Common fat bike wheel sizes
Fat bikes use wide tires, usually about 3.8 to 5 inches, on wide rims. Typical sizes are:
- 26 x 4.0 and wider (for example 26 x 4.8): the most common size, built on a 559 mm bead seat diameter.
- 20 x 4.0: common on smaller fat bikes and many fat e-bikes.
- Larger diameters: some bikes use 27.5” or 29” wheels with wide tires, though these are less common.
Availability varies by brand, so check your bike’s specifications.
What the numbers mean
In 26 x 4.0, the first number is the approximate overall tire diameter in inches and the second is the tire width in inches. The measure that really determines fit is the bead seat diameter, printed as the ISO/ETRTO number. The bike wheel size conversion guide explains how to read it. On many fat bikes the 26” size uses 559 mm, but confirm on your tire.
Rim width and tire width
Fat bike rims are much wider than standard ones, commonly somewhere between about 65 mm and 100 mm. A wider rim suits a wider tire, so check the tire maker’s recommended rim width range; the fat bike tire sizes chart lists common combinations. Rim width also affects the tire shape and the clearance needed in the frame and fork.
20x4 vs 26x4
A 20 x 4.0 tire has a smaller rim and overall diameter than 26 x 4.0. In general:
- 20” wheels are more compact and can suit smaller riders or bikes designed around them.
- 26” wheels are taller and usually roll over obstacles more easily.
Tire options for each differ, so check the choices available for your size.
Can you swap between sizes?
The two sizes use different rim diameters, so a 20x4 tire will not fit a 26” rim. Switching means new wheels, and the frame and fork must have room for a larger wheel. Brakes, mounts and geometry are also affected, as described in can you change the wheel size on a bike. A tire change within the same rim size is much simpler, provided the tire width suits the rim and frame.
Riding in snow
Yes, fat bikes are designed for snow and sand, because the wide tires spread the rider’s weight and run at low pressure. How well they work depends on snow conditions, tire choice and pressure. Some riders use studded tires on ice.
Pressure and care
Fat bike tires typically run at much lower pressure than other bikes, so a low-pressure gauge is useful (see the fat bike tire pressure guide). Ideal pressure depends on rider weight, tire, rim width and terrain, so start with the tire maker’s guidance and adjust gradually. Check regularly, as small pressure changes make a large difference at low pressures.
Finding your size
- Read the sidewall marking on your tire.
- Note the rim width if it is printed on the rim or listed in the specifications.
- Measure frame and fork clearance before choosing wider tires.
622 vs 700c
Yes, 622 mm and 700c refer to the same rim size. Fat bikes rarely use it, since most are built on 559 mm rims.