Though originally denoting a bicycle intended for BMX racing, the term "BMX bike" is now used to encompass race bikes, as well as those used for the dirt, vert, park, street, flatland and BMX freestyle disciplines of BMX. BMX frames are made of various types of steel and (largely in the racing category) aluminium or carbon. Cheaper, low-end bikes are usually made of steel. High-range bikes are mostly Chromoly or high tensile steel, although the latter is noticeably heavier concerning strength. High-performance BMX bikes use lightweight 4130 Chromoly or generation 3 Chromoly.
The introduction and widespread popularity of the cassette hub and free coaster have ushered in smaller gearing on BMX bikes. Instead of the old 44/16 gearing found on almost all older BMX bikes and current BMX racing bikes, new freestyle bikes use gearing such as 36/13, 33/12, 30/11, 28/10, 25/9, 23/8, and even 22/8, all of which have similar gear ratios around 2.8:1. Advantages of smaller gearing hubs include lighter weight and more clearance when grinding. Freecoaster hubs are popular among street and flatland riders. A freecoaster allows the rear wheel to roll backwards without engaging the hub and forcing the cranks to rotate backwards as they would on a normal freewheel or cassette style hub. However, many riders still prefer cassettes as they engage more quickly when pedalling forward and tend to cost slightly less.
On most freestyle, street, and park BMX bikes, the wheels have 36 spokes. Race bike wheels also usually have 36 spokes, but wheels for the smallest racers, sometimes as young as three years old, can be built with 18 or 28 spokes. More aggressive riders may opt for wheels with a spoke count of up to 48 spokes. However, hub and wheel combinations for this are becoming difficult to source.
BMX Racing bike wheels vary in size, from 16" to 26", with 20" being the most popular.
Dirt jumping and freestyle bike wheel sizes include 16" and 18" for younger, smaller riders, 20" for most other riders, and a few companies, including Haro and Sunday, offer 24" freestyle bikes for taller or older riders who feel cramped on a standard 20" BMX bike.