A Giant Faith 2 downhill mountain bike with 6.5 inches of travel in the front and 8 inches in the rear.
Racing a downhill bike at Horseshoe Valley In Ontario

A downhill bike (also known as a downhill mountain bike) is a full suspension bicycle designed for downhill cycling on particularly steep, technical trails. Unlike a typical mountain bike, durability and stability are the most important design features, compared to lighter, more versatile cross-country bikes. Downhill bikes are primarily intended for high-speed descent, and downhill riders will usually push, or shuttle via chairlifts or motorized vehicles, to the trailhead.[1] Downhill bikes share similarities with freeride bikes due to their large strong frames and increased travel.[1]

History

Geometry

These bikes will also have very slack head tube angles (63 degrees or less),[2] long wheelbases (over 45 inches or 1,143 mm),[2] and will accommodate the use of up to 2.5-inch (63.5 mm) width knobbed tires. Downhill frames are also overbuilt to handle the stress of riding over rocky terrain, drops, and jumps. Bike weights have been typically over 34 lb (15.4 kg), but modern downhill bikes have broken the 30 lb (13.6 kg) weight barrier (with some custom builds on carbon frames weighing between 27–29 lb (12–13 kg)). Some newer (2014/5) downhill bikes can be built to weigh under 30 lb (13.6 kg), such as the Trek Session 9.9 or Kona Supreme Operator. Dual crown e-bikes typically weigh 25–35 kg (55–77 lb).

Adjustable head tube angles are also available to adapt the bike to the owner's preferred style of riding.[3]

Components

Suspension

Will typically have 7–10 inches (178–254 mm) of rear suspension travel, and be designed around a 7–8-inch (178–203 mm) suspension fork.[2] The suspension sag is also much higher than cross-country bikes (25%-50% of total travel vs. 10%-20%) for a more supple ride at higher speeds.

Fork

Other innovations include the use of OnePointFive head tube standard, which uses a 1.5 in (38 mm) wide steerer tube, instead of the more conventional 1.125 in (29 mm) diameter, for added stiffness and strength.[4] Most downhill bikes use dual crown forks which allow longer travel at the front(usually 203 mm or 8 in and increased stiffness that a single crown fork cannot offer. Drawbacks though, are increased weight and reduced turning radius.

Brakes

Downhill bikes usually have hydraulic, quad piston disc brakes, and the discs may be 200 mm or larger.[5] Brake discs and calipers may come with finned heatsinks for better heat dissipation.

Drivetrain

Downhill bikes usually have a chain guide to prevent accidental chain derailment. Some manufacturers are experimenting with internal gearboxes for improved reliability. Cassettes will usually only contain a few small sprockets instead of the 12 sprockets found on other types of mountain bikes.

Tires

Downhill bikes need very strong tires and wheels. The standard wheel size for downhill bikes is 27.5, but with recent changes to UCI World Cup Downhill rules, some brands are experimenting with 29″ and "mullet" 29″ cross 27.5″ downhill bikes. Tires are usually 2.5-2.6″ wide, plus tires are 2.8-3.0″. Plus tires are only used in recreational riding, not competition.

Materials

Downhill bikes are typically made of steel, aluminum or carbon fiber. Some manufacturers have started using 3d printed "lugs" for a more personalized geometry.

See also

References

  1. 1 2 Philip Foster (Jul 21, 2011). "What is the difference between a downhill bike and a freeride bike?". LiveStrong. Retrieved 2012-07-13. The downhill mountain bike is equipped with a heavier frame.
  2. 1 2 3 "Specialized Demo0 Carbon DH mountain bike unveiled - full specs, geometry & more". BikeBoardMedia, Inc. June 2, 2012. Retrieved 2012-07-13. Running Rockshox Boxxer forks with 8″ and their dual seat stay rear triangle with 8″ of rear wheel travel. Head tube angle = 64º. Wheelbase = 1,171–1,208 millimetres (46.1–47.6 in).
  3. ↑ "Cane Creek unveils Angleset: adjustable angle headsets". BikeBoard Media Inc. June 17, 2010. Retrieved 2012-07-13. Today Cane Creek has officially unveiled their all-new Angleset, an adjustable angle headset that lets you fine-tune your bike's handling.
  4. ↑ "Headset Standards". Park Tool Co. Retrieved 2012-07-13. The Onepointfive Standard® uses a 1.5-inch diameter (38.1mm) steering column.
  5. ↑ David Streever. "Mtb Brakes 101". The Adventure Junkies. Retrieved 2017-05-31. the heavy 203 mm rotors are best for downhill
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