Quote:
Originally Posted by dddd
When you get even a tiny puncture in a tube that is highly stretched, the rate of air loss is going to be much higher than when the tube is only stretching slightly to fill the volume inside of the tire.
And near the valve stem, those skinny tubes will have only half of the circumference of the tube doing all of the stretching, since the thicker rubber pad around the base of the stem hardly stretches at all.
It gets much worse if the wide tire is mounted on a narrow rim, since the skinny tube inflates hard inside of the tire only, and pins itself inside of the tire by air pressure before narrow portion facing the rim cavity then has to stretch heavily to fill the rim cavity. Expect tube ruptures to either side of the stem reinforcement where the reinforcement will be especially resistant to falling between the tires beads (which are going to be only about 10mm apart).
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True but the OP is going to use a 25mm tube in a 28mm tire..not 'highly stretched'. 25mm tube will be fine..