A mountain bike on the bike rack of a car with trees and a cloudy overlook in the background.

Early on, mountain bikes came with 26˝ wheels. Then Gary Fisher came along and made 29-inch wheels that quickly became popular thanks to their momentum-preserving speed. Since then, 26˝ mountain bike wheels have been replaced by 27.5˝ wheels that deliver some of the benefits of 29ers while offering more nimble handling and a better fit for smaller riders.

Mountain bike wheel sizing

26-inch wheels

The original mountain bike wheel size is now the least common. Since these are the smallest and most nimble mountain bike wheels, they are still used on dirt jump and slopestyle bikes that are made for doing bmx-style tricks in the air.

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27.5-inch wheels

The better small wheel. This size is faster and rolls over obstacles a lot easier than a 26˝ MTB wheel, but it’s still more nimble than a bigger 29er wheel. This wheel size is a great choice for smaller riders, downhill mountain biking, and some trail riders who prefer to pop off jumps and throw the bike around on the trail.

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29-inch wheels

Why 29er mountain bikes? The bigger diameter gives 29˝ wheels the advantage of speed. They also roll over obstacles easier. But when comparing 27.5 vs 29, these bigger wheels take more effort to control. Since these are the fastest-rolling wheels, they’re the best choice for cross country mountain bike racing. Their speed and momentum also makes them great for enduro mountain bikes and general trail riding.

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Smart Wheel Size

While 29-inch wheels are generally the fastest, they can be more difficult for smaller riders to control. That’s why Trek offers our most popular bikes with Smart Wheel Size. We pair each frame size with the wheel size that best fits that size rider. That means larger frame sizes get 29-inch wheels while the smallest sizes get more proportional 27.5-inch wheels, and everyone gets the fastest wheel that fits.

Mountain bike tire sizing

Mountain bike tire width recommendations usually depend on riding type, and sometimes riding conditions.

Cross country bikes

Since cross country riders are all about speed and efficiency, they want the lightest, fastest-rolling tires, and they are often willing to sacrifice some grip and stability to save weight. So XC bikes usually have narrower tires with smaller tread.

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Fat tire mountain bikes

These bikes have the widest tires that give you tank-like traction and rock-solid stability so you can steamroll over loose terrain and go where other bikes can’t. Fat tire bikes aren't quite as quick or nimble as trail bikes, but they give you the best in all-season, all-terrain capability and grip.

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A mountain biker turns a corner on a narrow path lined with tall grass and flowers with trees and mountains in the distance.
The lit storefront of a Trek bike shop at dusk.