This is a weird post Mark
Everyone knows this.
Doesn’t really mean much though.
I say actual measured width when mounted on your set up is a more important piece of information than what the tire says on the side. You disagree?
When we have real tire on a real rim it isn’t “how long is a piece of string” it is grab some calipers and measure your tire.
The actual measured width tells us more about all the things we might want to know (volume, aerodynamics and contact patch). It is in no way perfect though. Two tires/rim combos with the same measured width could/will have different volume and profile but it is better than what the tire has printed on the side.
Quote:
Originally Posted by Mark McM
Well, not exactly. Because if 25mm tires were actually 27mm tire, then they would also be 23mm tires.
A clincher tire casing does not create a complete pressure vessel, so its inflated width depends on the rim it is mounted on. The labeled width of a tire is based on being installed on a reference rim. If you install the tire on a rim wider than the reference rim, it will inflate wider the label width, and if you install the tire on a rim narrower than the reference rim, it will inflate narrower than the label width. Currently, ETRTO says you can install a 25mm tire on a rim width from 15 mm - 23mm, although previously they said 13 mm - 17mm. A tire labeled 25mm will inflate to an actual 25mm width on a rim about 17mm wide. On a 13mm rim they will be closer to 23mm, and on a 21mm rim they will be about 27mm.
So, the answer to "how wide is a 25mm tire" is similar to the answer for "how long is a piece of string."
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