Sunday, October 5, 2008


This is my third flat tire, the first on the rear. It is way too many flat tires. To put it in perspective, I have over 2100 miles on my Raleigh Grand Prix road bike and have not had a flat.

When you fix a flat you need to determine what caused the flat or it will just happen again. Also I usually just replace the tube rather than do a repair since tubes are inexpensive ($5).I carefully removed the tube from the tire then investigated the possible causes. Here are my findings :

1.) Leaking valve : with some pressure in the tube I placed the tube in a bucket of water. No bubbles were coming from the valve. This was not the cause. There was several bubbles per seconds coming from the tube just a few inches from the valve stem location.

2.) An external object punctured the tire and tube: At the location of the leak there were no objects on or in the tire. I also checked the entire inner and outer surface of the tire, there were no objects. The defect was a very small "pin prick". I guess if there were a small speck of something it could eventually wear a hole in the tube. The defect was on the outer surface adjacent to the tread This is a possible cause.

3.) A sharp point on the rim or a spoke poking through the rim tape punctured the tube: The rim tape was intact. There were no sharp points on the rim. This was not the cause.

4.) A tube manufacturer's defect: The defect was not on the seam. It was a very small "pin prick". This could be the cause but it seems unlikely for a manufacturing defect to develop after 8 months but maybe so. The tube was a Cheng Shin 700 x 52/47 mm tube made in Taiwan with serial number 19097734. It also says "thin" on it. Perhaps these were put in to minimize weight. I replaced it with a CST 29 x 2.1- 2.55 tube that I bought a PricePoint. It is made in China with number 03127111 on it.

Because this is my third flat in under 300 miles, I will start buying better quality tubes. I will do some research a report out on my findings.

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