Tandem Bicycle Product

Overview

A tandem bicycle carries two riders in line on one frame. The front rider, the captain, steers, brakes, and shifts; the rear rider, the stoker, only pedals. Because two riders produce roughly twice the power of one but present little more frontal area, a tandem is fast on flat roads and descents — and slow uphill, since weight nearly doubles while power does too but climbing speed tracks power-to-weight less favorably with the heavier machine.

The structure that makes this work is the Tandem Frame: about 1.8 m of oversized tubing with two bottom bracket shells (Bottom Bracket Shell) and a Lateral Tube running diagonally from head tube to rear dropout. Without that tube, two riders pedaling out of phase with each other would twist a conventional diamond frame visibly at the bottom brackets.

How it works

The defining mechanism is the Timing Drive. On the left side of the bike, a Timing Chain links a Timing Chainring on the Captain Crankset to an equal-tooth ring on the Stoker Crankset, so both riders turn at exactly the same cadence. Most teams ride in phase (cranks parallel); some offset the rings 90° to smooth the power pulses. Chain tension is set by the Eccentric Bottom Bracket — the captain's bottom bracket sits in an off-center sleeve, and rotating the sleeve in its shell moves the axle fore or aft by up to about 13 mm, taking up chain wear without any sprung tensioner.

Both riders' torque arrives at the stoker crankset, whose right side carries the Drive Chainrings of a conventional Rear Drivetrain. From there a Drive Chain runs to an 11–34T Cassette on the Freehub Body, shifted by a Rear Derailleur and Front Derailleur under control of the captain's Shifter Set. Gearing skews low and wide: a loaded tandem climbs at walking pace and can exceed 80 km/h downhill, so a 50/34 x 11–34 setup spanning roughly 270 % range is common.

Wheels and brakes

Each wheel of the Tandem Wheelset carries close to double a solo bike's load, so a Tandem Rim is drilled for 40–48 spokes and the Spoke Set is laced 3- or 4-cross to wide-flange Tandem Hub shells on oversized axles. Tire widths of 32–40 mm at 5–7 bar spread the load; pinch flats from underinflation are the classic tandem wheel failure.

Braking is the harder physics problem. Kinetic energy scales with mass, so a descending tandem must shed nearly twice the heat of a solo bike through the same two contact patches. The Brake System use four-piston hydraulic Disc Caliper units on 203 mm Disc Rotor discs — the largest common bicycle rotor size. On sustained alpine descents many tandems add a Drag Brake: a hub-mounted drum, set with a friction lever and left lightly applied for minutes at a time, that absorbs steady heat in its large iron drum so the discs stay below fade temperature for actual stops.

The two cockpits

The Captain Cockpit looks like a normal bike cockpit: a Captain Handlebar on a Stem, carrying both Brake Lever units, the shifters, and a Captain Saddle on its Captain Seatpost.

The Stoker Cockpit is the unusual one. The Stoker Handlebar does not connect to the steering at all — its stem clamps around the captain's seatpost, giving the stoker a fixed bracing point. Because the stoker cannot see the road ahead and cannot unweight before a pothole, the Stoker Saddle usually sits on a Stoker Suspension Seatpost with 30–50 mm of spring travel.

Riding technique

A tandem team starts with a procedure: the captain straddles the frame and holds both brakes, the stoker clips in both feet and sets the cranks to the agreed start position, then the captain pushes off and clips in while rolling. Because the timing chain links the cranks rigidly, neither rider can coast or pedal independently; communication ("coasting", "bump", "shifting") substitutes for the feedback a solo rider gets through the pedals. The reinforced Front Fork, with its tandem-rated Fork Blade pair and Headset, gives the captain steering authority over a machine whose 1.7 m-plus wheelbase makes it stable in a straight line and deliberate in corners.