Saturday, March 22, 2008

31.8 mile FLAT FRONT TIRE!

Today when I went down to the basement to get my bike for a ride, I noticed that the front tire was flat. This was only after only 31.8 miles of trail riding. Although it is real easy to fix a flat tire, I am going to classify this as a major repair since it interrupts riding time.

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 are:
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 about 1 bubble per second coming from the tube 180 degrees 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. This was not the cause.

3.) A sharp point on the rim or a spoke poking through the rim tape punctured the tube: The rim tape was intact. At the area of the leak is also where the rim seam occurs. This is where the aluminum rim is weld to form the circle. It is too coincidental that this was the leak location. The tube leak was more on the outside diameter than the inside diameter so it does not exactly line up to the seam. Although the rim seam felt smooth, it possibly could be the cause.

4.) A tube manufacturer's defect: I cut out the section of the tube to examine the leak. The hole is so small that you cannot see it even when you stretch the rubber. There are 2 main seams in the tube but there appears to be two minor seams also. Each seam is 90 degrees apart. It looks like to me that the leak is on one of the minor seams. I believe this could be the likely cause.

To address the rim seam possible cause, I cut a piece of the old tube and glued it over the rim seam.

To address the tube manufacturer defect possible cause, I replaced the tube. The original tube was schrader valve tube and I replaced it with a presta valve tube. The schrader valve is a bigger diameter hole on the rim, therefore you need to insert a presta adapter into the hole. The presta adapter is just an aluminum sleeve.

The original tube was a Cheng Shin 700 X 52/47 tube #20097632. I googled Cheng Shin and found that they are the 12th largest rubber manufacturer in the world. They go by the name of Maxxis in the United States.

This is a presta valve.

When you put the tire back on the rim, pay attention to the rotation arrow to install the tire correctly. I then inflated the tire to 40 psi.
I will now need to buy a replacement tube. Maybe I should get 2 just in case the other tire also has a "manufacturing defect".
I will not preemptively replace the tube so I can report what happens.


Anonymous said...

a flat tire is a major repair? you could lose a lot of cred here. kama

Mike said...

I know what you are saying. As a said in my post "Although it is real easy to fix a flat tire, I am going to classify this as a major repair since it interrupts riding time."

I will classify anything that interrupts ride time as a major repair. I should also add a category for routine adjustments. Routine adjustments are like adjusting brakes for normal wear, etc.