Mountain biking is currently in the throes of a technical shift as the wheel size we’ve used since the 70s is joined or supplanted – depending on who you believe – by another two sizes.
Mountain bikes have had 26-inch wheels since the original clunkers were constructed from adapted Schwinn beach cruisers. Nobody took a conscious decision to use that size rather than any other, though. Mountain bikes needed really fat tyres for traction and cushioning and tyres over two inches wide only came in 26in.
About ten years ago, a few pioneers started experimenting with larger wheels, building mountain bikes with the 700C wheels used on road bikes. With a two-inch tyre these wheels end up about 29 inches from tread to tread and the wheels gave the new bikes their name: 29-inch bikes, 29ers for short.
A ten year argument followed about the advantages and disadvantages of the new size. Evangelists made bold, often excessive claims about the faster and increased traction of the larger wheels, while sceptics rubbished 29-inch bikes for being ponderous and heavy.
The consensus that’s emerged in the last few years goes like this.
- Faster: Larger wheels roll faster, that’s a matter of the physics of tyres.
- Smooth Ride: They are also less prone to fall into holes in the trail, so a 29er smooths out the ride.
- Improved Traction: Because the tyre’s contact patch is longer, there are usually a couple of extra tyre tread blocks in contact with the ground, so traction is slightly improved.
Those advantages make 29ers great for most types of riding, and especially for fast, endurance rides. Beginners also benefit, because a 29er’s forgiving ride on rough surfaces makes it easier to learn to ride off road.
The disadvantages come from the sheer size of the wheels.
- Heavier: They’re unavoidably heavier, and any technological tweak that helps makes them lighter can also be applied to 26-inch wheels.
- Slower acceleration: The extra weight makes them slightly slower to accelerate than a 26er, in theory at least. In practice, on rough surfaces, it feels like the ride-smoothing effect swamps this.
- Poor handling: The ponderous handling of early 29ers was down to poor steering geometry. With your eyes closed, it’s now hard to tell a 29er from a 26er because bike designers have dusted off their textbooks and rediscovered the equations that determine good bike handling.
What about the little guys?
Diminutive riders might struggle to find 29ers that fit them well because the extra height of the wheel pushes the handlebars up. That also gives suspension designers problems as they try and design 29ers with more than about five inches of rear wheel travel.
To get round these two problems, an intermediate size has emerged.
Dubbed 27.5-inch, it’s based on a rim that’s in between the classic mountain bike 26-inch size and the 700C/29-inch size.
(If you want to delve deeply into the mess of systems and terminology that describes bike tyre sizes, Sheldon Brown’s website is a good place to start.)
27.5-inch mountain bikes give smaller riders and long-travel suspension bikes some of the faster-rolling advantages of 29ers, and look set to carve a niche for some applications.
Unless you’re into one of those niches, which generally involve riding down technical trails as fast as possible, a 29er is almost certainly the way to go if you’re buying a new bike.
For general mountain biking and especially for cross-country and endurance racing, they’ve proven themselves superior in both speed and user-friendliness.
29er Vs 26er. Which is Better?: Click on the link here to check out a quick head-to-head comparison test.