the same for the frame. Mountain bikes - 24- or 26-inch wheels and either rigid forks or forks with short front end suspension (usually 80–100 mm travel, but can be up to 203 mm depending on the type of the bicycle). A firm suspension is desirable for dirt jumping. 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 Double the most common form of dirt jumps. This consists of two separate earthworks, one acting as a takeoff (lip), and the other as a landing. Also known as a "gap" jump. They can be "Step-Ups", where the jump's up ramp is lower than the down ramp and the rider loses speed, or "Step-Downs", where the jump's down ramp is lower than the up ramp, meaning that they gain speed. Tabletops are more common among those new to the sport, they are a single earthwork with a takeoff at one end, and a landing at the other, with a flat 'table' on the top. These are favoured by new riders because when the rider comes up short they can still easily ride out of it. Ski Jumps consist of just a takeoff, they're usually longer and