Dirt jumping is the practice of riding bikes over jumps made of dirt or soil and becoming airborne. Dirt jumping evolved alongside BMX racing and is similar to BMX or mountain bike racing in that the rider jumps off of mounds of dirt, usually performing a midair trick in between. It differs in that the jumps are usually much larger and designed to lift the rider higher into the air. Additionally, the goal is not to complete the course with the fastest time, but rather to perform the tricks with the style. Dirt jumping can be performed on BMX bikes or specialized mountain bikes known simply as "dirt jumpers".

Dirt jumping bikes

Dirt jumping uses a specific kind of bike. BMX, for instance, has a range of bikes built for this activity. One of its key differences from general purpose bikes is the fit. There is only one standard BMX dirt jumping bike frame, which is meant to fit all riders, young and old. These bicycles tend to have a longer top tube than a street BMX bike and are often more robustly built to withstand the poundings from the jumps. They will rarely have pegs fitted. Traditionally, DJ (dirt jump) bikes ran only a rear v-brake but disc brakes are becoming more common. DJ tires are treaded - the heaviest treads of all the BMX bikes - as opposed to the slicks and semi-slicks used for park riding. The wheel size is mostly 26-inch. Some riders prefer large, padded seats for in-flight tricks while others do not find seat size an issue. The gear ratio is generally around 44:16, 36:13, 33:12, and 30:11, although using smaller gear ratios such as 25:9, also known as 'micro gearing', has become popular. There is also the so-called hybrid BMX/jump bike, which is a scaled-up BMX with 24-inch wheels. Strong alloy rims and a lightweight frame. Suited to bigger jumps or more challenging competition courses. Other types of dirt jumping bikes include: A mountain bike built for dirt jumping tends to have a smaller frame than what is used for other disciplines. Running singlespeed with one brake is very common. using single or dual disc brakes has replaced the use of only one rear V-brake. In general, a mountain bike dedicated to dirt jumping will have 24- or 26-inch wheels, a gear ratio of approximately 60 gear inches (~36:15 on a 24-inch rear wheel or ~36:16 on a 26-inch rear wheel) and rigid or 80-100mm travel forks. An 'all-round' bike used for dirt jumping will more likely have 26-inch wheels, a 25-36 tooth chainring with a wide-ratio cassette and a short- to mid-travel fork. Mountain bike dirt jumpers are usually split on the basis of wheel size because the wheel size dictates the shape of the takeoff to an extent. A 20-inch BMX bike for dirt generally has a 48-spoke rear rim and a 36-spoke front to prevent rim collapse in the case of casing a jump. The frame is a little bit longer to aid in stability and to spread the load of heavy lands. Most of these "micro geared" bikes run 85 to 100 psi tires, and tires are usually threaded and made with kevlar bead to prevent pressure flats and tears.

Types of jumps

Types of acrobatics