Archive for February 2010

Flat Tire Fun

Introduction

As I was about to leave for work last Wednesday I noticed that the front tire of my bike was flat. “No problem”, I thought, “just a quick fix.”

This was only the second flat I have had since getting my bike, so doing this simple task takes a little longer than it should. I was “happy” to have the opportunity to rehearse the motions at home before having to do it somewhere else.

My first flat happened within a day or two of getting the bike. The cause for both flats was that the rim tape was in the wrong position. For those who do not know what I am talking about, a quick explanation follows.

Wheels

A bike’s wheel consists of a hub (the thing about which the wheel rotates), the spokes, the rim, and nipples that connect the spokes to the rim. The nipples drop in through holes in the outside of the rim (the outside being the part where the tire and tube go). These holes are drilled through the rim and have relatively sharp edges; sharp enough, at least, to wear a hole through the tube. To keep the tube from deflating due to contact with the holes, some sort of strip is placed along the trough of the rim.

This strip — rim tape — had moved out of place for both of my flats.

My rim tape is a a sort of plastic that does not seem ideal. It is not glued down everywhere. Tension is supposed to keep the unsecured portions in place, but that is where the failures keep occurring. I am going to investigate this a little more and possibly replace the rim tape with a more cloth-like tape.

Extra Trouble

Since I was in a hurry, I swapped in my spare tube with the intention of patching the other tube at work. When I got my tire back on, though, I was having trouble with one of the brake pads always contacting the disc (I have disc brakes on my bike). Before this episode I was not too mechanically familiar with the brakes.

Prior to exhausting all ideas, I looked down through the gap between the pads and the disc and noticed a piece of metal that looked entirely out of place. This gave me cause open the brake assembly and investigate, which was something I would have been doing sooner or later with or without cause. Of course, disassembling something unfamiliar always carries the exhilarating possibility of not knowing how to reassemble it.

I found two bolts that appeared to hold the thing together and was amazed at how much they had been tightened. (Note to self: check if the bolts were tightened to some specified torque and handle as appropriate. The idea of the brake assembly coming apart during a ride is unappealing.)

When I finally got the two bolts out, half of the brake came off (as expected) and then popped into three pieces. Not too bad, but you never know what you are going to get. The pieces’ purposes were pretty straightforward: the external housing, the brake pad, and a semi-springy metal piece that serves a role of limiting the motion of the brake pads. The out-of-place piece of metal that I referred to above was the semi-springy piece. The issue was that one of the “arms” had been bent and was between the brake pad and the disc. I am not sure if it was there before the tire was removed and replaced, but it seems fairly certain that the squeeky noise coming from the brake recently was related to this.

Using pliers, I simply bent the part back into its intended shape. Hopefully that will be the end of that. If that part was between the disc and brake pad for a while, I suspect the pad may have worn unevenly. I did not think to investigate this before reassembling the thing, but I will check it out next time the brake is disassembled.

I wish I had taken pictures of all of this to make it more compelling, but I was in a hurry.

Next Time

Overall, I enjoy this sort of thing. I will, however, be making changes to make the work environment more efficient.

Having a repair stand will make doing this stuff easier and more fun in the future. More space would be nice too. Also, a separate T25 star-shaped wrench would be handy. I have this wrench on my multi-tool, but it was not convenient using it through the spokes to adjust the position of the interior brake pad.

SIAM PP10

For all of you out there who are wondering where I will be from February 24, 2010 through February 26, 2010, I have your answer: I will be at the SIAM Conference on Parallel Processing for Scientific Computing (PP10). The conference is being held in Seattle, so really, I will be pretty much where I would have been anyway.

Let me know if you want to meet there.