What Size BMX Bike Do I Need?

BMX bikes are built for freestyle riding or racing. Freestyle ones are designed to withstand any stress that comes with doing stunts on streets, skate parks, and dirt jumps. Basically, they have sturdier, thicker frames and tires for maneuverability. In comparison, race BMX bikes are constructed with lighter frames to boost their stability and speed.

BMX bikes are available in different frames based on age, size, weight, and rider’s height. Luckily, finding the right BMX bike is made easy by this guide. You will skip the hassle and bustle of visiting tons of bike shops or online stores.

The Right Size BMX Bike Matters

The size of your BMX bike will have a great impact on your riding experience in terms of control, pedaling efficiency, and overall bike performance. Considering that the sizes and measurements vary across manufacturers, you want a BMX bike with the perfect top tube length for comfortable riding with effortless maneuvering.

BMX bikes are available in multiple wheel sizes ranging between 12″ and 24″, with the most popular one being 20″, which features varying top tube lengths. Top tube length – the distance from the seat tube to the head tube – is the most important thing to consider when looking for the right BMX bike size.

In some cases, taller riders prefer bikes with a shorter top tube to make quick moves and attain a low-speed balance. Also, several shorter riders go for longer bikes which tend to be stable when riding at high speed and very effective when jumping raised trails.

Frame Size

Freestyle BMX bikes are mostly for kids, teenagers as well as adults who like stunts on the streets. Even though the wheel size for these bikes is almost the same, their frames can differ subtly to suit varying riding styles and heights of riders.

The factor most likely to tip the scale is comfort when picking the right BMX bike fit because different riders might like larger or smaller bikes.

Below is a breakdown of various BMX frame sizes based on rider’s height, weight, and top tube length. Some measurements overlap due to varying frames and in-between sizes of some riders.

 

 

 

 

Rider Height

(feet & inches)

Rider Height (cm)Rider Weight (pounds)Frame SizeTop Tube Length (inches)Top Tube Length (cm)
 

4’0″ and under

 

122

 

40 – 65

 

Micro-Mini

 

15″ – 16″

 

38 – 41

 

4’0″ – 4’6″

 

122 – 137

 

50 – 85

 

Mini

 

16″ – 17.5″

 

41 – 44

 

4’4″ – 4’10″

 

132 – 147

 

60 – 100

 

Junior

 

17.5″ – 18.5″

 

44 – 47

 

4’8″ – 5’4″

 

142 – 162

 

70 – 110

 

Expert

 

18.5″ – 20″

 

47 – 51

 

5’2″ – 5’8″

 

157 – 172

 

75 – 125

 

Expert XL

 

19″ – 20″

 

48 – 51

 

5’6″ – 5’10″

 

167 – 177

 

100 and over

 

Pro

 

20″ – 20.5″

 

51 – 52

 

5’10″ – 6’0″

 

177 – 182

 

140

 

Pro XL

 

20.5″ – 21″

 

52 – 53

 

6’0″ and over

 

182 and over

 

160

 

Pro XXL

 

21″ – 22″

 

53 – 56

 

Wheel Size

12″ Wheel Size

Getting your kid a new BMX bike is one of the best decisions to make, but picking the right size isn’t a walk in the park. BMX bikes with 12″ wheels are suitable for children between 1 to 4 years.

These bikes are created to improve balance and ensure the child’s feet touch the ground upon sitting on them. Be keen on the distance between the handlebars and the rider’s chest – the child should comfortably hold the handlebars while they are sitting on the bike for easy riding.

14″ Wheel Size

This class is designed to suit children with heights between 90 cm and 130 cm. They are made with sturdy alloy frames to substantially taller and heavier kids of about 5 to 9 years. 14″ wheel BMX bikes are a bit bigger, heavier, and durable than the 12″ wheel BMX bikes. Also, they are suitable for learning tricks and building confidence on giant ramps.

16″ Wheel Size

This class of wheel size is suitable for riders with heights between 100 cm and 140 cm. They come in Chromoly frames, sealed bearings, and regular 20″ BMX hubs. Even though building 16″ wheel BMX bikes from scratch can be expensive, many companies have started to offer exclusive brands at affordable prices.

18″ Wheel Size

BMX bikes with 18″ wheels are meant for bikers who can ride the 20″ BMX bikes but are limited by their height. Their quality, durability, and price are almost the same as the 20″ BMX bikes. Apart from being lightweight and versatile, these bikes best fit riders between 7 and 13 years.

20″ Wheel Size

Most BMX bikes come in 20″ wheel size, which is smaller than road bikes and mountain bike wheels. Also, a 20″ wheel size BMX bike can be ridden by adults of all sizes and shapes. It’s the most preferred and used BMX bike for racing trails or dirt jumping because it’s quite comfortable and offers more stability.

22″ and 24″ Wheel Size

This class has the most extended BMX bikes suitable for taller riders. BMX bikes with these wheel sizes are designed for cruising and tolerate regular trails or street abuse. Riders with 170 cm and above height are suitable for these wheel sizes.

Due to their longer and heavier frames, BMX bikes in this category are difficult to do tricks in the streets. Luckily, they are comfortable when it comes to commuting.

Riding Trails

Riding trails are the next thing to consider when picking the right size BMX bike. The most common trails for these bikes are the park, street, flatland, dirt jumping, and racing.

Street

Street riding involves riding on urban infrastructure like stairs and rails, where a rider showcases their creativity in performing tricks. Riders are always on the lookout for the best spots to try new skills. BMX bikes suitable for street riding are more rigid and better at tolerating grinding abuse and flat landings.

Park

Park riding is biking in skate parks, and it can extend to exclusive indoor parks for BMX riders only – they call them “ramps.” A more responsive BMX bike with a shorter top tube length, shorter chainstay, and steeper head tube is fit for park riding.

Flatland

The rider balances and pivots their bike on a flat surface in flatland riding. Here is where riders are free to try all sorts of riding tricks. Any kind of BMX bike is suitable for flatland riding as long as it’s light and has a strong frame.

Dirt jumping

Dirt jumping is riding on purpose-built dirt jumps and berms. Most riders prefer bigger and more stable BMX bikes that are comfortable to ride as well as jump larger trails.

Racing

BMX racing takes place on purpose-built courses made from hard-packed and well-groomed dirt and sometimes features undulating terrains and long jumps. Stable and robust BMX bikes suitable for racing have lightweight frames, longer top tube lengths, longer chainstays, slacker head tube angles, and larger front sprockets for high gear ratio, enabling bikers pedal at high speeds.

Tires

Tires are an essential part of a BMX bike as they control its speed, grip, and overall performance. Smooth-rolling and broader tires are suitable for street and park riding.

Contrary, the ones with more tread are best for dirt jumping as they offer more traction and better grip even when running at low pressure. Racing tires are narrow with slimmer rims and less weight for high speeds on the race tracks.

Pedals

The recommended pedals design for freestyle BMX bikes is wide-platformed plastic pedals. Besides their affordable design, plastic pedals are safer than metal ones should a blow on your shins occur.

Handlebars

BMX bike handlebars vary depending on the type of riding. For instance, freestyle handlebars are steeper than race bikes to ensure a firm grip and easy maneuvering.

Handlebars on 24″ BMX bikes may lack crossbars and have a lower rise to account for the higher stack length due to bigger wheels and larger frames. While flatland handlebars have a minimal sweep, they feel the same when pointed forward or backward. Also, these BMX bikes have a low crossbar to allow riders to swing their legs during creative riding.

Brakes

BMX bike brakes must be high quality with pure stopping power to offer better modulation prevent accidents. Most BMX bikes use rim brakes; that is, the pads push against the rims to reduce speed.

Freestyle bikes mainly incorporate U-brakes in both the front and rear. Many are equipped with a “gyro” braking system or a detangler to aid bar spins, allowing a 360 degrees spin without entanglement. For BMX racers, front breaks are not a must; mostly, they go for secure linear-pull rear brakes.

Rims

The recommended rim width for freestyle bikes is 32mm. Most BMX rims are made of aluminum and can be single, double, or tripled walled. Most riders opt for double-walled rims to balance their strength and weight while on the bike.

Advanced bikers prefer to have aftermarket-built wheels in order to suit their particular needs.

Spokes

Spoke count is another factor to consider when picking the right BMX bike fit. The strength and weight of the whole wheel are dependent on the number of spokes. Spokes are basically laced from the hub to the rim and are tension reliant to ensure optimal functioning and strength.

A freestyle BMX bike will function well with a 36 spokes wheel, while a 48 spokes wheel is fit for advanced or heavy riders. For race bikes, they mostly have 28 to 36 spoke wheels.

Hubs

Hubs are made of alloy and act as the centerpiece of the BMX bike wheel, housing the bearings that spin the wheel. Most suitable bikes are designed with sealed bearings to enhance a smoother and reliable ride. The recommended axle size for BMX bikes is 14mm, with flatland ones going for as low as 10 mm to save on weight.

There are four types of BMX bike hubs:

  • Cassette hubs – The cassette hubs are primarily used in racing and freestyle BMX bikes due to their lightweight and easier installation and maintenance.
  • Freecoaster – The freecoaster hubs are great for specific tricks and are only used by flatland riders. They have an internal clutch system that enables the wheel to drive backward without the cranks turning. Plus, they are more expensive and heavier than cassette hubs.
  • Freewheel – The Freewheel hubs were standard in BMX bikes before the cassette hubs takeover. The driver or sprocket in freewheel hubs is threaded on the hub shell, which tends to limit gearing options for freestyle riding.
  • Coaster – The Coaster hubs or ‘back pedal brakes’ engages the brakes for forward and backward pedaling. These types of hubs are used on kids and entry-level BMX bikes.

Gearing

Most BMX bikes do not have multiple gears; therefore, the most important thing to consider is the gear ratio. Gear ratio is the ratio of the number of teeth on the chainring (front) to the sprocket (rear).  A typical BMX gear ratio is 25/9.

Flatland and street BMX bikes prefer a smaller gear ratio to enable easy navigation during complex tricks and better clearance. For BMX race bikes, riders need to generate more power, requiring a larger chainring, but it might change depending on the race track demand.

Cranks

Cranks connect BMX bike pedals to the sprocket. They are available in different lengths (145 – 190 mm), shapes, and materials. The strongest and most durable cranks are made of Chromoly.

The majority of freestyle riders go for shorter cranks for better clearance when performing stunts on the streets. For BMX race riders, the crank is made of lightweight aluminum, and its lengths depend on the height of the rider.

Conclusion

BMX bikes are available in many shapes and sizes; thus it’s crucial to select the correct size that matches your height and the nature of the trails you will be riding on. Essentially, test-ride your BMX bike before buying as some look right but might feel different after riding.

Despite your riding trails, most complete BMX bikes have 20″ frame size or wheel size and are fairly built to function in almost all trails. It’s upon you to determine the right fit. Happy shopping!