Mountain Bike Wheel Sizes: Which Option is Right for You?
Cycling expert Eli Schumont-Shipley breaks down the difference between the two most prevalent mountain bike wheel sizes so you can pick the one that's right for you.
Some of the most common questions I get as an expert here at Curated are about the different wheel sizes available on mountain bikes. People often wonder if 27.5-inch wheels (also called 650b wheels) or 29-inch wheels (often referred to as 29ers) would be a better choice for their new bike, or whether the bike they are looking at with one or the other will work for them. It can be a tough decision, and can be especially tricky if you are just getting back into mountain biking after a long absence (since the scene has changed drastically from even 15 years ago) or if you are new to the ongoing conversation. Wheel size can be a divisive topic in the mountain biking community.
It can be easy to get lost in the dialogue about stiffness, angle of attack, efficiency, and other complex-sounding topics. Luckily, the decision as well as the jargon, isn’t actually as complicated as it sounds. In the end, both a 27.5-inch wheel and a 29er will work well for most people (26-inch wheels have mostly gone obsolete, except with some downhill bikes), so the decision isn’t quite as scary as it may seem. That isn’t to say it isn’t an important decision, as the options let riders customize their bike to the terrain they ride and are important for getting an optimized bike.
Now, say you are looking at two beautiful new bikes, one with 27.5-inch wheels, the other with 29ers. Which one would be the best option? The answer depends on a few different factors which, when analyzed, will offer up the best choice for your purchase.
Key Factor: Height
The very first thing you should consider in terms of wheel size is your height. If you are under 5’6”, you will probably not feel comfortable on a 29-inch wheel bike. There are some options that will work, and 29-inch bikes can be custom designed to fit shorter riders, but generally the seat height to wheel size ratio puts shorter riders in an awkward riding position. This means that when buying an off-the-shelf bike, a shorter rider should err on the side of going with 27.5-inch wheels. By the same token, riders over six feet tall might feel more comfortable riding 29ers, as the larger wheel will accommodate their longer inseam better. A taller rider will have more leeway though, as 27.5-inch wheels will most likely still feel fine. To figure out if a specific bike might fit you, it’s often best to take it for a test ride, or to try to find reviews and discussions of other shorter or taller riders riding that specific bike, to see how other riders feel about it.
Height is the only strict factor in choosing a wheel size. The rest of the decision boils down to a series of preferences. Each size has its own benefits and disadvantages that fit different situations First, let’s discuss 27.5-inch wheels and why they might be the best size for some people.
Get to Know the 27-Inch
One of the best things about 27.5-inch wheels is that being smaller, they have less mass and are therefore lighter. It isn’t an insignificant amount either—bikes with 27.5-inch wheels usually end up being about two pounds lighter than their 29-inch counterpoints. Two pounds is a lot of weight to have to carry! This weight difference also means that 27.5s have better acceleration, because there is less weight to get moving from rest. This means that bikes with 27.5s are better when quick acceleration is required, and as in cross country racing, when every pound is paramount. If you want the lightest bike possible, you will want to go with 27.5s.
Another advantage is that 27.5s also tend to be more maneuverable than 29ers. This is partly due to the lighter weight, but also just comes down to having less wheel to swing around. It takes less effort to maneuver the front wheel of a 27.5-inch wheel bike, and they are also stiffer, adding to their responsiveness. This can be very helpful depending on the circumstance.
For example, imagine you are weaving your way through a series of tight turns on a trail set down in a valley of rock. 27.5s will be easier to weave through the tight squeeze and will be more responsive when it comes to making the quick turns. In the end, it will be far easier to maneuver the valley with smaller wheels. 27.5s are much better when it comes to tight spaces and rapid changes of direction.
Get to Know the 29er
Now for the other side of the coin—29-inch wheels. Whereas 27.5s are faster to accelerate, 29ers, being heavier, are better at holding momentum. This translates to an improved ability to ride over obstacles, to an easier time getting up hills (as the momentum will help carry you up the slope), and an overall ability to power through rough terrain. Forward momentum is extremely helpful in most aspects of mountain biking—from making it through technical sections, speeding up hills, and conserving energy. 29ers are often compared to monster trucks—they can make it over things much easier than smaller wheels can.
Still, the added weight of the bigger wheels might be a little worrying. While it is true that 27.5-inch bikes are lighter, even with being heavier, 29ers are more efficient over longer rides. This is because the bigger tires have to deform less, meaning less energy is sapped through deformation, and because larger wheels are better at overcoming resistance from small obstacles (even barely noticeable small rocks and such) which impede forward momentum. Therefore, if you are worried about the extra weight due to concerns over exhaustion, you probably won’t even notice a difference! This advantage increases with longer rides, when the greater efficiency will be more noticeable.
29-inch wheels also tend to be better when things get slippery. They have better traction than their smaller counterparts, because they have a greater contact patch (the area of wheel that touches the ground at once). More rubber against the ground means better grip. I notice the difference myself when cornering on dusty trails and feel much more stable and secure on 29ers. This is also due to the longer wheelbase 29ers offer, which means that though they are less maneuverable, they tend to feel more stable. The added traction and stability goes a long way for rider confidence.
Lastly, 29ers are much better at rolling over obstacles. This is due to a shallower angle of attack (the angle at which the surface of the tire meets an obstacle), and is very noticeable, even when riding over smaller roots and rocks. It takes less effort to get over everything—from logs to rocks to ledges and terrain features. This advantage is especially notable on technical sections. It is just much easier to keep going forwards, meaning those tricky sections will be easier to conquer. Rides also tend to feel much smoother, as 29ers won’t drop into ruts as much as smaller wheels will.
Say you are blasting down a dusty trail covered in lava rock, with many bumpy sections and ledges to get up and down. The increased rollover ability of 29ers will help to get over the rocky terrain, the stability will help to maintain balance on the drops, and the traction will help with cornering when it gets slippery. This same ride would be more difficult with 27.5s.
To sum it all up, 27.5s are better if you want a light, maneuverable bike with faster acceleration, and 29ers are better if you would prefer a more efficient, stabler bike that will be easier to get over obstacles, and that will have better traction. As we discussed, if you like to ride trails with quick turns and tight passageways, 27.5s will probably suit you better. If you prefer more technical, dusty trails with lots of obstacles, 29ers will make your rides go a lot smoother. In the end, remember that both sizes are still good options. Neither will be unrideable, and the decision just comes down to personal preference and riding style. Modern trail bikes are built to be very versatile, and that won’t change through just a few inches of wheel diameter. Think over the decision, and then make your order, so you can get to ripping!