True That

As I described yesterday, I was out on Ride #5 when my rear brake began giving me trouble that I couldn't fix.

I ride a cyclocross bike, so the brakes are caliper brakes.  Cyclocross can be a muddy sport, and these brakes are pretty easy to clean:

Caliper brakes, rear view.

Caliper brakes, side view.

Since I've been in LA (the 5 rides I've described here, and some casual pedaling I did before I started this blog), my rear brakes have been giving me trouble.  I'll ride without a problem for miles, then suddenly (usually after a downhill section), they'll start rubbing on the edge of the wheel.  They are rubbing in the 'right' place (where they should when the brake is actually being applied), but just resting too close to the wheel.

When this happened, I'd use 2 tricks to fix the problem.  [Caution: I am a cycling newbie, not a bike mechanic.  I figured these out through trial and error.  They are certainly not the only - and may not even be the best - ways to deal with this problem.]  First, I'd make sure that the brake lines were moving freely.  Usually, this meant grabbing the triangular part (where the lines from both sides come together) and giving it a gentle wiggle:

Grab triangle, move gently left and right.

Secondly, I would adjust the relative position of the brake pads using these little tiny screws on the side of the brake:

Not the big one at the top, but the little one down at the bottom.

If you have a multi-hex-wrench tool for bicycles, there should be a wrench on there that fits.  Adjust a quarter turn, then spin the wheel to see if you've improved the situation.  Repeat as necessary.

Together, these two tricks would generally get me back on the road.  But on this most recent ride, nothing I did had any effect, except to get my hands all greasy/brake dusty.  Lovely.  Thankfully, I was only a few miles from my car, so I rode directly there, loaded up my bike, and took off for home.

I banished the bike to the corner at home, and moped for a day or two.  I was slowly realizing that this rubbing, which I'd been dealing with for weeks, wasn't really supposed to be happening.  This wasn't normal.  

Furthermore, letting the bike hang out in the corner wasn't especially productive, either.  So one evening, I put on some junky clothes and set out to investigate the situation further.  I was already suspicious that something might be wrong with the wheel: When I released the rear brake watched the wheel spin freely (bike upside down), it looked a little wobbly.  

To unclip the brake, grab the brake pads and squeeze.

The brake line on one side can be released (or will pop out on its own).

Now, turn the bike on its back and spin the wheel.
(Be sure to go in reverse if it's the rear wheel!)
Stand behind the bike, and watch the wheel.

Furthermore, when it caused a problem, the brake only rubbed for half a rotation, then didn't touch the rim for the other half.  To me, this indicated that there was something asymmetric about the motion of the wheel.  I did a little research, and realized that maybe my wheel wasn't 'true' (precisely circular and in one plane) anymore.

A bicycle wheel can become 'untrue' after a fall, after hitting a pothole, or following any other kind of insult to the wheel.  Apparently, this is pretty common in bicycles, and my bike had already tipped twice recently.  I also already had 2 symptoms of 'untrueness': The wheel looked like it was wobbling when it turned, and only one side of the brake was rubbing, and only for part of a rotation.  I performed a third test:

Be sure the wheel is properly and evenly attached to the bike.
Hold a marker firmly against a stable part of the frame,
with the tip just touching the wheel's rim.
(Here, I am resting the marker on the brake.)
Give the wheel a good spin.  Observe what happens with the marker.

In my case, I could actually feel the wheel get closer to the marker (pushing against it harder), and move further away (some spots on the wheel never touched the marker).  At this point, I was convinced: My rear wheel wasn't true.  And lacking the expertise/tools to fix it myself...I needed to find a bike shop.  

*shudder*