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 gearings such as 25:9, 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 lightweightframe. Suited to bigger jumps or more challenging competition courses. Other types of dirt jumping bikes include: Freestyle Motocross (FMX, Moto-X) of various sizes & engine sizes. Dirt Jump/Freestyle mountain bikes look similar to mountain bikes but usually have a rigid frame and a lower stand-over height, in order to keep the seat out of the way while performing tricks. Some high end DJ frames also have short travel rear suspension, sometimes with bottom-bracket-concentric pivots to allow singlespeed use. The wheels are usually more robust than a cross country mountain bike's and