Most mountain bikes today are offered in one of two wheel sizes: 27.5˝ (also know as 650b) or 29˝ (called 29ers), with traditional 26˝ wheels reserved for dirt jump, freeride and kids’ bikes. These widely used measurements refer to the tire’s diameter, and are typically paired with a tyre width in inches when written out, (i.e. 29 x 2.0, 27.5 x 2.4, 29 x 2.8). Here at Trek, we’ve been studying wheel size for nearly two decades alongside mountain bike legend Gary Fisher, and our breadth of experience has provided unique insights about the riding characteristics and best applications for each mountain bike wheel size. This guide provides a general introduction to the ride feel and characteristics of each wheel size that we offer to help you find the MTB that best fits the way you ride.
Cross country & Smart Wheel Size
Our years of research have told us that 29˝ wheels are the most efficient choice for most bikes and riders. However, we’ve also learned that pedalling efficiency and power output in the saddle depend on getting the right bike fit and positioning. While our trail bike line-up includes a wide variety of wheel and tyre options for all types of riders, we keep things simple with our cross country mountain bikes, using an approach called Smart Wheel Size. Each frame size is paired with the wheel that best fits the rider and sets them up for optimal efficiency and power transfer. We pair 29˝ wheels with 17.5˝ and larger bikes, and better-fitting 27.5˝ wheels for 15.5˝ and smaller bikes. Riders looking for the fastest and most efficient XC bikes will be ready to roll with Smart Wheel Size.
Trail bikes: the choice is yours
Many riders of full suspension trail bikes prioritise ride qualities other than efficiency, so our trail bike line-up offers a wide variety of wheel and tyre options. The primary consideration is whether you’ll appreciate the playful, precise feel of 27.5˝ wheels, or the speed and rollover capabilities of a 29er. In addition to the question of 27.5˝ vs. 29˝, there is now another variable to consider: plus-sized tyres. Plus tyres are 2.8˝ to 3.0˝ wide, offering even more traction and rollover capability and making them an excellent choice for beginners or those who prioritise grip over all else.
This size is best for those who favour manoeuvrability and want a snappy bike that they can easily get off the ground. It offers a more playful ride feel, quicker acceleration off the line and out of corners, nimbler handling for manoeuvring around obstacles, and is the best choice for smaller riders, downhill racers and many gravity riders.
This size is best for those who favour speed and rollover capability and want a versatile bike that’s great for a variety of rides. It offers more stability for increased confidence, more rubber on the ground for more traction, has better momentum and holds speed longer, rolls over obstacles more easily and is great choice for beginners, most trail rides and cross country or enduro racing.
Whether you choose to ride 27.5+ or 29+, these wider tyres (2.8-3.0˝ wide) are best for those who prioritise traction and stability. Their extra grip and forgiving ride make them perfect for those simply looking to have fun. They offer a super-plush ride thanks to their higher volume, extra traction for a more confident ride, more capability to ride in loose conditions or even snow, and ultimate rollover capability.