The sizes you commonly see for mountain bike wheels like 26in 27 5in and 29in all refer to the outside diameter of the wheel with the tire fully inflated.
Mountain bike tire width sizes.
Tires come in three diameters.
Trail and all mountain bikes will have tires in the 2 25 to 2 4 width range.
Downhill bikes which are meant to withstand the abuse of drops and rock gardens are typically equipped with tires up to 2 5 wide.
Typical mountain bike tire.
Mountain bike tire size and width.
Check your tire s sidewall the numbers there indicate your tire size roughly its outer diameter and its width but not always in that order.
26 inches 27 5 inches and 29 inches.
2 2 and 27 5 indicate a tire that has a width of 2 2 and an outer diameter of 27 5.
These sizes can be thought of as a sort of shorthand for decimal sizes each with a corresponding iso measurement.
This varies from 1 6 to 2 5 inches.
Tires are also measured in width.