The rim width is an important factor when choosing the wheels for our bike. Not all tires are suitable for all sizes, and getting it right affects the overall performance of our machine. We could say that rim width is a very important value in the MTB
category. But it is also true that in Road
cycling, it is becoming very relevant due to the growing adoption of tubeless tires.
Why you should pay attention to rim width
As we said, not all rim widths are suitable for the same bike, cyclist, or type of route. To identify the right size, you must consider some aspects. Each tire has a recommended rim width, and vice versa. The rim and the tire work together as a unit within the wheel. The tire must have the proper base to attach or seat on the wheel; the rim width will give the ideal shape to the tread. Mounting a rim width adapted to the tire size will contribute to the bike's stability, grip, traction, and riding comfort. Although other factors also come into play here, such as pressure, compound type, tread pattern, etc.
The rim width affects aspects such as the stiffness, stability, and comfort of the bike.
Tire brands, as well as wheel brands, have tables or charts with the recommended rim widths for each tire thickness. The equation is simple: the wider the tire, the wider the rim.
Identify the type of wheel and its use. A large rim width will enhance qualities such as high-speed stability, grip, and comfort, but it will also penalize weight, maneuverability, or acceleration. That’s why wide rims are essential in the most extreme MTB disciplines (enduro, downhill, etc.). In any case, the XC discipline has also adopted very wide rims (30 mm), given their versatility. The rim significantly influences the weight of the bike. In general, the wheel accounts for about 10–15% of the total weight of the bike. Of this percentage, a good portion belongs to the rim. It may seem insignificant, but 2 or 3 mm more width means using more metal to make the rim. On average, and speaking of carbon models, for each 1 mm increase in width, a rim will weigh 7 g more.
Internal width: the standard measurement for rims
Another factor you should take into account when assessing rim width is that it has two measurements: the external width and the internal width. The external width is the measurement from outer edge to outer edge. The internal width, on the other hand, is measured from edge to edge of the central groove, where the tire bead is placed. The internal width is the standard reference for measuring and comparing different bicycle rims. Especially since the popularization of tubeless tires. This way, both brands and cyclists can predict how the tire fits on the wheel and what degree of lateral support it has. A greater internal width provides, with the right tire size, better support for the wheel; it prevents pinch flats or rubber imbalances.
The internal width determines the degree of lateral support for the tire.
Using the internal width allows manufacturers to recommend a tire width with greater precision. Normally, a 2.2:1 ratio is used. That is, an internal width X should have a tire 2.2 times wider than that width. In any case, this formula is a guideline. The cyclist can adapt it according to their needs, fitting wider or narrower tires.
Rim width according to cycling discipline: MTB, road, and gravel
There is a reference internal width for each cycling discipline. Do you want to know what the current standards are depending on the type of cycling we practice?
Mountain Bike
XC
: 30 mm. Depending on the MTB discipline practiced, there are different rim sizes. In Cross Country, internal widths have increased from 19 mm to 30 mm (although 25 or 27 mm are also common). Lighter materials and improvements in design (oversized frames, axles, hubs, and manufacturing processes) now allow XC wheels, which need to be light and fast, to take advantage of the already mentioned benefits of a wide rim (stiffness, stability, traction).
Trail/Enduro: 30 – 35 mm. The 30 mm width has been owned by the most radical MTBs in the last decade. But both in Trail
and in Enduro
the width of the tires has also increased in recent times, to 2.5" and 2.6". This requires increasing the rim size up to 35 mm. This size has also taken off thanks to the boom of long-travel electric MTBs.
Downhill
: 35 mm. The Downhill modality has also adopted the 29'' diameter for its tires, which has led to oversized rims. In this way, they better withstand the greater impacts and inertia of these wheels, gaining in stability.
🏔️ Everything you need to know to buy mountain bike wheels
Road
In Road
the standard is 23 mm, but 19 mm and 21 mm are still very common. In this modality, unlike MTB, the internal width is a less decisive measure; especially if we compare it with the profile or width of the sidewall. [irp posts="4019" name="Tips for buying the right wheels for a road bike"] From the 13 or 15 mm of past decades, the internal width has doubled to 23 or even 25 mm. The central groove is now like an MTB wheel from 8 or 10 years ago. The goal is to extract the maximum performance from tubeless or tube tires of 28, 30, or 32 mm.
Gravel
The evolution of components for Gravel
never stops and wheels are no exception. Starting from an initial standard of 19 to 20 mm, it has gone up to 23 or 25 mm, depending on the case. All to better accommodate, and make the most of, 45 or even 50 mm wide tires.
The rim-tire relationship, key to choosing the width
We have seen the importance of choosing rim and tire together, and not as separate elements. You may have bought the most advanced rims on the market, with an oversized width and a super-aerodynamic profile. But if you make a mistake when choosing tire width, you will lose efficiency. Not to mention the loss of comfort, the possibility of premature wear, and even the risk of unseating. That’s why we recommend keeping up to date with the most commonly used internal width standards for each cycling modality. You can also check the technical sheets and recommended tire charts for each rim model. If in doubt, you can always apply the 2.2:1 formula as a reference point to determine the ideal tire size for your wheels.