The vast majority of freestyle, park and street BMX frames are made from steel, which is light enough to perform tricks in the air but tough enough to take the punishment of crash landings on concrete.
BMX frames at the upper end of the market are built with 4130 chromoly steel, or ‘cro-mo’, a chrome-molybdenum alloy that is light and strong, with a plush feel that experienced riders appreciate. More budget frames usually feature frames and forks made from hi-tensile (‘hi-ten’) steel, which is strong enough to take the punishment of BMX riding but a little heavier than cro-mo with a harsher ride feel.
Some BMX racing frames use strong, stiff and lightweight aluminium or carbon fibre frames, where the emphasis is more on speed and less on ability to take abuse. However for non-racers, steel is the frame material of choice.
The BMX frame you choose will depend on the type of riding you do. There are three main categories of frame: race, freestyle/street and cruiser.
• Race frames are made for Olympic-style track racing and are built lighter to improve speed. They are not suited to tricks or hard impacts on concrete.
• Freestyle/street frames can turn their hand to a number of things, including skatepark riding, vert ramp riding and dirt jumping. These bikes often have a gyro for barspins, pegs for riding rails, and brakes, although some street frames for flatland-style riding are more minimalist, and run brakeless.
• Cruiser frames: These are bigger than standard BMX frames and designed to run 24” wheels as opposed to 20”.
BMX frames are sized in terms of length. For street, ramp and dirt jumping the most popular size of frame is a 21″ top tube, giving airborne riders room to swing the bike underneath them. Bikes designed for flatland BMX, where tricks and stunts are performed on a flat piece of ground with no obstacles or ramps, tend to have shorter frames (20” or less) for precision control and balance.
However taller /shorter riders may choose longer/shorter frames according to their personal preference. The below table should give you a rough guide as to how to choose a frame based on your height, but the best advice is to try out a few different sizes from friends to see which one suits your body and your riding style the best.
As with all bike frames, differences in BMX frame geometry will affect the bike’s handling. As well as top tube length (outlined above), some of the main things to consider are head tube angle, seat tube angle and chainstay length.
• Head tube angle: This primarily affects steering response, with a steeper head tube angle (75-75.5 degrees) positioning the rider further over the front end of the bike for sharper steering (also makes it easier to do technical tricks like nose manuals). A slacker head angle (74-74.5 degrees) puts the rider farther back on the bike and improves stability and handling at speed. Generally frames for street, freestyle and technical riding will have steeper head angles, and frames for park, dirt jumping and racing will have slacker ones.
• Seat tube angle: Seat tube angles can range from 69 to 71.5 degrees, with a slacker (69-degree) angle increasing the length of the top tube for extra stability. Again, as with head tube angle, steep equals technical sharpness, slack equals stability at speed – most riders will need to find their own ‘sweet spot’ between the two.
• Chainstay length: Shorter chainstays (and a shorter overall wheelbase) will make it easier to pop up on the back wheel for manuals and tricks. Longer chainstays (and a longer overall wheelbase) contribute to stability at speed. Again, technical street riders look for short, snappy bikes while racers and jumpers want a longer wheelbase for stability and security at speed.