Condensed Answer: 2.6″ tires can technically be installed on rims with 40mm internal width, but in most cases, they will be too narrow.
40mm rims are designed for 3″ or wider tires. The main downsides of installing 2.6″ tires on a 40mm rim are the squared profile of the tire and the potentially difficult mounting process.
Internal Rim Width
Rims have two widths – external and internal. The external width, as the name suggests, is the total width of the rim from one outer edge to the other.
The internal rim width is the distance between the bead hooks. In most cases, manufacturers indicate only the internal rim width as it directly affects the tires that the rim is compatible with.
Note: The bead hooks are the parts of the rim to which the standard clincher tire mounts.
A Formula For Determining Rim and Tire Compatibility Based On Width
To find out the range of tires that a rim is compatible with, one can multiply the inner rim width by 2-2.3.
If the rim has a 40mm internal rim width, then it’s ideally paired with 3.2″ to 3.7″ tires.
The short table below is based on the same formula:
|Inner Rim Width
Note: The numbers in the table above are guidelines. Some deviation is allowed and expected because the size of most tires isn’t incredibly accurate. For example, a 2.6″ model from one brand could be wider or narrower than the equivalent unit from another manufacturer.
The Downsides Of Installing a 2.6″ Tire On a 40mm Rim
When a tire is narrower than the size intended for the rim, we observe the following side effects:
- Square Shape
Normally, tires have the shape of a bulb. However, when the rim is wider than expected, it stretches the tire. As a result, the tire’s shape gets closer to a square. A square tire is not necessarily harmful, but its shape is technically not optimal.
- Difficult Installation
The tire has to be stretched more to mount it on the rim. With some rim and tire models, this could be a major issue, especially if the rider isn’t equipped with adequate tire levers and doesn’t have experience with mounting tight tires on wide rims.
- Reduced Tire Retention
When the rim is wider than necessary, it can’t retain the tire as strongly as the proper rim because there’s less tension. This doesn’t necessarily mean that the tire will fall off, of course, but it’s still a downside that has to be mentioned.
Summary: What You Need To Know
- A 2.6″ tire can technically be installed on a 40mm rim, but in most cases, it’s too narrow. The solution is to get another tire that’s at least 3″ or a narrower rim.
The downsides of installing a 2.6″ tire on a 40mm rim are:
a. Square profile that hurts the originally intended shape of the tire
b. Difficult tire installation
c. Reduced tire retention