In this post, we discuss the importance of rim width and its effects on performance and safety.
One of the fundamental characteristics of a bicycle wheel, like tire size, is rim width. It will determine certain aspects of its performance while allowing one size or another to fit better to achieve maximum performance.
Rim width is more critical on mountain bikes than on road bikes. Although, in the latter case, with the increasing presence of tubeless tires, the choice of the proper width also becomes very decisive.
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Why should rim width matter?
Not all rim widths are suitable for the same bike, the same rider, or the same type of course. That’s why you should consider the different aspects below to identify the right size:
- Each tire has a recommended rim width: and vice versa. The rim and the tire go hand in hand within the wheel. The tire should have a suitable base to clamp or heel the wheel, and the rim width will provide the ideal shape for the tread.
Matching rim width to your tire size will affect bike stability, grip, handling, and ride comfort, among other things. However, other factors, such as tire pressure, compound type, lug shape, etc., also play a role.
The rim’s width influences the bike’s stiffness, stability, and comfort.
For example, tire brands have charts or graphs showing the recommended rim widths for each tire thickness. The rule is simple: the more wide the tire, the wider the rim should be.
- Identify the wheel type and its use: a large rim width will improve qualities such as high-speed stability, grip, and comfort and penalize weight, manoeuvring, or acceleration speed. For this reason, wide rims are essential in mountain biking. Especially in its most radical disciplines (enduro, downhill, etc.). Although in recent times, the practice of XC has also adopted extensive rims (30 mm) due to their versatility.
- There is an important influence on the weight of the bicycle: the wheel represents approximately 10 to 15% of the total weight of the bicycle. And a large part of this percentage is generated by the rim. It may seem insignificant, but 2 or 3 mm more in width means more metal must be used to make the rim. On average, and speaking of carbon models, for every 1mm increase in width, a rim weighs 7g more.
Internal width: standard rim size
Another factor to consider when judging rim width is that there are two rim widths: one is the outer, from the outer edge to the outer edge, and the other is the inner, from the end at the end of the central slot. The rim of the tire is placed at these ends.
Internal width has been the gold standard for measuring and comparing different bicycle rims for several years, especially since the popularization of tubeless tires. Thanks to this standard size, the brands, and the riders knew better how the tire fitted to the wheel and its lateral support. Greater internal width with the correct tire size provides better support to the wheel, avoiding the imbalance of the rims or the rubber.
The internal width determines the degree of lateral support of the tire.
Also, manufacturers can more accurately recommend either tire width using the internal width. Usually, a ratio of 2.2:1 is applied, i.e., an internal width X must have a tire 2.2 times that width. But this formula, which should only be used as a reference and not as a rule, can be modified by the rider by fitting wider or narrower tires according to his needs.
Rim width according to the type of cycling: MTB, road, and gravel
After reviewing the theory, there is an internal reference width for every type and discipline of cycling in practice. Here are the current standards:
XC: 30mm. Within mountain biking, there are different sizes of rims depending on the discipline practised. In Cross Country, internal widths have been increased from 19mm to 30mm (although 25 or 27mm are also widely used). More than a centimetre per rim. The increasing lightness of the materials used, as well as the improvement of designs, the oversizing of frames, axles, hubs, and manufacturing processes have allowed XC wheels, which must be light and fast, to add the advantages of a wide rim already mentioned (stiffness, stability, traction).
Trail/Enduro: 30-35mm. 30mm was the property of the most radical mountain bikes of the last decade. But in Trail and Enduro, tire width has also increased recently, to 2.5″; and 2.6″; which requires an increase in rim size to 35mm. This site has also taken off thanks to the rise of long-travel e-MTBs.
Drop: 35mm. Extending the 29er diameter from XC or Trail to Downhill has also led to oversizing the rims to withstand better the more significant impact and inertia of these wheels and to provide a higher level of stability.
Related article: Everything you need to know to buy mountain bike wheels
On the road, 23mm is becoming increasingly popular. But 19mm and 21mm are still very common. Unlike mountain biking, on-the-road internal width is a more secondary measurement in importance, especially when compared to profile or sidewall width. But in recent years, its importance has also grown sharply.
From 13 or 15 mm in recent decades, the internal width has doubled to reach 23 or even 25 mm. The centre notch looks like a mountain bike wheel from 8 or 10 years ago. Everything you need to get the most out of 28, 30, or 32mm tubeless or tube tires.
In gravel, the evolution of its components is constant, and the wheels are no exception. As in the rest of the discipline, they have gone from an initial standard of 19 to 20 mm to increase to 23 or 25 mm, depending on the case. All this to better fit and get the most out of 45 and even 50mm wide tires.
Conclusions: the rim-tire ratio is the key to choosing the correct width
We have seen that the rim and tire can only be chosen together. You may have purchased the most advanced rims on the market, with an oversized width and a profile that cuts through the wind like no other. But if you don’t choose the correct tire size for the width, you won’t be able to ride with maximum efficiency, which will affect comfort, premature tire wear, and the risk of wheel spin.
We recommend that you keep up to date with the most commonly used internal width standards for each type of bike. You should also consult the data sheets, and the tables of the tires recommended for each rim model. And when in doubt, apply the 2.2:1 formula to have a reference point on the ideal tire size.