Friday, September 29, 2006

Stumped by the Lump

I was getting a thump-thump from the back wheel of my Saluki that I only noticed coasting down smooth asphalt. It wasn’t enough to bug me most of the time, and never when I was pedaling, but it was sufficient to mess up the bike’s feng-shui, to put in the back of my mind a vague annoyance that drew me slightly away from wanting to ride it and which also made me feel, after an hour or so in the saddle, as if I had a slight flutter of the heart.

I thought at first that the bead of the tire wasn’t set sufficiently in the rim—I’ve had occasions where the inner tube begins bulging out the side and makes for a very bumpy ride—but eyeballing it, I couldn’t see anything.

Just to be sure, though, I tried deflating the tire and pumping it back up very slowly, making sure the bead didn’t shift at any point. But I still got the thump-thump when I road.

Spinning the wheel, you could see a place where the tire rose up a little; this led me to believe that maybe the rim was out of round.

I removed the wheel, took off the tire and tube, and put the rim in my truing stand. It looked like it was just a tiny little bit out of round, maybe two or three millimeters at most. Both Alex at 20/20 and Brian Parker at Ti Cycles said they thought that wasn’t enough to make a difference; it was probably something with the tire.

I tried swapping the front tire with the rear, but I still saw the lump. I installed another brand of tire; the lump was still there.

Finally, I took the wheel over to 20/20 and had Alex adjust the roundness of the rim—a few millimeters was all, but guess what: the reinstalled tire rolls lumplessly.

My rim had a pea; I guess I’m a princess.


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