Condensed Answer:
If the rim has а 25mm external width, then there’s a high chance that it will work just fine with a 23mm tire.
If the internal rim width is 25mm, then the rim is excessively wide, by conventional standards, for a 23mm tire.
External and Internal Rim Width
The external width of the rim represents the perpendicular distance between the outer sides of the rim. Or in simpler words, the external rim width is the total rim width.
The internal rim width is the perpendicular distance between the bead hooks. The bead hooks are the parts of the rim to which a clincher tire attaches.
Note: In most cases, the rim description indicates the inner rim width because it has a direct impact on the tire size that the rim can accept. Sometimes people add the letter “i” to indicate the internal rim width (e.g., i30).
Rim and Tire Compatibility Chart (conservative)
The table below shows tire and inner rim width compatibility. The numbers are on the conservative side and some deviations are allowed.
| INNER RIM WIDTH | COMPATIBLE TIRE SIZES (MM) | COMPATIBLE TIRE SIZES (IN) |
| 13-14.9mm | 18-25mm | 0.7-1in. |
| 15-16.9mm | 23-33mm | 0.9-1.3in |
| 17-18.9mm | 25-50mm | 1-1.95in |
| 19-20.9mm | 28-62mm | 1.1-2.5in |
| 21-22.9mm | 35-62mm | 1.35-2.5in |
| 23-24.9mm | 37-68mm | 1.45-2.7in |
| 25-26.9mm | 44-76mm | 1.7-3in |
The data reveals that a 23mm tire requires a rim with 13-17mm internal rim width.
Meanwhile, a rim with a 25mm internal rim width is coupled with a much larger tire (44-76mm).
That said, some deviations are expected because tires rarely have accurate dimensions. A 23mm tire from one manufacturer could be wider than the 23mm model of another producer.
FAQ: What is the internal width of my rim?
If you don’t know the internal rim width of your rim, there are 2 ways to find it:
a. Search for the technical specifications of your rim.
b. Measure the distance yourself. The ideal tool for the job is a digital caliper.
In most cases, the difference between the internal and external rim width is about 4-6mm. Of course, this value depends on the rim model and its thickness.
What are the dangers of combining a narrow rim with a very wide tire?
If a narrow rim is coupled with a rim that’s too wide, one risks the following:
Note: Whether the downsides below will manifest to a noticeable degree depends on three main factors – the tire and rim models as well as the air pressure.
- Flat Crown
Narrow rims result in “pointier tires”. Wide rims, on the other hand, stretch the tire and create a flat top/crown. Consequently, more of the tire comes in contact with the ground, and the tire squares off faster.
Or in simpler terms, the tire has a flatter contact patch resulting in more friction and faster wear.
- Extra Width
The width of the rim influences the effective width of the tire. For example, a 23mm tire could measure 23mm when installed on a 15mm rim but go to 25mm when put on a 21mm rim. The extra width could be a problem if the bike has limited tire clearance and/or uses full fenders.
- Side Wall Damage
A wider rim brings the side walls of the tire closer to the ground and increases the chance of damaging them. The side walls are made thinner because they have to be flexible. The reduced amount of material makes the sidewalls weaker and more susceptible to a puncture.
- Reduced Cushioning
A wider rim makes the tire flatter and consequently reduces the distance between the rim and the ground. One of the outcomes is a harsher ride because the tire doesn’t have the same room to change its shape upon meeting an obstacle.
- More Rim Stress
The reduced distance between the ground and the rim increases the stress on the rim and the inner tube.
As a result, it’s more likely to damage the rim and/or get a flat tire resulting from forceful contact between the rim and the tube upon meeting an obstacle.
- Sluggish Cornering
Skinny tires on a wider rim result in a flatter cross-section which hurts the cornering capabilities of the bike. (Normally, tires have the shape of a light bulb which makes cornering faster and easier to finetune.)
- Difficult Installation
Putting a narrow tire on a wider-than-usual rim could be a very difficult process. The wider the rim, the more the tire has to be stretched. Some tire and rim combinations could make the mounting process incredibly frustrating.
Summary: What You Need To Know
A 23mm tire can be mounted on a 25mm rim when the number indicates the external width. Ideally, the internal width of the rim will be under 20mm.
If the rim has a 25mm internal width, it’s too wide for a 23mm tire. Combining a narrow tire with an excessively wide rim has the following downsides.
- Faster tire wear
- Exposed side walls
- Less than ideal cornering
- More stress on the rim
- Wider effective tire width (reduced clearance)
- Difficult tire installation
