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Tube Size Mix-Up

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I replaced my tires with new D606s for an upcoming trip along the CDT. The rear tire is the stock size 120/90-18. The tube I was sold is a 100/100-18 Bridgestone UHD. The previously installed tube is a 110/100-18 which is the correct size.

What is likely to happen with a 1-size too small tube, and under what conditions? E.g. is it likely to fail under sustained high speed riding?

Ian

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not an issue, I've run that size for while with a 120/90-18 DOT knobby.

I've also run about the same size tube with a 19" diameter, no issues, easier to install, imo.

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There is quite a but of latitude in tube size but 120 is quite a bit larger than 100. Consider the 100 tube has to stretch to fit the100, it has to stretch a lot more to fit a 120. What is likely to happen is probably nothing . But if you get a puncture, the tube is more likely to rip at the point of the puncture. Possibly deflate more quickly. Possibly unable to patch the puncture.

Also ultra heavy duty tubes are not really intended for high speeds.

Personally I use high quality standard tubes of the recommended size.

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There is quite a but of latitude in tube size but 120 is quite a bit larger than 100. Consider the 100 tube has to stretch to fit the100, it has to stretch a lot more to fit a 120. What is likely to happen is probably nothing . But if you get a puncture, the tube is more likely to rip at the point of the puncture. Possibly deflate more quickly. Possibly unable to patch the puncture.

Also ultra heavy duty tubes are not really intended for high speeds.

Personally I use high quality standard tubes of the recommended size.

The appropriate numbers to compare are actually a combination of width and aspect ratio, not just the width.

E.g. a 100/100 tire can be thought of as having a cross-sectional area of 10,000 (i.e 100 x 100); a 110/100 tube would be 11,000. A 120/90 tire has an area of 10,800; and a 120/80 tire has an area of 9,600. The appropriate tube for a 120/90 tire is 110/100; and the appropriate tube for a 120/80 tire is 100/100.

So a 100/100 tube is the appropriate size for a 120 wide tire as long as the aspect ratio is 80, but is 1-size too small (or at least smaller than optimum) for 120/90 tire.

Ian

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