Wheels are among the most confusing components you can buy for your mountain bike; there's a seemingly endless array of choices, all with their own set of claimed benefits.
Here's a straightforward primer to help you cut through the hype and figure out what will make the most sense for you – and your budget.
The first thing to think about is whether the wheels you're considering will actually fit on your bike. These days there are three prominent wheel diameters to choose from (26in, 27.5in/650b, and 29in) along with a number of different axle fittings. So-called 'quick release' hubs haven't changed much at all in recent years so if your bike is so equipped and the wheels you're considering bear a similar descriptor, chances are they'll be compatible.
Mountain bike wheels vary in terms of both diameter, rim width, and axle fittings. Rotor and cassette interfaces vary too
Thru-axles are a bit trickier, though. 142x12mm is most common for rear wheels and 100x15mm is the predominant format up front but several other variants still exist so be sure to check what your bike uses first and then go from there. The hubs on many wheelsets can be converted to different axle standards, too, so don't give up if your first choice doesn't initially appear to be compatible.
Lastly, be wary of the interface used to attach the disc brake rotor. There are just two standards available – Center Lock or six-bolt – and while the former can be adapted to the latter, it isn't the case the other way around.
Rotors attach via either a six-bolt pattern like this or with Shimano's Center Lock splined interface
Tubeless or not?
The debate between traditional wheel-and-tire setups that require an inner tube, and tubeless ones that can be run without is a hot topic these days with no clear consensus. Inner tubes are easy to install and inexpensive but tubeless setups are generally more resistant to flatting and can be run at lower pressures, which can boost traction and rider comfort.
Tubeless-compatible rims give you the option of using tubes or not
Regardless of which side of the fence you put yourself, it's a much easier decision when it comes to wheels. While non-tubeless wheels can be run tubeless with a little bit of work, tubeless wheels are not only ready to run but can be set up with or without inner tubes.
Moreover, some tubeless rim designs are also inherently stronger and more durable than traditional ones so there's little reason to pass over that feature.
Rims these days are trending wider (and keep in mind that the critical dimension here is internal rim width, not external). While 19mm used to be the standard for mountain bike wheels, the typical dimension is more like 21 to 23mm with some models going up to 30mm or more.
There's a good reason for this progression, too. As rim width increases, so does tire stability (particularly at lower inflation pressures), footprint size, and air volume – all of which bode well for traction. Those more generous cross-sections do typically carry a weight penalty, though, so keep your intended use in mind. Riders that place a higher premium on grip will likely tend to the wider end of the spectrum while cross-country racers will probably want to stick to the narrower end in order to save some weight.
More experienced riders who are more in tune with what they like in terms of tires should also keep in mind that wider rims will also flatten out a tire's cross-section. In other words, tires with round profiles on a narrower rim will have more of a squared-off shape on a wide rim. On the other hand, tires that already have squared-off shoulders can practically end up flat enough to let the bike stand up on its own depending on how wide you go. None of these situations is inherently bad, mind you, but it's something to keep in mind when you're shopping.
When shopping for new wheels, you'll occasionally come across references to engagement speed. This refers to how quickly the spring-loaded pawls catch on the ratchet teeth inside the rear hub when you start pedaling again after coasting, even for a split second.
How quickly a rear hub engages under power is usually related to the number of teeth on the drive ratchet
Lower numbers – or fewer degrees of rotation – are generally better here as pedaling inputs will turn into forward motion will less lag, which not only confers a sense of immediacy but can also make the difference between making it up a technical climb and walking.
Particularly quick-engaging hubs can often sound quite buzzy, however, so weigh that against your preferences for peace and quiet before you make your decision. Faster hubs also sometimes require more frequent maintenance as the finer ratchet teeth can't be as heavily loaded with lubricants.
Even if you'll regularly be heading uphill by means of a lift instead of pedal power, lighter wheels are generally preferred over heavier ones, all else being equal. The reduced mass not only equates to easier climbing but also quicker handling as there will be less of a gyroscopic effect to battle when changing directions. Even braking performance is improved as there's less rotational inertia.
Lower weight should never be pursued at the expense of your particular durability requirements, however, and of course, less is more when it comes to cost. Those lighter wheels are fun to ride but you'll also spend a pretty penny in the process.
Fancy, high-end wheels are fun to ride but they don't come cheap - and maintenance can potentially be expensive long-term, too
Durability and serviceability
Most wheels work great when new but it's only after you've started to really use them that durability comes into play. Keep your local riding conditions in mind when investigating bits like hub seals, rim materials, and even how the rims and hubs are joined together.
Riders in wet and muddy climes, for example, will want to put greater emphasis on quality seals and bearings that can be easily serviced and/or replaced as needed. Riders in drier climes who will regularly tackle unforgiving rocks, on the other hand, might want to seek heavier-duty rims with thicker extrusions or a higher spoke count.
Speaking of which, even the best wheels can be damaged in a crash and will eventually need maintenance regardless. Check to see if any special tools are required for servicing or if there are any proprietary spare parts used, such as bearings and spokes. Few things are more frustrating than waiting ages for a tiny replacement bit to arrive because it isn't available in any local shop.
And yes, of course, bear in mind your budget – but not just with the initial purchase price. Some companies offer optional repair or replacement policies for damaged wheels while others include discounts for crash replacements at no extra cost. Depending on your anticipated use (and your riding style), these might make sense. A little extra money spent up front could potentially mean much less spent later.