What Is Dirt Jump Mountain Biking? The Basics Explained
Not to be confused with dirt biking (i.e. motocross), dirt jump biking is its own sport altogether. While it shares similarities with freestyle motocross like the dirt surface, speed, style and getting airborne, dirt jumping is done on nimble bicycles and entirely without a motor. It’s pretty simple when broken down. So here is what dirt jump MTB is in a nutshell:
Dirt jumping is the biking discipline of hitting jumps entirely made of dirt or soil. Not in a competitive scenario but purely for the fun of it. It’s done on purpose-built tracks with smooth surfaces and no natural obstacles, only man-made dirt-to-dirt jumps and occasionally berm turns.
In other words, dirt jumping reduces biking to the essentials of jumping a bike, making it an excellent sport to learn how to jump. It involves riding “dirt jumper” bicycles over ever-increasingly high jumps to get airborne. The intent is not to compete on a course at high speed but rather to perform tricks over the jumps.
The goal is to develop control and eventually style while in the air.
Why dirt jump MTB is fun and good training
Dirt jumping (or DJ) is everything that the original Motocross Freestyle is but without an engine. It’s all about the freedom to express style while in the air. Tho riders build speed and momentum entirely by jumping high and landing cleanly.
Much like pumptrack riding, DJ forces riders to focus on basic biking skills in order to ride well and improve. No sharp turns, no roots, no rocks – only jump after jump.
Bike handling, balance, timing, stamina and explosive strength are needed in order to perform well.
Jumps come up in quick succession with only minimal time and distance spent on the ground between them. Landing correctly and setting up the next jump need to happen fast in order to be able to complete the full set of jumps from start to finish. The short bursts of high intensity are guaranteed to get your blood pumping!
The dirt jump courses
The courses are fairly unique in that the jumps are built unusually steep so that riders go high over them rather than far. Quite the opposite of what you would expect in the aggressive discipline of Downhill MTB where speed is key. Because more dirt is needed to build jumps high, there is generally a gap between take-off and landing. This is a so-called double jump or simply “double” because it involves two obstacles: lip and transition.
It’s a common style of MTB jumps and is almost exclusively found on dirt jump trails. Variations include the step-up (preferred for trick jumps), the hip jump and the step-down to build speed. All of those and more are explained in this article on all the variations of bike jumps.
Jump trails are usually found in a bigger park with multiple lines to choose from. Beginners and pro riders can work on their skills next to each other. Dirt jumping is one of the few MTB disciplines where parallel riding on different difficulty trails is possible.
Differences between BMX and Dirt Jumping
The discipline of BMX is race-oriented, and dirt jumping is focused on having fun without the competitive aspect. You could say dirt jumping is the loose side of BMX (short for Bike Motocross) and the rigid bikes are perfect for dirt jumps.
Both BMX and DJ started around the same time. While jumps are a major part of BMX racing, getting airtime is fun but not the fastest way forward. So racers tend to squash or scrub jumps, while dirt jumpers go as high as they can for maximum airtime.
The courses have evolved accordingly to lean more into the defining aspects: speed or style. The “goal” in dirt bike jumping is not to race against the other bikes and compete on speed; instead, it is to enjoy the feeling of weightlessness and maybe even do amazing tricks over the jumps.
The bikes Dirt Jump riders use
A dedicated dirt jumper bike has a smaller frame than a traditional mountain bike and gearing that is designed to produce more torque than speed. All extra weight has been stripped from the dirt jumper, making it capable of jumping high and being maneuverable mid-air.
It is possible to purchase specialized mountain bikes, known as “dirt jumpers”. However, they could also be called Pumptrack Bikes, Slopestyle Mountain Bikes or Dual Slalom Bikes.
This kind of bike is used for all these MTB disciplines. Alternatively, conventional BMX bikes are just as good for dirt jumping. And on top, their widespread use makes BMX bikes a great affordable option to enter the sport.
Dirt Jump frames are mostly out of alloy. They’re designed to be durable instead of as light as possible. The overall construction has to be of good quality because they are exposed to very high forces during normal operation and especially when things don’t go as planned.
In terms of sizing, it’s kept very simple: most bikes are one-size constructions. Some rare manufacturers offer two frame sizes to suit large riders better.
Dedicated dirt jumpers have wheels sized between 24 inches and 26 inches. BMX bikes are on the smaller end with wheels at 20 or 24 inches.
The tires installed on the dirt jumper’s wheels are heavy-duty treaded rubber designed to withstand the shock loading imposed on them by the jumping and landing compressions.
Besides wheel size, the suspension (or lack thereof) is the other major difference between dirt jump MTBs and fully rigid BMX bikes. A short-travel front suspension fork is the trademark of a dirt jumper. A stiff rear suspension is also possible, but not as common. It can help with landing on bigger jumps and can iron out mistakes, but also requires maintenance.
The braking system is minimal. It used to be a standard rear V-brake, and disc brakes are becoming more popular in the community. Just front brakes are still uncommon.
The choice of seat divides the riding community, where some riders prefer a padded seat to provide contact points during the inflight tricks, while others feel that the seats are too large and get in the way on the small bike. Either way, saddles on jump bikes are not there to sit on anyways. And whatever the saddle width, it’s usually slammed down as far as it can go into the frame without touching the rear wheel.
The single-speed gearing is as simple and fail-proof as possible. It’s designed to produce torque rather than speed. The most common gear ratios for dirt jump bikes are the following.
And sometimes even smaller gear ratios like 25:9, referred to by the riders as “micro gearing.”
Differences between dirt jump and slopestyle MTB
Now, you might say hitting jumps and doing tricks on an MTB sounds a lot like slopestyle to me. And you would be right!
Slopestyle is the competitive mountain bike discipline with the goal of performing mid-air acrobatics over gigantic, smooth jumps to achieve a high points score. The courses have a variety of features from dirt-to-dirt jumps, ramps, wood features, and other innovative designs to test the riders.
The gaps, heights and distances are bigger than on regular dirt jumps. The more airtime, the more time there is for tricks and even difficult trick combinations. Full-suspension dirt jump bikes are the norm here and so are full-face helmets.
Slopestyle is where mountain biking and BMX separate into their own thing.