Tandem bicycle

The tandem bicycle or twin is a form of bicycle (occasionally, a tricycle) designed to be ridden by more than one person. The term tandem refers to the seating arrangement (fore to aft, not side-by-side) instead of the number of riders.

History

Patents related to tandem bicycles date from the late 1800s.cite web
url = http://patentpending.blogs.com/patent_pending_blog/2006/05/tandem_bike_189.html
title = Patent Pending Blog: Tandem Bike, 1891
accessdate = 2007-03-08] Modern technology has improved component and frame designs, and many tandems are as well-built as modern high-end road and off-road bikes.

Performance

While a tandem has double the pedalling power with only slightly more frictional loss in the drivetrain, it has about the same wind resistance as a single bike. High performance tandems may weigh less than twice as much as a single bike, so the power to weight ratio can be slightly better than that of a single bike and rider. Tandems can reach relatively high speeds, especially downhill and on flat to rolling terrain. They are not necessarily slower on climbs, but are perceived as such, in part due the need for a high level of coordination between the riders, especially if the physical abilities of the two riders are very different, requiring a compromise on cadence.

Terminology

On conventional tandems, the front rider steers the bicycle and is known as the "captain", "pilot", or "steersman"; the rear rider only pedals and is known as the "stoker", "navigator", or "rear admiral". On most tandems the two sets of cranks are mechanically linked by a timing chain and turn at the same rate.

Uses

Tandem bicycles are often used in competitions such as the Paralympics with blind and visually impaired cyclists riding as stokers with fully-sighted captains.

Variations

More than two riders

Tandems can have more than 2 riders — tandem refers to the arrangement of the riders one behind the other rather than the number of riders. Bicycles for three, four, or five riders are referred to as "triples" or "triplets", "quads" or "quadruplets", and "quints" or "quintuplets" respectively. One such familiar to UK TV viewers was the "trandem" ridden by The Goodies. Originally a 2-man tandem with an extra "dummy" seat attached, a full 3-man version was built for them by Raleigh.

Independent pedaling

Some designs such as the DaVinci allow independent pedaling through the use of multiple freewheels. In another design, the rear rider steers and propels the rear wheel with pedals, and the front rider propels the front wheel with both hands and feet. [cite web
title = SKYWHEEL
url = http://www.skywheel.kr/]

eating arrangements

Tandems come with both upright and recumbent seating.

The [http://www.bilenky.com/viewpnt.html Bilenky ViewPoint] (originally the Opus Counterpoint) is a semi-recumbent tandem steered by the captain who sits upright in the rear, while the stoker rides in a recumbent position in the front. The [http://www.angletechcycles.com/bikes/tandems/ Angletech Harmony] is another semi-recumbent tandem. (Both also feature independent stoker pedaling.)

The "Buddy Bike" is designed to allow a child to sit on the front saddle with an adult on the rear saddle and steering with extra long handlebars. [cite web
title = Buddy Bike
url = http://www.buddybike.com/
accessdate = 2007-10-19]

Tricycles

Tandems are also available as tricycles; the conventional tandem trike has a small but devoted following in the United Kingdom, and is available in one-wheel and two-wheel drive designs. Recumbent tandem tricycles are also gaining popularity throughout the world [http://www.skywheel.kr/] .

Couplers

It is possible to add couplers either during manufacturing or as a retrofit so that the frame can be disassembled into smaller pieces to facilitate packing and travel. Santana manufactures a "triplet (or quad) that can be transformed into a tandem by simply removing the center section of the frame."cite web
url = http://santanatandem.com/Bikes/Family07.html
title = When two seats are not enough
accessdate = 2007-10-19]

Tandem specific components

Tandems are subjected to unique stresses caused by additional riders and weight requiring solutions specific to tandem construction. The phrase "Tandem Specific" was popularized by its use in Santana tandem catalogs during the 1990s.

Drive train

To transfer power from all pedals to the rear wheel requires a drive train. Typically, the front most crankset turns a timing chain, which in turn connects to the rear crankset, which transfers this power to the drive chain that connects to the rear wheel. This configuration is called crossover rear drive, and involves the rear crankset turning two chains.

The second most popular solution, due to being able to retrofit a singles bike into a tandem is called single side rear drive. The front crankset drives a timing chain which connects to the rear crankset. The rear crankset has another chain ring that connects a second chain, the drive chain to the rear wheel.

The least popular solution is to run a drive chain from the front crankset, to the rear wheel, then a timing chain from the front crankset to the rear crankset. It is least popular because it requires considerably more chain then either other setup. Such a setup is called crossover front drive.

A unique solution to the requirement that the captain and stoker having to both padel at the same time was when one bike maker added a jack shaft plus TWO freehubs, thus allowing one or the other to coast while the other continued to pedal. This also allowed the riders to select different crank postions (Inphase, IP or Out-Of-Phases OOP) while pedalling together.

Crankset

The front crankset typically has only one chain ring. The rear crankset typically has many chain rings, sometimes on both sides. On a tandem where the pedaling is designed to be in sync, both cranksets will use a chain ring for the timing chain of the same size. The drive chain chain rings can be single gear or use a derailleur.

To maintain the necessary tension on the timing chain, many tandems use an eccentric that is placed in the captain's bottom bracket shell. An alternate solution is to implement a pully, or idler, on the bottom of the timing chain to take up slack. Idlers add friction and a potential point of failure to the drive train.

Handle bars and stem

Stoker handlebars are typically connected to a stoker stem that is clamped around the captain's seatpost. The stoker handlebars are typically bull horns or very wide drop bars with "stoker pegs" instead of brake levers.

Wheels

Because of the extra weight and stresses, tandem wheels may use a higher spoke count, sturdier rims, higher pressure tires, a stronger freewheel, dishless spoke configuration, or asymmetric wheels. Tandems wear out rear wheels faster than front wheels; therefore, they may use non-symmetrical wheel setups, such as more spokes or a sturdier rim on the rear wheel.

The dish of a wheel measures the amount of asymmetry between the rim and the hub flanges. To accommodate a large cassette, more space is needed on the drive side of the axle; this increases the complexity of manufacturing and truing the wheel. Tandem rear wheels tend to run a wider hub/axle to allow the right-side hub flange to be further right of wheel centre and thus reduce the total dish of the wheel. Some modern tandems use a 160mm wide axle which allows a wheel that is completely "dishless" (i.e. symmetric). Others use shorter axles (often 145mm wide) thereby trading a little decrease in the strength of the wheel for the advantage of a similar decrease in the bending moment of the axle spindle. Rear hubs may also be threaded on the left side to allow the use of an drum brake.

Brakes

The Arai drum brake is used during long down hill descents where a typical rim brake (and many disc brakes) would overheat and fail (rim brakes melt tires and disc brakes warp rotors, boiling fluid, or melt parts). The drum of the brake screws onto the left side of the tandem hub, which must be threaded for the drum. The shoe plate slips over the axle and a small reaction arm from the shoe plate engages with the bicycle frame to prevent the plate from turning. The tension on the drum brake is typically controlled using a friction shifter like a BARCON or similar. The brake is designed to be left on during the descent to maintain a steady speed and the standard brakes can be used in addition as necessary.

Tandem specific riding techniques

;Stoker starts clipped in while captain holds bike uprightFor those who can get accustomed to the stoker always being clipped in, the distinct advantage to this technique will become obvious when trying to start at the foot of a bridge or on a hill. If the tandem team does not practice this, then they often reserve this type of start for when they are faced with a bridge or hill. This technique allows the stoker to apply continuous power as the captain steadies the bike during the initial take off. This reduces the risk of the bike toppling over due to starting on an incline. The stoker will continue to pedal as the captain attempts to get the foot used for steadying the bike clipped into the pedal.

;In-phase cranks vs out-of-phase cranksIn-phase (IP) versus out-of-phase (OOP) is a choice that can be made by the captain and stoker based on their perceived experience of riding the tandem. In-phase simply means that the cranks are setup so that both the captain and the stoker cranks are in the same clock position at the same time. Users of the traditional "two banger" approach say coordination between riders is better with the cranks in phase.

Out-of-phase has the potential for a wide range of variation. Some tandem riders arrange their cranks so that they are 90 degrees out of phase, the "4 banger arrangement". In practice, as noted on Tandem at Hobbes postings, OOP setups range from a mere two-tooth difference to a full 90-degree OOP setup. Generally, OOP provides the greatest benefits to the tandem team that has disparate leg-strength. When the tandem is setup IP it is possible, and often happens, that the stronger rider literally drops the pedals out from beneith the feet of the weaker rider. That gives the sense that the other person is "not pedaling." Using OOP makes a significant difference in gearing choice as each rider has the full mass of the tandem in their power stroke, so lower gears are preferred. However, using OOP can help develop leg strength for the very same reason. Some argue that this produces a smoother power stroke, or that it reduces stress on the drive train because the point of maximum power is reduced to roughly half and distributed over the chain rings.

In the end it is a matter of the preferences of the team. There is not an absolute right or wrong in this area, only what works best for a particular team.

Tandem bicycle manufacturers

Since the market for tandem bicycles is significantly smaller than the market for single bikes, there are far fewer tandem bicycle manufacturers than single-bicycle manufacturers. There are a few builders who specialize in tandems, as well as single-bike makers who offer tandem models. Current tandem bicycle manufacturers include:

*Bohemian Bicycles
*Cannondale Bicycle Corporation
* [http://www.co-motion.com Co-Motion Cycles]
*KHS Bicycles
* [http://www.santanatandem.com Santana Cycles]
*Torker
*Trek Bicycles

See also

* Cycle rickshaw
* Bicycle trailer
* Sociable
* Quadricycle
* Trailer bike
* Tricycle
* Bicycle Built for Two

References

External links

* [http://www.tandem-club.org.uk The Tandem Club] — the original tandem club, UK-based with Dutch, other European and international members
* [http://www.tandemclub.org The Tandem Club of America] — a U.S.-based club
* [http://www.visitbishopscastle.org.uk/events/tandem.htm The Bishops Castle Tandem Triathlon]