The Schrader valve on my 26 x 1.75 mountain bike rims keep getting cut off. Anyone know why?

Question

This happened with an old rim I had, so I replaced it and had the bike shop put on the new tire (as I thought it might be my mistake in installation). Sure enough, the NEW tube with the NEW rim failed. The valve came clear off mid-ride and was gone to the street. I can't figure it out. The tube is a Bontrager. It only happens on my front wheel.

Answer 1

Bevel the edge of the hole on the inside of the rim to remove *any* possible sharp edge. Then, make sure your rim tape completely protects the tube from the (beveled) edge. Finally, make sure the new tube is not pulled crooked through the hole. Although schrader stems aren't particularly fragile, it's possible to cut the rubber through careless use of a frame pump.

Answer 2

What will have happened is that each time you brake hard the tyre and tube slip around the rim a very tiny amount.  The valve stem is the only point that the tube is fixed to the rim.  So as you keep braking the tube is slowly stretched on the trailing side of the valve stem. Eventually it blows or just rips off. The thinner "performance" tubes rip really easy.

If you mix some flour and water into a paste and dab it between the tyre and the rim, all the way round and both sides. (inflate the tyre after and leave overnight to dry)) This will act like a retaining compound and stop the tyre slipping. Being a quite weak glue it will still allow you to get the tube out the next time you get a flat. Keeping the tyre pressure higher helps also.

Keep an eye out for bike wheels where the stem is pointing at an odd angle they are about to have the same problem. Try to tell the rider what is happening.

Sorry I didn't save you the cost of a new rim

Answer 3

could be from under inflated tires. i tell people to keep the tires inflate with in five pounds of the max pressure. the tires should have a rating on the sides.

Answer 4

This may not be the case in your situation; however, when I worked in a bike shop, what I saw most often associated with this was tires that weren't pumped up. Most people believe that bike tires are like car tires, they only need to be pumped up every 2 months...unfortunately that isn't the case. Bike tires need to be checked every time you ride. What could be happening is the tire/tube doesn't have enough pressure and the tire is shifting when you're riding. This shifting would cause the valve stem to shift also cutting the tube on either side of the stem. The thing that baffles me here is that it is normally the rear that does this. Let's see if anyone else out there in cyberworld has any other ideas.