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Old 06-18-08, 12:27 AM   #1
Throwmeabone
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Was it a pinch flat or something else?

I was riding home today on the shoulder where there is some gravel and some small rocks/bits of asphalt. I was going pretty fast and keeping up with traffic. I rolled over some of the gravel when I heard and felt the back tire deflating. I stopped to repair it and found two TINY holes on the tube 3-4 millimeters apart. The holes were so small that I only found them by holding the tire up to my ear to listen for the hiss. At first I thought this it was a pinch flat, but I'm questioning that now because the holes were both on one side of the tube, not on the top and bottom as one would expect.

My tires are 700x28. The combined weight of me and the bike is about 260 pounds, so I had the tires inflated to 100 psi as per this chart I found on the forums. As a precaution, I increased the pressure in the back tire to 110 psi but kept the front at 100.

Do you think this was a pinch flat or something else? By the way the rim tape is hard plastic.
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Old 06-18-08, 04:25 AM   #2
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Two holes 3 or 4 millimeters apart sounds like a pinch flat to me.
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Old 06-18-08, 05:50 AM   #3
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Often called a "snake bite".
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Old 06-18-08, 07:54 AM   #4
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That chart recommends pressures far lower than Sheldon Brown's page and a formula posted here. For me on 32C's it is the difference of 50 vs 72 - that is a 44% increase in pressure.
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Old 06-18-08, 01:01 PM   #5
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That formula gave me just about 100 psi also, but it doesn't take the weight of the bike into account.

The reason I wasn't sure if it was a pinch flat is because the holes weren't on opposite sides of the tube. Hopefully I will have better luck with 110 psi.
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Old 06-18-08, 02:26 PM   #6
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Originally Posted by Throwmeabone View Post
That formula gave me just about 100 psi also, but it doesn't take the weight of the bike into account.

The reason I wasn't sure if it was a pinch flat is because the holes weren't on opposite sides of the tube. Hopefully I will have better luck with 110 psi.
I would expect "snake bite" pinch flats to be side by side and at a distance equal to the width of the rim.
But holes due to pinching the tube during installation could have just about any size or shape and on one side. Holes relative to rim strip problems will be on the rim side and closer to the centerline of the wheel.
I think Velox rim tape is usually the best choice for tube protection from the spoke holes.
In my opinion you should be running about 120 psi in your rear tire considering the total weight on the bike.

Al
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Old 06-18-08, 09:26 PM   #7
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I would expect "snake bite" pinch flats to be side by side and at a distance equal to the width of the rim.
But holes due to pinching the tube during installation could have just about any size or shape and on one side. Holes relative to rim strip problems will be on the rim side and closer to the centerline of the wheel.
I think Velox rim tape is usually the best choice for tube protection from the spoke holes.
In my opinion you should be running about 120 psi in your rear tire considering the total weight on the bike.

Al
How much do you think I should inflate the front tire?
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Old 06-19-08, 09:09 AM   #8
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How much do you think I should inflate the front tire?
110 psi
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Old 06-19-08, 09:29 AM   #9
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110 psi
Done. Thanks for the help everyone.
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