• Tandem bicycles and tandem components are fairly uncommon in the world of cycling.bicycle image by Einar Bog from Fotolia.com
  
  Tandem bicycles have several special needs to support the weight of two riders, according to the tandem experts at Peter White Cycles. Usually these special needs are met through heavier, more durable components; however, tandems have three main areas where components must have special, tandem-only designs. Most tandem-only components, such as hubs and brakes, are merely stronger versions of current or out-of-date technology, but cranks, chain tensioning systems and stoker stems are all tandem-specific.
  
  

Tandem Cranks

• Tandem cranks typically work in sync with the rear rider's crank, having a chain ring on the left crank that is attached with a sync chain to the front rider's left crank chain ring. The stoker (rear rider) right crank appears much as traditional cranks do. Pilot (front rider) right cranks are bare, without chain rings, the way most traditional left cranks are. The chain connecting the two cranks ensures that pilots and stokers pedal an even pace with each other.
  
  

Tandem Chain Tension Systems

• Because of the additional syncing chain, tandems need a chain tensioning device. Most current tandems utilize an eccentric bottom bracket for chain tension. Eccentric bottom brackets are simply cylinders within cylinders, according to noted bicycle expert Sheldon Brown. The outer cylinder is mounted in an oversize adjustable eccentric bottom bracket shell. The inner cylinder sits off-center of the outer cylinder, and adjusts chain tension as the outer cylinder is rotated.
  
  

Tandem Stoker Handlebar Stems

• Most bicycle handlebar stems are designed to mount in or clamp on the steer tube of a bicycle fork extending away from the rider. Stoker stems mount to the pilot’s seat-post and extend toward the stoker. Stoker stems are available in a variety of clamp sizes, as seat-posts are, and are typically length-adjustable for stoker fit and comfort. Stoker stems commonly hold bullhorn-style handlebars, though many stokers use flat or drop-style bars as well.