The Great Debate: Mountain Bike Wheel Sizes

| Greg Hodges

Which is the best wheel size for a mountain bike? The traditional 26-inch wheel, the 650B/27.5-inch size or the larger 29-inch wheel? It’s a debate that generates fierce opinions, with strong advocates of all three wheel sizes.

Let’s take a look at the pros and cons of each size.

26-inch wheels

Not so many years ago, 26-inch wheels were a mountain biker’s only option. Whether riding cross country, enduro, downhill, or any other variant of the sport, everyone was riding 26-inch wheels.

Why? Well, advocates of other wheel sizes say that 26-inch wheels became the accepted standard by accident, as much as by design. The founding fathers of mountain biking in California hit the trails on beach cruisers with 26-inch wheels, and the size stuck. In the past decade, mountain-bike designers have questioned whether 26-inch wheels really are ideal—hence the new “better” sizes.

There are good reasons why 26-inch wheels shouldn’t be dismissed out of hand, though. With their smaller diameter and shorter spokes, all else being equal, a 26-inch wheel will be stronger than a 650B or 29er. The smallest of the big three wheel sizes is the lightest, too, which makes for snappier acceleration.

Spares are easy to find, with a huge choice of components built to the longest established of the three wheel sizes.

Handling is usually very nimble, especially compared with a bike designed around 29-inch wheels, with little inertia to get in the way of rapid direction changes.

However, 26-inch wheels tend to clatter into bumps and roll less smoothly than the other wheel sizes.

29-inch wheels

We’ll jump a size and consider 29-inch wheels, as these came next in the evolution of the mountain bike.

Because of their larger circumference, 29-inch wheels hit obstacles at a shallower angle than 26-inch wheels, so they roll over bumps better. The longer contact patch is another plus, and it helps a 29er find grip where 26-inch wheels struggle.

However, bikes with 29-inch wheels tend to have a different feel to those with 26-inch wheels. Early designs in particular were criticized for feeling slow to turn and less nimble than 26-inch bikes. Another downside is the extra weight of 29-inch wheels, which means they take more effort to accelerate. Their sheer size has made it a challenge for bike designers to combine 29-inch wheels with long-travel suspension, especially in small frame sizes.

As 29ers have become more widely accepted, some of these disadvantages have been addressed by adjusting frame and fork geometry to better suit the wheel size, combining smooth rolling and great traction with more entertaining handling.

650B or 27.5-inch wheels

The 650B (also known as 27.5-inch) wheel size promises the best of both worlds. In just a few short years, 650B has rapidly been accepted by the industry and MTB riders alike.

Compared with 26-inch designs, 650B wheels hit bumps at a shallower angle, so they roll better over rough terrain, although not as well as 29ers. Compared with 29-inch wheels, 650B are lighter and stronger, with punchier acceleration and sharper handling.

You’ll find a wide choice of trail and enduro bikes using the 650B wheel size. Specialist downhill bikes still commonly use 26-inch wheels, while 29-inch wheels have their strongest following among cross-country riders and racers.

Which is the best mountain-bike wheel size?

If a horses-for-courses answer seems like a cop out, then sorry. But it really does depend on the type of rider you are and the terrain you ride.

The original 26-inch wheel size hasn’t disappeared. For downhill bikes, which long-travel suspension is needed and wheels must be utterly bombproof, tough 26-inch wheels still make sense, although 27.5-inch bikes are making inroads.

According to research by the University of Central Lancashire, over an XC course 29-inch wheels are fastest. So, if cross-country racing is your thing, 29ers are hard to beat. They also make comfortable, smooth-rolling bikes for less technical riding.

But while 29ers may be fast, for general trail riding the new generation of 650B bikes is at the cutting edge of MTB design, combining agility, strength and traction in one compelling package.

So as we’ve seen, all three mountain bike wheel sizes still have their place. But if you had to pick one for maximum fun out on the trails, it would be the 650B.