Bicycle tires
Measurements are a jungle, not only due to historically dishonest marketing, but also because by convention the inch-measurements go by the expected approximate outside diameter of tires, so a tyre fitting a 622mm wheel is marked as a 28" tyre if it goes on a narrow (road bike) wheel, and marked as a 29" tyre if it goes on a wide (mountain bike) wheel. The wheels themselves have the same diameter.
Minimize confusion by using the ISO standard, which measures wheel diameter in millimeters regardless of the tires. All tires fitting a 622mm wheel are marked the same. And then you see the tyre width as a separate number. If you read a number like 32-622 on a tyre, that means it's about 32 mm wide at full pump. If you read the same number on a wheel, that means it's intended for such tyres (the actual metal rim can be narrower).
Here are the diameters you can expect to see in Swedish outlets today:
- 559 mm - called 26" on MTB
- 584 mm - called 27.5" on MTB
- 622 mm - called 29" on MTB and 28" on road bike