# Tolerance for bicycle tire width?

**URL:** <https://boards.straightdope.com/t/tolerance-for-bicycle-tire-width/947226>\
**Category:** Factual Questions\
**Created:** [July 24, 2021, 9:39pm UTC](https://boards.straightdope.com/t/tolerance-for-bicycle-tire-width/947226 "2021-07-24T21:39:34Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [July 30, 2021, 12:03pm UTC](https://boards.straightdope.com/t/tolerance-for-bicycle-tire-width/947226/21 "2021-07-30T12:03:36Z")

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It was my understanding that there’s no difference between those: Bikes are completely measured in metric, the diameter is exactly 700 mm, but that’s sometimes converted to American units and rounded to the nearest inch.

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**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\
**Post date:** [July 30, 2021, 1:13pm UTC](https://boards.straightdope.com/t/tolerance-for-bicycle-tire-width/947226/22 "2021-07-30T13:13:52Z")

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No not correct. As I say there is an 8mm difference. 630mm vs 622mm

[“The [27”] rim itself is slightly larger than modern 700c wheels, which has been learned the hard way by many of us after buying a new road tire and struggling to get it seated.”](https://www.montaguebikes.com/folding-bikes-blog/2019/06/bicycle-wheel-sizes-explained/)

You must be from the planet next door where bike wheel sizing makes some sort of sense. Believe me this ain’t that planet.

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