Condensed Answer: BMX bikes rely on small (20-22″) wheels for extra strength, maneuverability, acceleration, and nimbleness.
The Advantages of Smaller Wheels
When all parameters are equal (e.g., materials, construction quality, architecture…etc.), smaller wheels are stronger than larger ones and can face greater impact without deforming.
The shorter radius of smaller wheels makes them more robust by reducing the leverage that can be used against them. Hence why it’s easier to bend a 29″ wheel than a 20″.
Additionally, smaller wheels are stiffer because the spokes are shorter and less springy. This is beneficial in the world of BMX because the wheels offer fast and direct feedback.
Smaller wheels are easier to turn. Consequently, BMX bikes are a lot more maneuverable than full-blow MTBs, for example.
- Supreme Acceleration
Smaller wheels are easier to get to a high RPM (rotations per minute) thanks to their smaller circumference and lower weight.
This quality is beneficial in the world of BMX because riders often have very little room for accelerating before a trick.
- Small Frames and Forks
Larger wheels will require a larger frame and fork which will make the bike heavier and more difficult to throw around.
Part of the reason why BMX bikes are so small lies in their origin. BMX stands for bicycle motocross or bike motocross and goes back to the 1970s when children began riding their bicycles on dirt tracks in southern California, trying to imitate the motocross stars of the time.
Since BMX bikes were designed for youngsters imitating motorcross riders, the frames and wheels had to be small.
Eventually, people realized that BMX bikes excel at the performance of stunts as they were and saw no reason to make the bikes larger and more adult-friendly.
The Disadvantages of Small Wheels
Smaller wheels accelerate faster than larger ones but have a harder time reaching high speeds and maintaining them.
If two bikes have the same gearing but wheels of different sizes, then the bike with the larger wheels can reach higher speeds via pedaling because each rotation of the rear wheel equals a greater travel distance.
For example, if the gear ratio is 4:1, the rear cog and respectively the rear wheel would make 4 rotations per 1 spin of the cranks. If the rider is making 60 rotations per minute, the rear wheel will turn 240 times in that time frame. The bike with the larger tires will be faster because they have a greater circumference and thus propel the bike over a greater distance.
However, freestyle BMX bikes are designed for tricks rather than speed. Of course, there are also racing BMX bikes but they compete against other units of the same genre rather than bikes with larger tires. Thus, the smaller wheel size is not a limiting factor.
2. Not ideal for off-road
Smaller wheels have a harder time overcoming road irregularities. Consequently, BMX bikes are not the best performer on MTB trails.
3. Not Ideal For Tall People
If you’re on the tall side (6’2″ +), a BMX could feel a little claustrophobic. In that case, you can try going for a 22″ BMX or maybe even a dirt jumper.
That said, plenty of tall people are freestyling with standard BMX bikes with 20″ wheels and fairly short top tubes. After all, BMX bikes are not designed for comfort. Their primary purpose are tricks and racing against other BMX machines.
If you want comfort, then a commuter or an MTB will serve you better.
Not All BMX Bikes Are Small
Standard BMX bikes use 20″ wheels, but there are also 22″, 24″, and 26″ models. Those units are better for taller riders who feel too “compressed” on regular BMXs.
The downsides of bigger wheels are the extra weight and the larger profile of the bike which make trick execution more difficult. For that reason, it’s recommended to stick with 20″ or 22″ wheels if the bike is going to be used for tricks rather than just commuting.
FAQ: Can I install larger wheels on my BMX?
Not really. The current frame and fork won’t offer enough clearance for the new wheels. If you need a bigger BMX bike, you will have to purchase an entirely new unit. Another option would be to go for a dirt jumper since the basic versions come with 26″ tires.
Summary: What You Need To Know
The primary reasons why BMX bikes use small wheels are:
- BMX originated as a kid’s sport. The bikes were used by children to ride on motocross tracks.
- BMX bikes have fairly small forks and frames that cannot accommodate larger wheels. The small bikes make the execution of difficult tricks easier because the bikes are lighter and smaller in comparison to the rider.
- Small wheels are more maneuverable, stronger and accelerate faster.
- If the user wants larger wheels, the other options are 22″, 24″ and 26″. The downside of going up in wheel size is the extra difficulty when performing tricks. Also, the available large models are quite limited in comparison to the standard BMX size.