rubbing: Turn the left-side spoke counter-clockwise; turn right-side spoke clockwise.
Right Shoe Rubbing: Turn the left-side spoke clockwise; turn the right side spoke counter-clockwise.
This may seem counter-intuitive, but the spokes are reverse-thread. Always adjust spokes in pairs or in threes, and only make adjustments in quarter-turn increments.
If the rubbing is prolonged or the level of distortion in the true can’t be resolved after more than two full turns of the spoke wrench, then the wheel has other issues and should be looked at by an expert.
Hopefully this little tidbit will ensure long miles of quiet riding.
Next G&G we’ll discuss daytime running lights (DRLs) for bicycles.
About the author: David Cohen is a 12 year volunteer with the Maryland-National Capital Park Police. When he isn’t riding or tinkering with bicycles, David can be found tinkering with vintage cars or World War II airplanes. An avid historian, David enjoys researching and writing as well. He can be reached at onyxsax@aol.com.
Photos courtesy David Cohen.