Why are tires sometimes narrower than their listed size?
In order to ensure that tires have sufficient frame clearance, tire manufacturers generally prefer to keep production closer to the lower end of the permitted tolerance (+/- 3 mm).
Carcass casing materials have become more and more sophisticated over time. That reduces the tire widening after the fitting.
Furthermore, inflation pressure also plays a major role. With maximum inflation pressure the tire becomes wider than with low pressure. And a recently fitted tire still widens over time. This can make a difference of 1 to 2 mm.
The tire width is measured at the widest point, i.e. outside the lug.
It's Important to note that a tires mounted width is directly affected by the internal rim width of the wheel it is mounted on.
A larger internal rim width will yield a flatter cross-sectional tire profile.
Conversely, a smaller internal rim width results in a tire that is taller, but less wide.
See in the below tire schematics how a 40mm wide tire can be as narrow as 39mm on a 19mm internal width rim, but as wide as 45mm on a 25mm internal width rim:
When upgrading a tire, one should consider the internal rim width of their wheel as this will dictate if the new tire will be smaller, or larger then the width listed on the sidewall.
Carcass casing materials have become more and more sophisticated over time. That reduces the tire widening after the fitting.
Furthermore, inflation pressure also plays a major role. With maximum inflation pressure the tire becomes wider than with low pressure. And a recently fitted tire still widens over time. This can make a difference of 1 to 2 mm.
The tire width is measured at the widest point, i.e. outside the lug.
It's Important to note that a tires mounted width is directly affected by the internal rim width of the wheel it is mounted on.
A larger internal rim width will yield a flatter cross-sectional tire profile.
Conversely, a smaller internal rim width results in a tire that is taller, but less wide.
See in the below tire schematics how a 40mm wide tire can be as narrow as 39mm on a 19mm internal width rim, but as wide as 45mm on a 25mm internal width rim:
When upgrading a tire, one should consider the internal rim width of their wheel as this will dictate if the new tire will be smaller, or larger then the width listed on the sidewall.
Updated on: 07/19/2024
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