September 15, 2023
In the beginning all mountain bikes came with 26” wheels. However, these days mountain bike wheels have gotten bigger. The underlying motivation is pretty simple, a larger wheel diameter rolls over obstacles easier than a smaller one. Imagine someone on a skateboard getting hung up on a sidewalk crack. This is an exaggerated example (skateboards have really small wheels!), but the concept is the same.
Today’s mountain bike wheels primarily come in 29”, 27.5” or a mix of both. Here are the highlights to help you decide which is right for you.
More Agile – Smaller wheels have a more playful feel with improved handling as they’re quicker to enter and exit corners. The lower center of gravity can also be helpful when riding steep descents.
Lighter – 27.5” wheels make for a lighter bike overall, plus less rotational weight makes for snappy accelerations.
Better for Shorter Riders (5’4” / 162cm and below) – Smaller wheels increase standover height and make it easier for the rider to move the bike around underneath them. Riders are also less likely to get “butt rub” from the rear wheel when leaning back on steep descents.
Attack Angle – Smaller diameter wheels get hung up in holes and rock ledges more easily.
Pedal Strike - This is also dependent on frame geometry, but in general 27.5” bikes have a lower bottom bracket which makes you more prone to pedal strikes.
Slower - Smaller diameter wheels are quicker to get up to speed but once there they’re less efficient than a larger wheel.
Attack Angle – Larger diameter wheels roll over the rough stuff easier and smooth out the ride.
Fewer Pedal Strikes – 29” wheels enable frame builders to find the sweet spot in bottom bracket height, balancing a low center of gravity for better handling with a high enough BB height to avoid pedal strikes.
Faster – Once up to speed a 29” wheel is more efficient than its 27.5” counterpart.
Less Playful – Think of how easily a BMX rider moves a 20” wheeled bike around underneath them. The larger the wheels and resulting bike gets, the harder it is to do that.
Heavier – Larger wheels increase the bike weight overall, but also add rotational weight which significantly slows down accelerations.
Not great for shorter riders. Increased standover height, handles like a larger bike, and smaller riders will often experience “butt rub” from the rear tire when leaning back on descents.
Also known as mullet, MX, and 295, a mixed wheel setup tries to take the best of both worlds.
Attack Angle – The 29” front wheel rolls over obstacles in the trail easier. Most of the benefit here is realized with the front wheel. Once your front wheel clears an obstacle the rear wheel (even if smaller) is likely to follow and not get hung up.
Playful Rear End – The smaller rear wheel is easier to move around beneath the rider. It also lowers your center of gravity which is helpful when descending in steep terrain.
Pedal Strike – Also depends on frame geometry but in my experience you get a lower BB and more pedal strike. Running shorter length crank arms can be an effective mitigation.
Less Efficient – Smaller wheels are less efficient once up to speed.
When I’m asked questions about wheel size I usually answer with something like — If you’re under 5’4” then go 27.5” front and rear. If you’re over 5’4” then pick based on what you want to optimize for – if you’re looking to ride jump lines, steep descents, and other gnarly trials, then go MX, otherwise 29” front and rear.
It’s also important to remember that we’re just geeking out here. Riding bikes is fun, regardless of wheel size. Run what you brung!
If you want to geek out further on the evolution of MTB wheel size trends, check out these charts!