The Right Rim for Your Bike

The right rims ensure that your self-built wheelset is as well-rounded as possible. No matter what material they are made of, how wide or high the cross-section is and how many spokes you use, your rims should be chosen based on their ability to withstand loads, i.e., to suit your intended use and riding style. When it comes to load-bearing components, you must be able to rely on them consistently. A super-light XC rim is not worth much if it goes to pieces in a demanding enduro race. A rim for your road bike should be light and ideally aerodynamic, but it does not have to be able to take as many knocks as ones for a mountain bike. Durability is also an important consideration for an everyday bike. We’ll go over important aspects to keep in mind when choosing the right rim.

Find the right wheel size

Of course, the diameter of your rims should match your frame or overall bike build. Specifications such as 29 inch or 27.5 inch are rounded values of the outer tyre diameter. The matching rims are standardised at the tyre seat – the Bead Seat Diameter (BSD). The most important dimensions here are 

• 622 millimetres (for 28- and 29-inch tyres),
• 584 millimetres (for 27.5-inch tyres, often also called 650B) and
• 559 millimetres (for 26-inch tyres).

Within the guidelines set forth by ETRTO (European Tyre and Rim Technical Organisation), you will often find the measurement for rim diameter as it corresponds with the rim’s width.

The number of holes in the rim

When placing your order, make sure that you select rims with the correct number of spoke holes! The number must match the number on your hubs. In general, more spokes afford more stability and durability to your wheel. The trade-off for this is a slightly higher weight. While 32 or occasionally 28 spokes are common on mountain bikes, 24 or fewer are often used on road bikes. For a cargo bike or a touring bike loaded with a lot of luggage, it is well-advised to use 36 spokes or more. Eyelets in the spoke holes are intended to better distribute the tensile force of the spoke nipples. Today, however, rims with eyelets are rarely found, as modern aluminium alloys and carbon can also withstand the forces that directly occur. If a slight increase in weight does not bother you and if you place higher value on durability and stability, then there is nothing stopping you from choosing rims with eyelets or, as an alternative, nipple washers. With some rims, such as those from market leader DT Swiss, such washers are already included in the scope of delivery. You can find all details and information in our product descriptions.

Rim width and jaw width

In keeping with the trend towards wider tyres, wide rims have become popular both on- and off-road in recent years. Twenty years ago, mountain bikes often had rims that were as narrow as 17 to 19 millimetres, but today 25 or even over 30 millimetres are the norm in terms of width. Widths around 21 millimetres are no longer a rarity on road bikes. The rims on your gravel bike probably fall somewhere in between. We are not talking about the width of the rims on the outside, but about the so-called jaw width. This is the distance between the two rim flanks, i.e., the width measured on the inside. The width of the tyre determines how your tyre sits and impacts its cross-section. You can compare the cross-section of a wide tyre on a narrow rim with the shape of a pear. On a wide rim, however, the same tyre will build up more volume. The sidewalls do not converge as much but stand more upright and support the tyre better overall. This allows you to ride with lower air pressure before the tyre pops off in curves or on obstacles such as roots or kerbs. However, that does not mean that wider automatically equates to better. With the same stiffness and stability, wide rims are slightly heavier, so it’s important to find a good compromise. The rim must, of course, also match the tyre. If the rim is too narrow, the tyre’s tread will be pulled down further at the sides. The side lugs of a mountain bike tyre are then set at a different angle and only grip in curves at a significantly higher lean angle. If, on the other hand, the rim is too wide for the tyre, the tread will build up in a rather "angular" way and cannot function as designed by the manufacturer. This makes the transition from the tyre’s tread to the sidewall rather inharmonious. In the worst-case scenario, the grip can suddenly break off at high lean angles.

Rim depth correlates to aerodynamics

Rims with a greater level of depth are mainly found on time trial bikes. The deeper profile reduces stall and turbulence. However, you don't have to be a triathlete or time trialist to benefit from it. You can reach speeds where the difference is noticeable even when riding a normal road bike. The deeper your rims, the more streamlined your bike will be. Some manufacturers go one step further and design the surface of the rim like that of a golf ball, with lots of small and uniform indentations. These “dimples" help to reduce the drag coefficient and thus the air resistance even further. Aerodynamics specialist Zipp also reduces susceptibility to lateral wind forces with their patented Sawtooth™ rim design.

Lightweight construction vs. stability and durability

After the tyres, the rims endure more punishment than all other components on the bike. Durability and stability are therefore an important factor to consider. Rims that are too soft lose their concentricity more quickly or get dented when punctured. Furthermore, frequent load changes can cause spokes to break, even if the spoke tension is high enough. Stiffer rims provide a solution, but as previously discussed, these are often somewhat heavier and less comfortable.

Hookless rims

Until now, most rims had a hook on each of the flanks towards the inside to provide security against the tyre popping off. With the lower manufacturing tolerances of high-quality tyres and rims for tubeless use, quite a few rim manufacturers dispense with this mechanical safeguard. The mounted and inflated tyre does not have enough room to move to be able to pop off over the rim flank. So-called hookless rims are easier to manufacture in the case of carbon, save weight and promote a rounder tyre contour. With hookless rims, particular care should be taken to ensure that the rim and tyre widths match and that the air pressure is within the range recommended by the manufacturer. Otherwise, the tyre could come off, especially with narrow road bike tyres and high pressure.

What else to consider when building wheels

Lightweight rims and carbon rims in particular have a limit to the amount of spoke tension they can tolerate. For wheel building, make sure to use a tensiometer and follow the rim manufacturer's instructions! By the way, carbon rims are usually easier to true on concentricity, but rims made of modern aluminium alloys can also be worked with very well. Rim rings welded at the butt are a bit more fun in the truing stand than pinned ones because there is no edge. Make sure that the nipples protrude from the rim and can be tightened with a conventional spoke wrench, or if you have chosen rims where the nipples remain hidden in the hollow chamber. In this case you need a special spoke wrench to be able to turn them through the rim bed from above.