MTB wheels are often forgotten as a performance item, but upgraded wheels can make all the difference in your ride. With so much focus on suspension, tread patterns, and air pressure, that the things supporting the tire are overlooked. The width of the rim affects effective width of the tire, which impacts the footprint, which impacts air pressure. Hubs have two to four bearing races in them, and how they roll impacts efficiency. The spokes, spoke dimensions, and spoke pattern affect wheel strength, which can matter not only when taking hits, but carving turns. And, of course, weight matters; lighter goes uphill better and accelerates faster, while heavier goes downhill better and holds speed more easily.
Thanks to rotor disc braking, mountain bike rims got shorter sidewalls. With the short sidewalls, rims got stronger in general, making it much easier for carbon mountain bike wheels to become practical. Shorter walls = less unsupported weight, which generally leads to stronger sidewalls, lighter rims. This has helped make carbon-rimmed wheels more popular—lighter is only a benefit when you know that the rim is likely to finish the ride. Reynolds MTB wheels were among the first to embrace carbon for the dirty discipline, and their experience shows. ENVE came late with their MTB wheels, but their innovative thinking helped them leap into the lead group.
Still the best mountain bike wheels are the ones you’re happiest riding. Carbon is great, but if they seem too spendy or if you expect to break stuff, aluminum mtb wheels are nearly as impressive and don’t lead to tears. DT Swiss, like several companies, offers practically identically spec’ed wheels in both carbon-fiber and aluminum, so it is easy to make direct comparisons when trying to determine the price-benefit analysis of carbon vs. aluminum.
29er wheels seem big, but they’re actually just wide 700c, and have been around since the earliest days of mtb. They roll better, have gotten stronger and lighter, and are the xc preferred choice.
The 27.5” size, or 650b if you’re old-school, sits halfway between 26” and 29”. Therein lies the charm. Better-rolling than 26”, stronger than 29”, they make geometry easier for smaller folks as well as for bikes with long travel. Race Face, like Bontrager, and many others, offers 27.5” wheels in both aluminum and carbon versions so you can weigh the differences.