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Buying a BMX Bike: The Ultimate Guide

November 01, 2017
Buying a BMX Bike: The Ultimate Guide

BMX stands for ‘Bicycle Motocross’ so it should come as little surprise that BMX bikes themselves are best known for being piloted over jumps and ripping around berms, much like their petrol-powered cousins.

BMX originated in the early 1970’s when kids would mimic motocross races on their bicycles, complete with a number fastened to the front of the bike. They would take to dirt ‘tracks’ and race each other in a similar fashion to their motocross idols.

As expected, the racing got more competitive, the demands on equipment became higher and more specialised, and subcultures naturally formed around street and freestyle BMX.

Fast forward to today and BMX has come completely of its own, with BMX racing being UCI (Union Cycliste Internationale, the governing body of cycling), sanctioned and featured in the Olympic Games. Freestyle BMX has professional riders and teams supported by huge sponsorship competing at adrenalin-fueled events such as the X-games.

Feeling spoilt for choice with what BMX to buy? We are here to clear things up, spell out the differences and arm you with the knowledge to confidently purchase the right BMX bike to suit your needs.

BMX Riding disciplines

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Freestyle BMX bikes are designed to withstand the stresses that come with performing stunts on street features, dirt jumps, and skate parks. This means that the frame materials, wheels, and components must be equally optimised for both strength and ease of maneuverability. Race BMX bikes are optimised for speed and acceleration, so are often made from lighter materials and feature different geometry to ensure they are stable, stiff and nimble at speed.

Within freestyle BMX there are several sub-disciplines that fall under the umbrella of the term ‘freestyle’. With the exception of flatland, there is a lot of crossover within these disciplines, so choosing an all-rounder bike that is categorised as freestyle will likely be the most versatile option.

  • Park: Park riding refers to riding in skate parks, which despite the name, are frequented by BMX riders almost as often as skaters. Park riding also extends to BMX specific indoor parks for riders only, which are commonly referred to as ‘ramps’.

  • Street: As the name would suggest, street riders get creative with urban infrastructure such as stairs and rails to perform highly skilled tricks and turns. Riders will always be on the lookout for good ‘spots’ to try new tricks.

  • Flatland: Quite a niche style, flatland occurs with no external features and all the tricks are done with the bike by the rider. Often described as ‘breakdancing’ on the bike, riders pivot and balance the bike with on a hard flat surface.

  • Trails/Dirt Jumping: Occurs on purpose build dirt jumps and berms. These riders look at getting big air and linking up jumps in to perform tricks.

  • Race: BMX racing occurs on purpose built courses which are made from hard-packed, well-groomed dirt or bitumen and often feature a mixture of undulating terrain and long jumps. Because BMX race bikes are designed with a sole purpose in mind, they are often unsuitable for use in other BMX riding disciplines.

Frames and Fork

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Materials

Freestyle and entry-level race BMX bikes are predominately made from a steel composition known as Chromoly 4130 (chromo for short). Chromo is an alloyed steel which offers superior strength properties when compared to cheaper, ‘Hi-tensile’ steels typically found on lower end and department store bikes. Chromo steel is able to be ‘butted’, meaning it can be made to be thinner and therefore lighter in the middle of the tubing, and reinforced around the ends and joins for strength.

Steel is the material of choice for these bikes as it is highly resistant to fatigue (important considering all the hits these bikes take!), is easy to repair and offers some additional compliance to the ride which adds a little more comfort and reduces pressure on the body of the rider.

For BMX racing, the preference is for stiffer, lightweight frames meaning aluminium is the material of choice. If you are serious about your racing and want to get the extra edge, carbon fibre frames are growing in popularity amongst elite BMX racers as it reduces weight even further and has vibration dampening properties not found in aluminium.

For more information on bike frame materials, check out our comprehensive guide.

Sizing

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Freestyle BMX bikes are ridden by kids, teenagers and adults alike; therefore, although the wheel size stays consistent, the frame size can change subtly to suit the riding style and height of the rider. Most freestyle BMX bikes off the shop floor will come with a 21in top tube so that riders have enough room to swing the bike underneath them if performing airborne tricks, as well as a shorter seat stay which is easier to whip around.

Flatland frames are typically the only exception to this as they tend to be lighter and have shorter tubing all round for better balance and control. They also have a much steeper head angle and 3/8" dropouts for smaller rear axles.

On race bikes, slacker head angle and longer wheelbase put the rider further back on the bike, which allows for improved stability and handling at speed. Race frame sizes come in a wider range to suit the rider age spread that BMX racing sees.

Wheels

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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. However, it is safe to assume that ‘BMX’ will generally refer to a bike with 20in wheels.

Racing BMX bikes fall into two categories, depending on wheel size. The first is 20in - the most common, the second is 24in or ‘cruiser’. Cruiser bikes are popular amongst taller or older riders, and also offer more stability.

Because racing BMX demands lightening-quick acceleration out of starting gates, the wheels are lighter than in freestyle BMX.

Rims

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The standard rim width is 32mm for freestyle bikes. For those riders who expect they will put a few more hard-hits into the wheels, can opt for a wider 36mm rim. Rims are made of aluminium and can be single, double or triple walled, the more layers of metal provide more structural support, albeit at the penalty of increased weight. The ideal standard for a majority of riders is double wall as it is a good balance of strength and weight.

Advanced riders who put more demand on their equipment will generally choose to have wheels built up aftermarket to suit their requirements specifically and be more selective with rims and spoke count.

Spokes

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Spoke count is another thing to consider when choosing a BMX or buying some new wheels. Spokes are ‘laced’ from the hub to the rim and rely on tension to stay true and strong. The number of spokes contributes to the strength ( as well as the weight) of the complete wheel. A 36 spoke wheel will suffice for most riders on a freestyle BMX bike. More advanced riders or heavier riders may opt for up a 48 spoke wheel. Most spokes are made from a steel wire and are the same thickness all the way through, but if you see something referring to ‘butted’ spokes, like butted frames, this means that the spokes are thinner in the middle and thicker at the end for added strength but reduced weight.

Race BMX wheels will be anywhere between a 28 to 36 spoke build and have alloy rims engineered to shave weight where possible.

Tyres

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Being the first point of contact to the riding surface, tyre choice will affect the speed (rolling resistance), grip and handling of the bike. For street and park riding, smooth rolling, wider tyres are preferable. Premium BMX tyres can accept pressure of up to 110psi, which will roll faster than a lower inflated tyre and offer rim protection when under load after hard landings.

Dirt jumpers will opt for something with more tread for traction on the dirt and run their tyres at a lower pressure for better grip. Wider than a race tyre, look for 20in x 2.1 for better stability and more surface area. The good thing is, tyres are easily swapped and changed, so you can choose to change them if you feel the need.

Tyres for racing are usually narrower in suit the narrower rim profile and reduce weight, as well as roll faster on the racetrack.

Hubs

The centrepiece of a wheel, BMX hubs house the bearings on which the wheels spin and are typically made from alloy. Bikes or wheelsets at lower price points will feature open-cage ball bearings, which whilst cost-effective, are susceptible to more damage and are less durable than the alternative, a sealed or cartridge bearing. Cartridge bearings have the small steel balls kept within a sealed unit, and as such are protected from becoming contaminated by dirt and debris. Choosing a BMX bike or wheelset that features sealed bearings will mean a smoother and more reliable ride. The standard BMX axle size is 14mm, with flatland BMX bikes opting for 3/8” (10mm) axles for weight savings. The axle fits through the centre of the hub and then slides into the dropouts in the frame to keep the wheel in place, fastened with bolts. BMX bikes do not use quick-release systems.

BMX hubs come in four different types;

  • Cassette: Essentially the same mechanism as a mountain or road bike, the cassette hub uses an independent driver fitted onto the hub shell. Weighing less and generally easier to install and service, cassette hubs are the most popular choice for BMX bikes in both race and freestyle disciplines.

  • Freecoaster: Freecoaster hubs divide opinions in the BMX world, and are often only selected in order to help with certain tricks and are often only used by flatland riders. The point of difference is that freecoaster hubs have an internal clutch system that allows the rider to coast backward, so the wheel will actually drive backward without the cranks turning. Freecoasters are distinctly quiet when pedalling but will elicit a ‘clicking’ sound when coasting. Because of their more intricate design requiring more parts, these hubs are typically more expensive and weigh a bit more than a standard cassette hub.

  • Freewheel: These types of hubs used to be the standard, but have mostly been phased out in favour of cassette hubs. Freewheel hubs have the sprocket (sometimes referred to as the ‘driver’) threaded directly onto the hub shell. The smallest gearing available for a freewheel is 13-tooth, which is limits gearing options for freestyle riders (more about gear ratios and sprockets below).

  • Coaster: Coaster hubs are also known as ‘back pedal brakes’ whereby the ride will engage the brake when they pedal backward. Coaster hubs will almost never be seen on a freestyle BMX bike, with the exception of kids and entry-level bikes.

Gearing

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You may hear the words sprocket and chainring interchanged, but to keep it clear here we will refer to the chainring as the front ring attached to the cranks, and the sprocket as the rear driver attached to the hub.

Although BMX bikes don’t have multiple gears, the thing to consider is the number of teeth on the chainring and sprocket and the ideal pairing of these, also known as the ‘gear ratio’. To determine the gear ratio, you will need some basic mathematics. Simply divide the number of teeth on the chainring (say, 25) by the number on the sprocket (nine) and you will be left with 2.78 meaning the rear wheel will rollover approximately two-and-three-quarter times for every rotation of the chainring. The lower the number, the easier to pedal, the higher, the harder it is to pedal (requires more force).

In order to ride out of tricks and better clearance over features, the trend for freestyle BMX is to have a smaller chainring/sprocket combination than traditional or race BMX’s. A common gear ratio is 25/9 (referring to the chainring/sprocket respectively). This means it takes little effort for the rider to accelerate quickly into a trick or a jump, but means they are compromised on top and speed and power.

BMX race bikes need to allow the rider to generate explosive power, so a much larger chainring is used. Gearing choice on a BMX race bike gets quite in depth the more progressive the riding becomes, and because there are discrepancies between wheel sizes and tyre widths, it goes beyond simply gear ratio.

BMX racers will be choosing and changing gear ratios to match the rhythm and demand of different race tracks, or simply to suit their physiology or ability level. When looking to purchase, it is safe to trust the gearing for race bikes will be approximately 55 gear inches, which is likely to suit the majority of riders.

Cranks

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BMX cranks come in one-piece, two-piece or three-piece units.

One-piece cranks have the left and right crankarms and spindle all as one piece of steel. The arms thinner and are much more flimsy, only seen nowadays on kids bikes for very cheap BMX bikes. For two-piece configurations, the spindle is fixed to only one crank arm and the other is separate. These tend to be thicker and sturdier than the latter. Three-piece cranks are much stronger and have both crank arms and the spindle as three separate units Ideally, choose a BMX with a two or three-piece Chromoly crank for strength and durability.

Crank lengths can vary from 145mm up to 190mm - however most freestyle riders will opt for shorter cranks to allow for clearance when performing tricks, a common choice is 165mm. Race BMX crank size is dependent on rider height, and will sometimes be made of aluminium to reduce weight.

Pedals

The pedal of choice for all types of freestyle BMX is a wide platformed plastic pedal to reduce weight and are generally inexpensive. An added bonus is plastic is slightly less harsh than metal pedals should an (inevitable) blow to the shins occur. The pedal axle will be 9/16in on two three-piece cranks and 1/2in on one-piece cranks. It is important to know what size you have buying new pedals!

The preference for racing is to use SPD, or clip-in pedals. These pedals provide the rider with the ability to generate maximum power for and get up to speed as the gate drops.

Of course, if you are new to BMX, a flat pedal will suffice while building confidence in handling and gate starts.

Saddle

Saddles do not play as much of an important role in the setup of BMX bikes, so the preference for saddles is for minimalism, even so far as to having saddles that are completely plastic. Entry level BMX bikes will have a bit more cushion and larger surface area as again the assumption is that the rider will be sitting down and pedalling more than an advanced rider who will be floating above the saddle a lot.

  • Rails: Just like a mountain or road bike, the has rails on either side that sit in a clamp attached to the seat post.

  • Pivotal saddles: The saddle is connected to the seatpost vias a single bolt that goes through the middle of the saddle and into the seatpost.

  • Integrated seat/seatpost: Some manufacturers produce a complete unit that is the seat and seatpost integrated into one. Not ideal for sitting on, but reduces weight significantly.

Handlebars

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Image Jono Wade

Freestyle handlebars rise steeper than race BMX bars in order to be maneuvered better. Usually made from Chromoly or aluminium, the latter being lighter but more susceptible to fatigue, and steel will be heavier but dampen vibrations better and last longer.

Bars found on 24-inch BMX bikes might not have a crossbar and have significantly less rise to account for the higher stack due to the larger frame and bigger wheels.

Flatland handlebars usually have a very minimal sweep so the bars feel basically the same when pointed forward or backward, as well as a low crossbar so riders can swing their leg over for tricks.

Brakes

BMX bikes will typically feature rim-brakes, where the pads connect to the rim to slow momentum. Freestyle bikes are equipped U-brake that sits inside the rear triangle and out of the way of the rider. Many freestyle bikes may also come with a ‘detangler’ or ‘Gyro’ braking system for the rear brake.

Distinguishable by the division of two cables around a mechanism fitted at the headtube, the detangler allows the bars to spin a full 360 degrees without the brake cable getting tangled. This is incredibly helpful for advancing tricks such as barspins and tailwhips. If these sorts of tricks are not going to be on your radar, a normal brake will suffice.

Although a front brake is allowed in racing, it is not necessary with most racers opting for a strong, linear-pull rear brake only, also called V-brake.

Accessories

  • Helmet:

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Helmets for freestyle BMX cover a large proportion of the head and take a more ‘bowl’ shaped look than the low profile, highly-vented road cycling helmets. These helmets will have minimal vents and can extend to covering the ears as well. This is to take into account that BMX riders may take a stack while attempting a trick and are at risk of landing in any direction. When racing BMX, there are rules and restrictions around equipment on the racetrack. In training and competition, a full-faced helmet must be worn along with long pants and long-sleeved jersey.

  • Gloves: Regardless of whether you're riding freestyle, or racing your BMX bikes, full fingered gloves are a must. BMX specific gloves will typically feature grip on the palm of the glove that extends to the tips of the fingers.

  • Shoes: If you are riding with clip-in pedals, look for some mountain bike or BMX specific clip in shoes that offer a good amount of stiffness and comfort.

  • Pegs: Pegs are metal cylinders (or sometimes dense plastic) that are fitted to the axles of the BMX bike so the rider can balance on them for tricks in flatland, or perform grinds on rails or ledges in street and park riding. Flatland will usually have pegs on all 4 axles, whereas street riders will have just one side with pegs on the front and rear. Pegs are strictly banned in BMX racing.

Kids BMX’s

Buying a BMX for anyone under the age of 12 is a good way to get them on the bike in a fuss-free fashion. No gears and a sturdy frame mean kids can experiment and find their comfort zone with riding a bike along with tackling a range of terrain including footpaths hard packed dirt trails.

Kids BMX bikes are available as scaled-down versions of adult 20in bikes, with some brands offering Chromoly steel 16in and 18in freestyle bikes. Race BMX bikes are available as ‘mini-micro’ and ‘micro’ for kids getting into racing.

More traditionally, at the lower price point, a high-tensile steel frame will come equipped with a coaster brake, one-piece cranks, training wheels and accessories such as chain guards, a basket or frame pads. These are suited to younger kids just getting on their first bike but are not designed to take the hits that a freestyle BMX will. If a child is showing interest in finding new limits and trying new things, it might be time to update the equipment to match the skill.

For information on what to know about kids bikes, see our comprehensive buyers guide

Let’s Talk Budget

Most kids bikes will fall into this category, with the lower end offering one-piece cranks, hi-tensile steel frames, and more beginner level gearing. Sealed bearings might be non-existent or found in the rear hub only. Expect to see single walled rims for the lower end of the spectrum.

A Chromoly frame will typically feature at this price point along with, two or three piece cranks and accessories like stunt pegs. Upper end may see Gyro brakes and smaller, lighter chainrings with sealed bearings featuring both in the wheel hubs and the bottom bracket.

BMX bikes of this level will often be custom built, feature the lightest and strongest Chromoly parts. Expect to see luxuries such as lighter hubs, stronger rims and sealed bearings in the hubs, bottom bracket as well as the headset. If BMX has become an all-consuming hobby and the riding is becoming more progressive, the equipment offered on bikes at the top-end of the spectrum is likely the best you can get.

Where to shop

BMX freestyle bikes can be found in most bike shops, although the range may be limited. There also exists BMX only shops who will have expertise specific to BMX and are highly to be dedicated BMX riders themselves so will be able to answer your questions authentically. Shopping at a BMX specific store is a good option for custom built bikes or wheels. The same goes for BMX race bikes, because the market is niche, there are stores that specialise in this discipline and can offer first hand and expert advice on the spot.

BikeExchange is the perfect place to find yourself a great deal year-round and here are some tips to help you narrow in on that bargain:

  • EOFY: End of financial year is a great time to buy a bike. Retailers are looking to clear old stock to make way for new, creating the perfect opportunity to get a great price on the current or last years model.

  • Christmas: Christmas is another good time of year to get a bargain. Christmas is the busiest time of year for retailers and the bike industry is no exception. Many retailers will try to clear old stock that didn't sell during the end of financial year period or add sweeteners such as a helmet or gloves.

  • Buying online: Buying online from a manufacturer cuts out the middleman, reducing the overall cost which is then passed on to the consumer. This can be a great way to save money but should be approached with caution. Buying online has its pitfalls; you generally can't inspect the bike, take it for a test ride, check if it fits, assess unique features, make alterations or ask questions. It's a risky game unless you know your exact size and specifications.

  • Buying Used: Many BMX race clubs, or online forums will either have a relationship with a BMX dealer or will list bikes for sale within the club, either new or used. Additionally, the BMX club can help advise what to look for when you are first starting out with racing. Of course, always be somewhat cautious when buying a used bike as you don’t want to find out later you have been short-changed.

Popular Brands

Got an idea of what you’re after but unsure on where to start looking? Popular BMX brands include Eastern, Colony and Fit Bike Co.. If it’s a race bike you’re after options from Haro, DK, GT and SE are a great place to start looking.


We hope this buyers guide has been helpful and provided some valuable information. You can browse BikeExchange for BMX bikes, or search for your local bike shop to get further assistance.

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