Bicycle Mechanics - Tire/tube question
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06-12-02, 07:55 PM
Trying to reach a conclusion on my blowout.
The tire is a 700c x35. The tube in it was 28x1. What I'm wondering is if the tube being so big blew the tire off of the rim. That's exactly what I think happened. I just aired the tire up to 80psi. (tire is 85 max.) Then I took off and it blew. Tire is fine. Tire was also over the edge of the rim after it blew. The split in the tube was 15" long. Am I right? What do you think? I'm going to check the rear tomorrow and see what tube is in it.
Continental marks their 700 tubes as 28". A !" tube is actually 22mm. I don't think it's a question of the tube being too big, but I really don't have any other ideas either.
Whenever this has happened to me, it was because I didn't have the tire seated properly on the rim. But, from what you have said, you've eliminated that possibility.
Let's hope there are some wiser members who will comment.
Today's Contis require a hook-bead rim. If the inside sidewalls of your rim are smooth, the tyres will tend to blow off the rim.
06-12-02, 09:59 PM
This was a Kenda Kwik cyclocross tire if that helps any.
Using a too-small tube is a common practice with many slip-shod bike mechanics. This way, they only need to keep a few sizes on hand, and the skinny tube is easier to mount than a larger one is.
A 1" tube is made for a 25mm (roughly) tyre, wheras your tyre was about 35mm. That means the tube was stretched preety d@mn thin at full inflation. You may also have a slighly rough inner edge on your rim. This might not be a problem when using a proper sized tube, but when your tube is already stretched out like a balloon, well, it's gonna blow to kingdom come!
Another problem with using a too-small tube-when you get a puncture, then patch the puncture hole, your patch will often blow off while inflating inside the tyre! Always use the proper size tube.
06-14-02, 11:57 PM
Hmm, Interesting THEORY about a 25mm tube getting blown up enough in a 35 mm tire, (10mm difference), to make it so thin it's going to rupture. I've never seen it proven in nearly 30 years of riding and racing, including over eight years working in some VERY respected shops. It's also interesting that mechanics who've provided neutral support in several Olympic Trials or who've been assigned to work the "Giro" for their team have actually recommend using a smaller tube than tire to save weight, to make installation quicker and easier and less likely to have seating problems because of the reduced bulk to deal with.
I've used smaller tubes in my tires for DECADES with only POSITIVE results, imagine that!!! (I've used same sized tubes as well and PREFER to use the "skinny ones"). Of course there are limits, but, ( I believe), they're a bit more than 10 mm.
A tire "blowing off" of a rim is almost always the result of poor seating, usually when an edge of the tube is caught under the rim or when the rim isn't seated evenly around the rim. Also the "hook bead" problem mentioned above is definitly a cause as well.
I guess we all have different experiences and opinions and need to check the credibilty of our sources of infomation- I KNOW I'm not omniscient.
Ride with an open mind
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