If the external diameter of the rim is 23mm, there’s a high chance that a 25mm tire can be installed on it without issues. If the internal diameter of the rim is 23mm, then the rim is too wide for a 25mm tire.
External Rim Width
The external width of the rim is the perpendicular distance between the outer sides of the rim’s walls. Or in simpler words, the external width is the total rim width.
Internal Rim Width
The internal rim width represents the perpendicular distance between the closest inner points of the rim.
The internal width is the number used most frequently to specify a rim’s width because it indicates the size of the tires that the rim can safely accept.
Rim and Tire Sizes
The table below is a guideline showing the tire size that rims can accept depending on inner rim width.
| 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 |
Conclusions
The data from the table reveals:
- A rim with a 23mm internal width is best combined with a 37-68mm tire. Consequently, it will be unwise to use the rim with a 25mm tire.
- A 25mm tire requires a rim with internal width ranging between 13mm and 17-18mm. If the rim in question has a 23mm external width, then there’s a very good chance that its internal width is within the aforementioned range. In that case, the user will be able to combine the rim with a 25mm tire.
FAQ: What are the downsides of combining a tire with an excessively wide rim?
If a wide rim is equipped with a tire that’s too narrow for it, the user is risking:
- Damage to the rim due to insufficient protection from the tire, especially when riding on uneven terrain.
- Pinch flats (A puncture that occurs when the wheel hits a dull but hard object.)
If The Number 23 Indicates The Tire Size…
It’s possible that you know neither the inner nor the external width of the rim and the 23mm measurement indicates the actual tire size. In that case, you will have to measure the external diameter after deflating the tire and subtract a couple of millimeters from it to come up with an approximate inner width that will serve as a guideline.
Of course, the best and most accurate option will be to remove the tire and measure the inner width directly.
If the wheels have been equipped with 23mm by default, chances are that the inner rim width is 14-16mm.
The Advantages of Switching From 23mm to 25mm Tires
- Softer Ride
25mm tires are wider and can therefore operate at lower air pressure without risking pinch flats. Consequently, the tire has an easier time absorbing road irregularities and provides a smoother ride that reduces the stress on the rider’s joints.
- Extra Traction
When two tires have the same tread pattern, the wider model provides greater traction thanks to the larger contact patch. The extra traction results in stability and allows the rider to cover less than ideal roads.
- Lower Chances of a Trapped Wheel
Thinner tires can fall into a crack or a water drain if the rider isn’t careful. When that happens a fall over the handlebars is close to 100% guaranteed. 25m tires are also subject to the same problem but not as much as 23mm models. Thus, 25mm tires are better for commuting from that perspective.
The Downsides of Switching From 23mm Tires To 25mm Tires
- Drag
The profile of wider tires results in extra drag. That said, the effect is inconsequential to recreational riders.
- Extra Weight
Wider tires weigh more due to the extra material used for their production. Nonetheless, the extra grams are too little to matter unless one is trying to assemble the lightest possible bike.
- Reduced Clearance
If the bike is an aggressive road or track model a set of 25mm tires can greatly reduce its clearance and completely prevent the usage of accessories such as full fenders. For serious commuters, this could be a big deal.
Summary: What You Need To Know
- If the internal rim width is 23mm, then the rim is too wide for the safe usage of 25mm tires.
- If the external rim width is 23mm and the internal width falls between 13 and 18mm, then the rim is very likely to accept a 25mm tire without issues.
- Switching from 23mm to 25mm tires offers the following advantages – softer ride, extra traction and a wheel less susceptible to falling into a crack.
- The disadvantages of switching from 23mm to 25mm tires are – extra drag, weight, and reduced clearance.
