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Saw two different tires. One marked 700c 38mm 40 622 measured 1.25 " wide.Other tire ,same markings but with addition of marking, one and five eighths x one and a half,measured 1.5" wide. If both 38mm wide why quarter inch difference in width?

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    Tire manufacturers play it a bit fast and loose with tire widths. The stated width is when mounted on a rim of "nominal" width which they select, and a different rim width will result in a different measured tire width. You'll notice that the first tire is stated to be 38mm wide, then 40mm wide (the ISO width), but measured 32mm (the 1.25" width), presumably because it was mounted on a very narrow rim. This is one area that has not been very well standardized. – Daniel R Hicks Sep 9 '16 at 19:18
  • Welcome to Bicycles @Rob. We recommend that new members take the tour to make best use of the site, and since you're asking How to Ask is worthwhile also. The question you've asked is very common, so do check out the answers to the "duplicate". It's not the question so much as it's answers you should pay attention to " – andy256 Sep 11 '16 at 9:10
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Tire sizing can be very confusing. The late, great Sheldon Brown has written a web page that does a magnificent job of answering your question.

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