Mountain Biking - Undersized Tube?
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11-15-04, 06:36 PM
Ok, this is one of those questions that a person shouldn't probably even be asking, but I did it, so I will. My apologies if it's already been asked, I looked around but couldn't find anything.
Anyhow, I just swapped out a 1.75" tire on my front wheel for a beefier 2.1" looking ahead to some fun snow biking this winter. Well lo and behold I didn't have any 1.75/2.1 tubes on hand, only a few 1.5/1.75. So I went ahead and stuffed in the smaller tube and inflated to full pressure . Took it out for a few miles to test everything out (did a bunch of diddling so I had to check all my work, you know how it goes). Anyhow, it all seems cool. Am I taunting the latex gods going with the smaller tube or is it no big thing?
11-15-04, 06:51 PM
A smaller sized tube will work, but you will be more open to pinch flats.
11-15-04, 07:38 PM
Am I taunting the latex gods going with the smaller tube or is it no big thing?
yes, pheer their wrath just as i taunt Raiyn's by typing "pheer"!
but think of it like over-inflating a baloon or better analogy an exercise ball, then bouncing it up and down (or rather bouncing ON it up and down) overstress the seams and rubber walls and they may give way, but in any case you make the walls stretch thinner and easier to break
11-15-04, 07:47 PM
Yeah, I thought of that, but the way I figure, in all cases it's really the tire casing that's keeping the tube from bursting. Under 50 lbs of pressure in open air any bike tube's gonna pop. So as long as I don't rip the seams it should hold--the thin tube walls don't really matter because tire will keep them "in". Of course getting it up to pressure and riding for a few miles is no guarantee that it's not going to rip out the seams later on. I guess I'm figuring it's sort of like tire inflation designation: it's all over engineered. For tires you go to blowoff pressure and then chop that number way down and you have your stamped max pressure. For tubes you build for a certain diameter assuming that the crappiest of the crappy tubes that might come off the assembly line will be able to hold up that size. Right? :)
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