Dirt jumping

Dirt jumping is one of the names given to the practice of riding bikes over cement type jumps of dirt or soil and becoming airborne. The idea is that after riding over the 'take off' the rider will become momentarily airborne, and aim to land on the 'landing'.

Dirt jumping can be done on almost anything with wheels, but it is usually executed on a dirt jump bike.

• BMX bike built for dirt jumping tends to have a longer top tube than a street BMX bike, and may well be more reinforced. They will rarely have pegs fitted (unless they are also used for street riding or unles the person wants to execute a peg grab), and will generally run only a rear u-brake. Also, the tires will be treaded, as opposed to the slicks and semi-slicks used for park riding. Large, padded seats are also popular as something to land on when a trick fails, and are also easier to hold for in-flight tricks; but very small seats are also a style for the more "hardcore" riders. The gear ratio is generally around 44:16, though using small gearings like 25:9, known as 'micro gearing', has become popular in the present day.A photo of some BMX trails courtesy of barendbmx.co.uk
• Hybrid BMX/Jump bike - a scaled up BMX with 24" wheels. Strong alloy rims and lightweight chromoly frame. Suited to bigger jumps or more challenging competition courses.
• Freestyle Motocross (FMX, Moto-X) of various sizes & engine sizes.

* Dirt Jump/Freestyle mountain bikes look similar to mountain bikes but have a rigid frame and, a lower stand-over height, this keeps the seat out of the way while performing tricks.  The wheels are usually more robust than a cross country mountain bikes and the same for the frame.  Frames are built for a balance of strength and lightweight.

• 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) 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 is very common, as is using only a rear brake. In modern times, 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" wheels, a gear ratio of approximately 60 gear inches (~36:15 on a 24" rear wheel or ~36:16 on a 26" rear wheel) and rigid or 80-100mm travel forks. An 'all-round' bike used for dirt jumping will more likely have 26" 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. Dirt Jump bikes are made by a variety of companies. Examples of commonly purchased bikes for the general purpose of dirt jumping include the Kona Shonky or Cowan, (Kona also have a line of trail oriented bikes that are also suited for dirt jumping, the Shred and Stuff) Specialized P.1, P.2, P.3, Norco 125, 250, Havoc or Ryde, Transition's Trail-or-Park, Bank or Double, Giant Brass or STP, Devinci District, Haro Thread and Porter, Blk Mrkt Mob, Riot, Contraband, Killswitch, Soldier or Malice, NS Majesty, Suburban or Capital, Dobermann Pinscher or Molosse, Trek Ticket Signature, Eastern Nightrain, Thunderbird, and Mad Dog, the Banshee Amp or Rampant, and khs awesome line up of dirt jumpers the dj and sj series.

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 more stability and to spread the load of heavy lands. most of these "micro geared" bike run 85 to 100 psi tires. these are usually threaded and made with kevlar bead to prevent pressure flats and tears.

History

Dirt Jumping evolved alongside BMX racing from its birth. Dirt Jumping is similar to BMX or Mountain Bike racing in that the rider jumps off of mounds of dirt. 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 best tricks with the best style. Trails are most often hand built, with attention to detail. Dirt jumping has evolved a lot over the years now, there are now competitions that you can compete in for prizes. The dirt jumps have become much larger and better built. They now use diggers and other machines to help build and compact the dirt quicker and more efficiently. The dirt jumps which are sometimes even built with wood can even be up to between 20 and 30 feet long for the professionals. The tricks have evolved a lot partly due to freestyle motocross evolving where a lot of the dirt jumpers get their inspiration from. When it first started it would be just tabletops and whips as the main tricks, now nearly every professional can back flip, front flip and even double back flip.

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 upramp is lower than the down ramp and the rider loses speed, or "Step-Downs", where the jump's downramp is lower than the upramp, 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 flatter than other jumps, and tend to be situated on downhills, so the slope of the hill can serve as a landing. They're used mostly in competitions on jump length.
• Rollers are small tabletops that give you extra speed by 'pumping' the jump. You usually would find these at the beginning of a trail.
• Step ups are ramps just before inclines to enable rider to jump from the top of the incline.
• Whoops/Rhythms a series of three or more small rounded ramps close together to enable rider to 'manual' over them.
• Spine is one earth work with a take-off and a landing, but no table or gap, made to get higher air without distance.
• Berm basically is a curved wallride that comes out of the ground. Mostly used on sharp turns in which helps you by giving you the ability to ride on your side. The curve allows you to make a sharper turn. Mainly used on downhill trails but, also used dirt jumping to avoid hitting trees. They are also used to maintain your speed without having to brake on turns. Some trails consist of jumps that lead into berms.
• Hip Jumps consist of the landing being anywhere within 0 - 90 degrees, left or right of the take off enabling you to transfer.