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Why do BMX bikes have small cranks?

Author

Emily Cortez

Published Mar 01, 2026

Why do BMX bikes have small cranks?

Many BMX bikes use a U-style rear brake mounted to the top of the frame chain stay. With this style of brake mount, a very small sprocket and rear cog will lower the chain so much it contacts the top of the brake and inhibits pedaling. Typically the smallest gear combination a bike of this style will allow is a 36/13.

People also ask, why do some bikes have small cranks?

“Ironman athletes are running shorter cranks — down to 155mm, in some cases — to help maintain a healthy hip angle as they rotate their bodies around the bottom bracket,†said Morton. “They can move forward and lower the front end of the bike and still make a good transition off the bike for the run.â€

Similarly, why are BMX bikes so tiny? According to New York bike shop Bicycle Habitat's website, the bikes themselves are typically made out of chromoly steel or aluminum. Aluminum frames are lighter and they're also rustproof. According to Mpora, BMX racing developed from a love of riding fast, so small bikes have always been a part of the sport.

Likewise, people ask, what size cranks should I use BMX?

Most riders these days run a 170mm or 175mm size, but you could go shorter or longer (Shorter is more ideal for street and flatland riding and longer is more ideal for jumping and racing). That 170mm – 175mm size is pretty ideal for street, park and dirt riding.

Are BMX bikes supposed to be small?

The 'standard' size for a BMX wheel is 20in, which is much smaller than a mountain bike or road bike. Even smaller 16in or 18in wheels can be found on kids bikes, and a larger 22in or 24in wheel can be seen on some 'trail' BMX bikes used for dirt jumping.

Should I go for shorter cranks?

A shorter crank length for the shorter triathlete will give all the above benefits and more, as less leverage will encourage a higher cadence saving their legs for the run. A lower aero bar position is achievable as knee tracking at the top of the stroke is improved.

Are longer or shorter cranks better?

Crank length changes may help solve long-simmering aches and pains, but they're most effective when you're doing everything you should be doing to be strong on the bike. It changes gearing. If you do end up changing crankarm lengths, it will change your gearing as well.

Does bike crank length matter?

Crank length simply didn't matter. So what's the bottom line? According to Martin, “Cyclists can ride the crank length they prefer, without limiting power.†So the crank length that came on your bike is just fine. And you don't need special cranks for time trials, sprinting or climbing.

What is the difference between 170mm and 175mm cranks?

Whereas now 170 is 'short' 172.5mm is 'normal' and 175 mm cranks are very common. Still though, the difference between 170 mm and 175mm is less than 3% and leg lengths of bike riders vary by far more than that.

What size cranks do pros use?

Pros often use a 55×11-tooth high gear for time trials. On flat or rolling stages they might have 53/39T chainrings with an 11-21T cassette. In moderate mountains they switch to a large cog of 23T or 25T. These days, they've joined the big-gear revolution like many recreational riders.

How do I know my crank length?

Crank length is measured from the centre of the bottom bracket axle to the centre of the pedal axle. If you're not sure what length the cranks on your bike are, the quickest way of finding out is typically to just look at the backside of your cranks, just below the pedal axle.

Are all bike cranks the same size?

The crank length represents the distance between the centre of the bottom bracket and the centre of the pedal axis. The most common lengths are 170, 172.5 and 175 mm, but it is possible to find cranks between 165 and 180 mm in the market.

Are all BMX spindles the same length?

Not only do BMX cranks come in multiple lengths, but they also come in three different spindle sizes; 19mm, 22mm and 24mm.

What do you need for BMX?

Safety gear is required for all riders
  • Full Faced Helmet. A “full face†helmet is needed for BMX racing.
  • Full Fingered Gloves. A pair of gloves must be worn on your hands.
  • Long Sleeved Top. A long sleeved top worn tucked in, is required.
  • Long Pants. Long pants must be worn, not ¾ pants or long shorts.
  • Socks.
  • Closed Toe Shoes.

What is a 2 piece crank?

2 piece cranks consist of two distinct parts – a “free†crank arm plus a crank arm with a spindle/axle attached to it.

What is a crank on a BMX?

BMX cranks are the metal arms that connect bike pedals to the bottom bracket. Compared to race BMX bike cranks which are made out of aluminium or carbon fibre, freestyle cranks are made from steel or Chromoly.

What is a BMX bottom bracket?

A Bottom Bracket is the bearing system within your bike that connects the cranks to the frame. Most BMX bikes currently have a MID Bottom Bracket, this represents the size of the bearing required to fit into your frame.

Is BMX bad for knees?

Research shows that more than 40 percent of recreational riders experience knee pain from overuse at some point or another. So—is cycling bad for your knees? The short answer is no; cycling is great for your overall health and easy on your joints.

Why are BMX bikes so expensive?

Well, BMX is so expensive because of the following three primary reasons: Lightweight (BMX bikes are the best bikes for stunt riding). Stronger (BMX bikes are adaptable to the rough usage on the streets or skate parks). Responsive (a BMX bike motivates you to go over the edge and further).

Is it bad to ride BMX in the rain?

Conclusion. There is nothing wrong with riding your BMX bike in the rain, if you're into BMX dirt racing you don't even have a choice. Just make sure to inspect your parts before you shred and clean your BMX when you're done. Just as MTB trail riders don't care about a little mud, neither should you.

Can you sit down on a BMX bike?

Original BMX bikes were designed for BMX racing, where you don't actually sit on the seat.

What does BMX stand for?

BMX is an acronym for Bicycle Motocross. A BMX bike is made for off-road racing and trick riding. BMX originated in California in the 1970s. Inspired by motocross riders of the time, people started to race their bikes on dirt tracks.

Are BMX bikes smaller than mountain bikes?

BMX wheel sizes are much smaller than those of mountain bikes. BMX wheel sizes range from 12′ to 24″ but 20′ is the most popular. 27.7″ and 29″ are the most common wheel sizes for mountain bikes; however, there are still 26″ wheel sizes available on some mountain bike models and brands.

Why do BMX bikes have saddles?

BMX seats point up to improve the riders' control of the bike when performing tricks and in racing, using it to pivot and lever the bikes over jumps and through the air. Having a pointed up saddle is also for comfort as it gives riders more clearance when pedaling.

Does BMX build muscle?

BMX is a great exercise for your body and your mind. It boosts weight loss, builds muscle, improves heart and brain health, and helps with posture. It also provides several mental benefits, such as reducing stress, improving sleep, boosting the immune system, and stimulating creative thinking.

What age is a 18 inch BMX bike for?

The next and last size is the 18 inch model for kids aged 8-11 years with body sizes up to 1.20 meters. Of course there are also differences in terms of facilities. The prices are to be distinguished from a normal 20-inch model hardly, unless you take out huge concessions in terms of features.

Is a 20-inch BMX bike for adults?

Adults can definitely ride 20-inch BMX bikes, but it is recommended that they wear appropriate safety gear to keep themselves safe. This type of bike can be more difficult for adults than other types of bikes because the smaller wheels require a lot more balance and coordination in order to ride safely.

Why are BMX seats so low?

Low seats provide clearance for more acrobatic body movements. This is essential for bunny hops and nearly every other trick which builds off of this skill. If you look at trials bikes they similarly have lots of clearance for the rider over the frame and the saddle.

Can a 6 foot person ride a 20 inch bike?

Mountain bikes use standard measurement, and a 6-foot tall man will fall somewhere between 18 and 20 inches, depending on your inseam measurement. If you're between sizes, it's best to size up, since you can make up the differences with a higher seat and longer stem.

Can adults ride 24 inch BMX bikes?

A 24-inch bike is designed for growing kids of age 8-13 years. It is best fitted for a height range of 4'1″-4'9″ or 135-145 cm. An adult or in most cases a female rider with the above-mentioned height limit can ride this bike size. They can ride the bike easily if it is designed according to their requirements.

What age is a 20 inch BMX bike for?

20" wheel BMX bikes are ridden by children and adults of all sizes but the minimum age for this style of bike would be between 7 and 8 years. Mountain Bikes: Standing flatfooted on the ground; you should have a minimum of 3" clearance between yourself and the top tube(cross bar) of the frame.

What age is a 22 inch BMX bike for?

Kids Bike Size Chart – Inseam Length
AgeInseamWheel Size
4–5 years old18–22" (45–55 cm)16" (41 cm)
5–8 years old22–25" (55–63 cm)20" (51 cm)
8–11 years old24–28" (60–72 cm)24" (61 cm)
11+ years old26'+ (70+ cm)26" (66 cm)

Are all BMX bikes 20 inch?

They usually have 20-inch wheels (24-inch-wheel "cruisers" are the exception), knobby tires, upright handlebars with crossbars, small saddles, long cranks and rear hand brakes. The frames are light and sturdy, and the higher the price, the lighter these bikes get. BMX bikes also come in different frame sizes.

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