What 650b is
650b is a wheel size with a 584 mm bead seat diameter. It is the same rim size usually sold as 27.5 inch in mountain biking. The name comes from an older French size system, where 650b was a traditional touring size. It has returned on gravel, touring and mountain bikes. If you want the background on naming, see bike tire sizes explained.
650b, 27.5 inch and 26 inch
- 650b and 27.5 inch: same 584 mm bead seat, so tires are interchangeable by diameter.
- 26 inch mountain: 559 mm, a smaller rim. They are not interchangeable.
- 650c: 571 mm and a different, older size. Do not confuse it with 650b.
650b vs 700c
A 650b wheel has a smaller rim than 700c (584 mm vs 622 mm). With a wider tire, the overall diameter of a 650b wheel can end up close to a narrower 700c wheel. Commonly cited benefits of 650b are room for a wider, higher-volume tire on the same frame, which may improve comfort and grip on rough or loose surfaces. 700c is usually considered a good fit for smoother surfaces and has the widest tire selection. Testing on comfort, such as work by CyclingAbout, suggests tire width and pressure matter at least as much as wheel diameter, so wheel size alone is not a guarantee of comfort. See also what 700c means.
Why gravel and touring bikes use 650b
Gravel and adventure frames often use 650b so they can take wide tires, often in the 40 to 50 mm range, with mud and suspension clearance, while keeping a similar overall wheel height to a 700c setup. Smaller frame sizes may also use 650b so that toe overlap and handling stay reasonable. Some bikes accept both sizes, so check the frame specifications.
Can 650b go on a 26 inch or 700c bike?
- On a 26 inch frame: Sometimes. The 650b wheel is a bit larger, so you need clearance in the frame and fork, and brakes may need checking. Many manufacturers do not approve it.
- On a 700c frame: Often possible, because 650b is smaller, but rim brakes may need longer-reach calipers and the bottom bracket gets lower. Disc brakes are simpler. Changing wheel size also changes handling and geometry, so confirm with the frame maker or a bike shop.
- Can you use 650b tires on 700c rims? No. The bead seat diameters differ, so the tire will not fit.
Choosing widths
Typical 650b widths range from around 38 mm for gravel to 2.2 to 2.5 inches for mountain-style tires. Your frame, rim and fork limit your maximum. To see how to check your current size first, read how to find and measure your bike tire size.
Is 650b right for you?
Choose 650b if you want wider tires, ride rough or loose terrain, or ride a frame designed for it. Stay with 700c if your frame is built for it and you ride mostly smooth roads. You can look up neighboring sizes in the bike tire size chart.