If you road cycle it’s easy, but if mountain bikes are your ride of choice then things aren’t quite so simple. You’ve seen the bikes, you’ve heard the chat, but you still don’t really know which wheel size is right for you. From the classic 26”, to the rangy 29” to the new ‘tweener’ 27.5” (650b) wheels, modern mountain bikes come in a range of sizes to suit different riding styles and terrain.

The 26” wheel is the classic and has been around since the inception of the modern mountain bike. It might have become an accidental standard based on old beach cruisers (read about the history of the MTB here), but it still has a lot going for it.

• Lighter weight over other wheel sizes thanks to smaller diameter rims and shorter spokes. This gives the bike a more agile feeling with faster acceleration on smooth surfaces
• 26” wheels can be made stiffer and stronger, a reason why a number of top downhill riders still run this smaller wheel size
• Loads of existing 26in wheels, tyres, forks and bikes make spares cheap and easy to find
• Virtually all advancements in mountain bike geometry and technology have been modeled off of a 26” wheel which means that its front-center/rear-center balance is ideal
• Because they hit obstacles at a steeper angle and drop into holes easier they tend to stall and lose speed more rapidly than bigger wheels over rough terrain

The 650b wheel has actually been around for a number of years, initially used by boutique brands and on some touring bikes, it’s not until recently that have we seen industry leaders adopt the wheel size. In many cases now, companies are dropping their 26″ wheeled bikes in favor of the 650b size.

• Maintains speed, is smoother and offers better stability over rough terrain than 26” wheels
• Larger tyre to ground contact area gives more traction than 26” footprint
• Allows more maneuverability than a 29” wheel
• A 27.5” wheel doesn’t run into the same design challenges as a 29” wheel does, allowing the use of these wheels on more traditional geometries, and allowing the use of longer travel suspension than on a 29er
• Better size and fit for shorter people or woman than a 29er, but still achieving some of the advantages a larger wheel brings

The wheel that initially broke the stranglehold of 26” produces a very different feel. Once snubbed due to poor ride characteristics from outdated geometry, now days there’s a full range of 29ers to choose from, although most are still focused on the cross country and trail categories.

• Crucially, because they’re not as quick to get going and their smoothness dulls the sensation of speed they often feel much slower than they actually are.
• Once rolling though 29er tyres hit rocks and roots at a shallower angle and with more momentum so they roll over the top easier.
• The longer contact patch means any given tyre grips better or you can run slicker, speedier rubber without slipping.
• Smoother, grippier and more stable for better control on rough terrain
• Slower to get moving but hold their speed better once rolling
• Feel awkward on tighter, slower trails and harder to sync with long suspension or short riders
• Because of their size and stability, they’re still harder to hustle on really tight and twisty terrain than smaller wheels

The graphic above illustrates the difference between the 3 wheel sizes. It should be noted that the 26″, 27.5″ and 29″ names aren’t actually true to their actual measurements, and in truth the 27.5/650b is not even half way between the 26″ & 29″, it’s actually less than half way. It’s all quite confusing but the bottom line is the 29″ wheel is much larger than the 26″, and the 27.5″ is somewhere between the two.

While all wheel size options offer pros and cons at the end of the day, as long as you’ve got two of them underneath you, you’re going to have fun so get out there and ride!