Downhill bike
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- Downhill Mountain Bikes typically have 8 or more inches (200 mm) of suspension travel. They are built as light as possible for racing and range from 45-35 lbs. They are very strong, and due to the typically large, high gears and long, soft travel, are suitable only for riding down dedicated downhill trails and race courses. The suspension is set to sag around 30% front and 50% rear of full travel, creating ample traction around bumpy corners. The head angle is often as slack as 64 degrees. Competition downhill mountain bike racing is where most mountain bike technology is innovated, as most bike manufacturers sponsor a number of riders. Downhill biking is just as it sounds, downhill. Most riders who ride exclusively downhill do so in competitions or ride almost exclusively on lift accessed terrain. Due to the high speed nature of downhill riding most bikes only have one chain ring, a large bash guard and a chain guide. Downhill mountain biking is the most high profile category of competition biking.
- Trials Mountain Bikes are set up very specifically for the purpose of bicycle trials. They typically have no suspension at all, though some still make use of some form of it. Competition rules require bikes to have multiple gears for competition, but most riders never use their shifters. Many non-competitive riders run single-speed, choosing a fairly low-speed, high-torque gear. Most modern trials bikes have no seat at all, as the rider spends all of his time out of the saddle. These bikes are significantly lighter than almost all other mountain bikes, ranging from 15 to 25 pounds. This makes maneuvering the bike much easier.
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[edit] Tire sizes
Most mountain bikes use 26 in (559 mm) wheels, though some models offer 24 or 29 in (520 or 622 mm) wheels(this size is for road/hybrid bikes only not mountain bikes).Inch-sizes for bicycle wheels are not precise measurements: a 29 inch wheel is actually a 700c wheel, which has a 622 mm (24.48 inch) bead seat diameter. 700c is an archaic designation that persists because of its early popularity, though the diameter is 700 of no actual unit of measurement. In some countries, mainly in Continental Europe, 700c wheels are commonly called 28 inch wheels, nevertheless these wheels are equivalent to 29 inch wheels in the English speaking countries.
24 inch wheels are used for Dirt Jumping bikes and sometimes on freeride bikes, rear wheel only, as this makes the bike more maneuverable. 29 inch wheels were once used for only Cross Country purposes, but are now becoming more commonplace in other disciplines of Mountain Biking, and are predicted to be the choice wheel size on Downhill Bikes within a few years by some.
Wheels come in a variety of widths, ranging from standard rims suitable for use with tires in the 26 in x 1.90 in to 2.10 in (559 x 48 to 53 mm) size, to 2.35 and 3.00 in (60 and 76 mm) widths popular with freeride and downhill bicycles.
[edit] Future technology
The first gearbox downhill bike was made and raced by Alex Morgan of bcd bcdracing.comIt is was a carbon fiber frame with two chains. The first chain goes from the cranks to a 7 speed shimano nexus hub. From there the ratio is changed. Then the second chain to drive the rear wheel. The design that Alex Morgan came up with on this bike is still used today. Image:Nicolai-gbox-bike.jpg
Frame mounted gearboxes (generally hub gears adapted to fit) are starting to make an appearance in ultra high end mountain bikes. With the gearing system protected from the elements and from impacts and the weight of the bike held low and central these offer significant advantages over conventional gear systems, particularly for extreme use. These internally geared bicycles are often also referred to as three-speed bicycles.
Nicolai is currently one of the few manufacturers of internal gearbox bikes but other companies such as GT and Alutech have bikes near production. Nicolai use a 'standard' mounting for the gearbox called the G-Boxx, which has also appeared on prototypes from Evil Bikes and Alutech.
The German company of Rohloff also manufactures and supplies a range of internal gearboxes (called the 'SpeedHub') to several bicycle manufacturers and initially also supplied Nicolai. It has since been standardized into the " G-Boxx" This system uses a separate hub above the crankshaft and needs a second set of chains. This gives revolutionary smooth shifting when compared to any external derailleur currently made. The system is also maintenance free and incredibly tough. The main disadvantages are weight and price. Contrary to popular belief the Rohloff 14 speed hub has a gearing range equal to that of a standard 9x3(27 speed) derailleur drivetrain. Additionally the gears are evenly spaced, unlike a standard derailleur systems where the jump between gears can be inconsistent depending upon the front sprocket. The increased weight of the rear wheel can raise some complaints; the new frame-mounted designs eliminate this problem by moving the weight into the centre of the bicycle. Note that this does not imply that hub gears are excessively heavy: they typically weigh only about one pound more than traditional derailleur setups.
Several companies are working on derailleur based frame mounted transmissions, but the benefits of these are subject to much dispute. Mountain Bike Action magazine reported in October 2004 that Hayes would manufacture and sell a transmission based on the PeteSpeed design. This appears to be targeted at downhill and freeride bikes, where it has the advantage that there is no rear derailleur that can be damaged by contact with rocks and other obstacles. However, the weight compared with a traditional triple chainring and rear derailleur setup would seem to make it less suitable for cross-country riding.
Soon to be available is a rear hub with a self contained CVT (Continuously Variable Transmission) within the rear hub of the bicycle. The external appearance is that of a single-speed bicycle, with one chain ring, one sprocket and a chain tensioner. Their primary disadvantage is weight, but their placement on the bicycle ensures that they will not be damaged by trail obstacles while riding. If this drivetrain design is improved upon in the future, it opens up the possibilities of bikes with motocross style concentric chain rings and suspension pivot points, thereby improving the durability of the bike while eliminating pedal bob.
[edit] See also
- UCI Mountain Bike & Trials World Championships
- Mountain unicycling
- Bike trials riding
- National Off-Road Bicycle Association (NORBA)
- Dirt Jumping
[edit] External links
| Wikimedia Commons has media related to: |
- IMBA (International Mountain Biking Association)
- "A Brief History of the Mountain Bike" by Jobst Brandt
- Mountain Bike Roots - photos and race results from 1980's events
- MTBrider - Northern Ireland's mountain bike community
