Mountain bike wheel standards

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A bike’s wheels represent one of its most important components, influencing acceleration, weight and stability. Depending on the configuration you choose, your bicycle’s performances can be significantly boosted if you pick the proper line-up. That’s why we’ll take a closer look at rim standards, quick release mechanism and even spokes, in order to aid you in your search for the best possible combination.

Sizes

For the moment, the 3 main sizes mountain bikes are dealing with are the 26, 27.5 and 29 inch ones, with some models rarely using the 24-inch standard.

Rim types

The classic rim features outer cuttings in order to accomodate the spoke’s nipples. After mounting and tightening the spokes, a rim band is layed over them which will prevent any damage to the inner tube once it is inflated to its optimal pressure. These rims are currently manufactured either from aluminum, either from carbon.

The tubeless rim doesn’t have any holes for the nipples on the outside for the fact that it doesn’t use an inner tube, and must be airtight in order to prevent air from leaking out especially through the contact area of the tires and wall. Also the walls of this kind of rim are a bit different from the classical one, and use a special type of valve.

The tubular rim is no different than the one used for the road tubular tires, having no sidewalls for the fact that the tubular tire is glued to it. A great advantage stands in its low weight, but also in almost completely eliminating the risk of a snakebyte puncture.

Aluminum rim vs. Carbon rim. Carbon’s perks are clear, having a low gram count, and a greater stiffness, but they’re more expensive also, and tend to be easier to damage. In mountainbiking, they stand as the first choice of cross-country riders, but they’re making their way in other disciplines, like enduro. For about half the money you’d pay for a carbon rim, you can get an aluminum alloy rim, which won’t choke your wallet in case it needs replacing.

Rim widths and tire compatibility

Basicly, the wider the rim is, the better the tire fits into or onto it, offering increased stability. On the other hand, it’s virtually impossible to mount a wide tire on a narrow rim, and the other way around. So, for 17 or 19mm-wide rims, you’ll have to pick a 2-inch wide tire, even more so if you plan on reaching a low weight. Another important thing is that rim width values refer to the inner width of the rim. Below we’ve made up a short table of compatibility for different rim and tire widths.

Tire width (inches)

Rim width           1.8          1.9          2.0          2.1          2.25       2.35       2.4

17 mm                 Yes          Yes          OK          No          No          No          No

19 mm                 Yes          Yes          Yes        Yes         Yes        Yes        OK

21 mm                 Yes          Yes          Yes        Yes         Yes        Yes        Yes

23 mm                 Yes         Yes          Yes        Yes         Yes        Yes        Yes

25 mm                 OK          Yes          Yes         Yes         Yes        Yes        Yes

27 mm                 No          OK           Yes         Yes         Yes         Yes        Yes

29 mm                 No          No          No          OK             Yes         Yes        Yes

Spokes

Several types of spokes are currently used:

  • classic ones with a curved head, made from steel,
  • butted ones, thicker at ends and thinner in the middle,
  • straight pull spokes, that increase the usage time, but require special hubs,
  • aero bladed spokes that offer greater aerodynamics

A wheel’s stiffness is influenced by the spoke pattern, different manufacturers opting for different schemes. For examples, the old-school pattern includes 3 contact points – one with the hub and the other 2 with other spokes, while other companies, such as Mavic use a cross-pattern for the driveside of the rear wheel, and a radial pattern for the non-drive side of it and for the front wheel.

Nipples

Attaching the spokes to the rim is made through small pieces named nipples, which are usually made out of aluminum or steel. The latter ones, though having extra grams, and rusting in time, support more servicing, while the sole advantage of aluminum nipples is they will save you roughly 20 grams/wheel.

Quick release axle

These mechanism come into use when mounting or unmounting your wheel, and recently became available in a larger and larger number of standards. The most common QR axle is the 9mm one, both for the rear and the front wheel, with widths of 135mm, respectively 100mm.

Front wheels may have different QR axles, depending on the suspension fork present, namely a 15mm diameter and 100mm width, or a 20mm diameter and a 110mm width. Of course, the bigger the diameter, the greater the stiffness, but both two offer a better stiffness by the simple fact they are screwed directly into the fork. A corresponding system is available for the rear wheel, only having one diameter – 12mm – and several widths: 135, 142 and 150mm.

The best wheelset

You can opt either for an already existent wheelset, or you can build-up you very own, piece by piece, but the best deal, almost all of the time, will be the first.

As far as hubs go, you can either pick the bearing ones (increased durability) or the loose ball bearing ones (lower weight), with a third option embodied by the ceramic hubs, which will cost you a good deal of money. The butted spokes are the best choice if you really mind the weight, but it’s probable they’ll set you back in terms of stiffness when it comes to the rear wheel. Our favorites in terms of QR axles are the QR15 for the front wheel, and the QR12 for the rear one, yet these two will require compatible forks and frames.

The ideal weight of a wheelset

The lesser, the better, of course, but this is not always easy to reach. A narrower set of rims and tires, a pair of loose ball bearing hubs, and a pair of lightweight inner tubes will normally do the trick, but this design has its drawbacks which include decreased confort or increased risk of puncture. Basicly, without the sprocket cassette, a pair of competitive cross-country wheels will tip the scale at 2,3 kilograms, QR, tires and tubes included.

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