Road & Gravel
By far the most popular wheel size on road bikes, 700c are the default wheels for pretty much every adult road bike. Still, you can find different rim widths and rim depths depending on ride variances. More narrow rims are more popular on race bikes where speed and aerodynamics are at a premium. As riding styles turn more casual or even venture off the pavement and onto dirt trails and gravel roads, rim width often gets a little fatter in order to accommodate tires with more traction and handling ability.
Once fairly common on smaller road bikes but diminishing in popularity, 650b wheels and tires are making a comeback thanks to the emergence of gravel riding. The smaller wheel size results in two primary things - more tire clearance as the rim sits a centimeter or so closer to the hubs and therefore better handling for more rugged dirt and gravel riding. These wheels are common on bikepacking rigs as well as many commuter or comfort bikes where speed is less important than the ability to safely maneuver around trails and obstacles. 650b wheels are the same diameter as 27.5 inch wheels, but are more road/gravel oriented and almost always have a narrower rim width.
On very small road bikes, such as those you might find ridden by junior rider learning to race on the road with the big kids, you’ll find 24 inch wheels that simply fit itsy-bitsy bikes better.
Now the most common size on the mountain, 29 inch wheels are a relatively new development in the genre. But once 29 inch wheels became a thing, they became THE thing. Offering more speed and smoother rolling over obstacles, 29 inch wheels are most popular on cross country and lower travel trail bikes. Still, you’ll increasingly find them on downhill and enduro bikes as technology and bike geometry adapt to the larger wheels. In most cases, 29 inch wheels improve a bike’s ground clearance and reduce impacts on the bottom bracket during rougher rides. 29 inch wheels also offer different widths to give riders options for more or less robust tires with different tread profiles.
For years, the 27.5 inch wheel was the standard on the mountain. And even though 29ers are popular, there remains a devoted class of mountain bikers who prefer the old-fashioned 27.5 inch wheel. The reason for this is usually related to bike handling and the ability to pick your way through rougher terrain instead of just trying to roll over it. Many bike brands still make models specifically for 27.5 inch wheels. Additional benefits of 27.5 wheels are less weight and usually a more stiff rim.
One wheel preference is a mixed build - often called a mullet build - where riders use a 29 inch wheel in front and a 27.5 inch wheel in back. It’s a matter of rider preference, of course, as some riders like the responsiveness of a 27.5 inch wheel in back and the obstacle clearance the 29 inch front wheel offers.
These wheels used to be virtually the only wheels on mountain bikes. They were everywhere. Slowly, they became less popular as 27.5 and 29 inch wheels took over the market. Still, you’ll find 26 inch wheels on older bikes as well as bikes for youngsters. BMX bikes also frequently use 26 inch wheels for their quick response under demanding conditions. In more rugged terrain, 26 inch wheels might sometimes get too deep into holes and rock gardens for your taste and require significant effort to ride through the rough stuff. One real drawback to riding 26 inch wheels is it’s becoming hard to find parts and tires for the wheels at many bike shops.
A relatively new entry to the cycling market are Fat Bikes. Ridden on snow or sand - or just around town for some people - Fat Bikes have gigantic tire widths to prevent the wheels from digging too deeply into the soft surfaces of snowy roads or sandy beaches. Accordingly, the rims are much wider than other bikes. With tire widths up to six inches to help keep you afloat on powder trails, the rims and wheels don’t need to be as large and you’ll usually find 26 inch wheels and occasionally 27.5 inch wheels on fat bikes. Tires are pretty hefty in profile and roll with lower tires pressure in order to stay supple and responsive to the road or trail surface.
Small kids ride small bikes and small bikes have small wheels. Makes sense, right? Depending on the age and/or size of the young cyclist in your life, you’ll find wheels ranging from 10 inches on balance bikes to 24 inches on bikes for tweenagers who like to ride bigger hills or to and from school. In addition to just fitting the bike and rider size more appropriately, smaller wheels typically have more puncture resistant tires and are more stable as small riders learn balance and bike handling skills. On many youth bikes, you’ll see wheel size grow a couple of inches for each year the child grows until they’re riding 20 inch wheels for a couple of years and then transitioning to 24 inch wheels which are almost like the grownups ride.