Airtime features

1. Overview

  • ‘Airtime Features’ are all the elements of a trail that are built as ‘jumps’ where the shape of the trail helps take the rider and their bike off the ground into the air.
  • The main benefit of ‘Airtime Features’ are that riders find them fun and can use them to find ‘flow’ on the trails.
  • ‘Airtime Features’ are a relatively high risk as there can be significant consequences, resulting in serious injuries, if the rider gets it wrong or if the shape of feature is poorly designed and/or constructed.
  • ‘Airtime Features’ should be constructed to the correct level for the experience of the rider, including considering the run-in speed, size of the feature, landing zone, and fall zone should all be considered at the planning and design stage.
Shape of Airtime Features/Jumps
  • In terms of shape, jumps can be very different and it is possible to be very creative.
  • There are a few consistent points that are important to consider when building a jump. Long take offs with constant transitions (shape doesn’t change suddenly) help make a jump as safe as possible. It’s the same for the landings, and it’s even better if they are wide and free of obstacles so it’s a “safe spot“.
  • One difficult task is to link airtime features together or in the section of trail with the right speed and rhythm.

2. Anatomy of airtime features

A jump can be divided into 3 elements, the take-off, the deck (or gap) and the landing. The take off is composed of a transition (to take the momentum) and a lip that allows the bike to leave the ground.

2.1 Set up feature – roll-in / drop-in, roller

It’s a feature which manages the speed of the rider entering the air time feature. Roll-in speed and the size of the air time feature have to be adapted to the trail level.

2.2 Transition

The transition is the curve where the trail-grade increases. As the compression force rise it has to be a very solid surface and a smooth curve all the way up.

2.3 Lip

  • The lip is critical because it is the last part that riders are touching before take off.
  • To make sure the jump is safe and predictable, it has to be straight, smooth and in line with the transition angle. Make sure there is no angle between transition and lip.
  • As the lips (and the top of the transition) are in many cases the steeper surfaces, it is the most exposed to erosion. Control them regularly.

2.4 Deck

  • Decks can take many forms and sizes according to the trail level and run-in speed.
  • On easy trails, mellow deck as the elephant backs will be favoritized.
  • On more difficult trails, inexisting deck can be found on a gap jump for exemple. Mandatory jumps have to be announced at the trail entry. Road/river/canyon gap can be found on a double black trail.
  • The lenght of the deck is one of the most important parameters on a jump feature.
  • It has to match the run-in speed and be accorded with the height and angle of the take off as well (see figure 1).

2.5 Landing

  • The landing steepness must meet the take off needs to match the flight trajectory. (see figure 1)
  • It is a zone that needs to be smooth and free from obstacles (think about fall zones as well).
  • The longer it is, the safer.

2.6 Transition

  • Mellow transitions will decrease compression forces on riders.
  • Abrupt transition can be dangerous.
  • This is where the eroded material from the landing will be deposited from the water and rider tear and where it can be picked again to smoothen the landing.

2.7 Water management

  • Take off and landing are 2 sensible zones to erosion as it is impossible to drain the water half way in.
  • The steeper and longer they are, the more sensible they will be.
  • Frequent controls are needed to keep them safe.
  • Water has to be drained at the top of the feature and in the compressions before and after.
  • Make sure to have drainage far away enough from the transitions to keep them dry and compact as this is where the biggest compression forces will occur from the riders.

2.8 Speed management

  • Speed management is key when it comes to airtime features considering two points of view: Rider flow and safety and trail erosion/sustainability.
  • Even if bikes have pedals and brakes to generate or reduce speed, jumps must be built according to the natural section speed and riders shouldn’t be expected to pedal or brake in front of a jump.
  • It’s about the predictability of a trail. Choosing the right type of jump, size and angles is crucial for an optimum rider experience.
  • The limit between a fun and a dangerous jump can be very thin and can evolve in time or with trail surface conditions (dry or muddy).
  • Try to build jumps that allow for margin error, that can accommodate a wide range of speed and level of riders. For example longer and less steep take-off and landing are more forgivable. Decks or step-up shapes as well. Gap features should be kept for black runs and warned clearly.
  • Step down jump will create speed whereas step up features will slow riders down.
  • A good combo is to start a line with a step-down jump to generate speed, then build a few table-tops or double jumps and finish the line with a step up to reduce speed before the next turn or next section.
  • Building a step-down jump on a steep section without a natural way to slow down (leading to an uphill) can lead to heavy braking, rider and water erosion and a lot of maintenance work.

Figure 1: Exemple of a sustainable jump line

Figure 1: Exemple of a sustainable jump line

 

3. Most common airtime features

3.1 Table Top

The take-off and the landing are in line, with a solid “deck“ between the take-off and landing. it is not possible to fall between the take-off and the landing. These jumps are the safest because they are rollable by the less experienced riders. However, it requires having enough materials available for the construction.

Figure 2 : example of table top jump

 

3.2 Double

A double is a jump with an “empty“ space between the take-off and landing and you need to jump from the take off to the landing. Double can be man made in a bike park but can also be a jump between two natural features, one being the take off and one being the landing.

It’s not harder to jump a double than the Table Top but it can be even more impressive for the rider if there is a gap between the take off and the landing. An advantage of building a Double is that it requires less material than a Table Top Jump.

Figure 3 : example of a double  jump

 

3.3 Gap Double

A gap double is as double jump but with a more pronounced gap or empty space between the take-off and landing. It’s not harder to jump a Gap than the Table Top but it’s way more impressive. It can therefore be complicated for riders who aren’t very experienced.

Figure 4 : example of a gap jump

 

3.4 Step-Down

A type of jump where the rider jumps from a higher elevation down to a lower elevation of the trail. The difference with a drop is that the take off has an angle. It can be built as a table or a double

Figure 5 : example of a step down jump

 

3.5 Step-Up

A type of jump that sends a rider up from a lower elevation to a higher elevation on the trail. It can be made of dirt, wood or even a metalic ramp. It can be built as a table or a double.

Figure 6 : example of a step up jump

 

3.6 Drop

A technical trail feature where the trail’s elevation abruptly changes at a steep enough angle so that your front tire cannot easily roll down to the lower elevation. It can also describe a jump from a woodbridge or a rock generally at low speed.

Figure 6 : example of a drop jump

 

3.7 Hip

The landing of the jump is offset (angled 45-90 degrees) to the take-off. The hip can be combined with a step up or step down but the rider will still need to change the orientation of his bike in the air.  It can be built as a table or a double.

Figure 7 : example of a hip  jump

 

3.8 Whale Tail

The name comes from the shape of the jump which resembles a whale. The hump is used as a landing for one jump and the tail is used as a lip for a second jump. This requires the rider to be attentive because the interval between jumps is relatively short. Depending on the height, barriers can be installed on the sides to prevent falls.

Figure 8 : examples of a Whale Tail jump

 

3.9 Elephant Back

A table top, step-up and roller combination. The addition of a roller on the last 2/3rds of the table top jump creates a step-up. Step up jumps are less intimidating as more air can be gained without going further from the ground. The roller also helps to prevent riders casing the jump and ending up 50:50; Front wheel on the landing and rear wheel on the deck of the table top jump. This type of landing is safer and reduces maintenance.

Figure 9 : example of an Elephant back jump

 

4. Key Considerations

4.1 Key Aspects when building jumps


Difficulty
:

  • Jumps are fun but can be dangerous.
  • Make sure the type of feature, the size and technicality, correspond to the announced level of the track.
  • It is recommended to use rollers or mellow tabletops on beginners’ tracks.
  • Unrideable gap or drop jumps must only be found on expert or proline and must be announced at the trail entry.
  • Ride-around lines can be considered but are sometimes a dangerous option on crowded tracks with people merging at the back of jumps.

Security :

  • Jump lines are often where crashes happen. Make sure to anticipate fall zones and rescue access.
  • Plan it on a zone protected from the wind.
  • As jumps need speed to be cleared and the undulating terrain can hide what is happening in the back of a jump, it is better to protect jump tracks from any other riders, kids or dogs from crossing or sitting behind a jump. Jump lines are always a one-way direction and if build on a jump park, plan a clearly separated path to go back to start.

Speed management: see 2.8 above for more details.

 

Building techniques :

  • Shapes and sizes of jumps are very tricky to build right and can become dangerous when build wrong.
    • It is very hard to plan because it goes according to speed which is hard to predict.
    • A lot of riding and building experience is needed when it comes to creating airtime features.
  • A rough shape is done first with a machine and the available materials.
  • Then, angles are adjusted depending on user level, arrival speed and length to cover.
    • Take off angles: As mentioned 45° seems like an ideal angle considering the length and height you want to launch the riders.
      • Flatter take-offs can be less technical to manage and are mostly used on beginners ‘trails.
      • Steeper take-offs are sometimes more fun but harder to manage for riders. They can quickly become dangerous for less experienced levels.
    • Landing angle: The angle of the landing must meet the take-off angle (see figure 2). The longer the landing is, the more forgivable it will be considering the landing margin.
  • It is good to build the trail a bit wider when it comes to jumps. Riders appreciate having a bit of room for error on airtime features.

Maintenance :

  • The transition is where the bikes are pushed against the ground.
    • If the ground is not firm enough (wet or not compacted enough) ruts will appear which is very tricky to negotiate for the rider.
    • Make sure to build it properly and to have regular maintenance checks (even more on bad weather periods).
  • The lip needs to stay smooth as it is the steepest area of a jump and the last surface the rider will touch before take-off.
    • Its steepness makes it a very sensible zone concerning water erosion.
    • It is important to smoothen the lip and control the general take-off curve regularly.
  • Landings can sometimes reach very big sizes and surfaces.
    • It needs to be clean for a smooth landing.
    • It is impossible to build any drainage in the landing area. Water can accumulate and start eroding the trail surface.
    • Regular maintenance checks are necessary to prevent gully from being dug by the rain.
    • After exceptionally heavy rain, it is essential to proceed to a track check before opening to the public.

Depending on the speed and the level of riding of the rider, the take-off angle and the landing might be adapted. The ideal angle for jumps is around 45°.

Photo 1: Gap double with a bypass line and warning sign, source: https://www.dirtscrolls.com/14974019-hot-springs-arkansas

 

5. Additional reading & Media

  • Trail Solutions – IMBA’s Guide to Building Sweet Singletrack – P.231 Part Eight: Building Challenging Trails
  • IMBA – Guidelines for a Quality Trail Experience – p. 53 Chapter 4 – Creating Trails and Trail Features
  • Allen, B. (2014). Bike Parks: IMBA’s Guide to New School Trails – p.101 – Chapter 6, construction