Since their weight is also less than double, tandems ought also to go a bit better uphill; but they don’t and this is a source of much debate. The most likely explanation is that you don’t actually get double the power, especially uphill, when each rider tries to move the bike in their own particular way and must instead reach a compromise with their partner. This theory is confirmed by the observation that well-matched riders can go uphill as fast on a tandem.
Pros & Cons
The other big advantage of a tandem is togetherness. Riders of differing strength don’t lose one another, you can keep up the chat – including when the road is too narrow or busy to ride side by side – every mile of the ride and every hill is a joint experience and a joint achievement.
Riders can pool their skills. The steersman, pilot or captain (tandeming has its own rich vein of cycling jargon) operates the controls whilst the stoker, navigator or whatever hands out food and reads the map. Tandems are the solution when a cycling companion has limited eyesight, difficulty with balance or getting on and off the bike. They are also perfect - when adapted or made for this purpose - for taking young children cycling on longer rides and busier roads than they could manage solo.
Aside from hill-climbing, the disadvantages of a tandem revolve around the size of the machine and the higher forces that must be borne by components that are little different – if at all – from those of a solo bicycle (a 'half-bike' in tandem parlance).
Tandems are more difficult to manoeuvre, to transport and store. They are expensive to buy and maintain, although no more so than two solo bicycles of identical quality. Cheaper tandems come with solo wheels and they’ll do if both riders, particularly the stoker, are lightly built.
However, it’s worth having a special tandem wheel with 40 or 48 spokes, at least at the back. A 'drag brake' (a third brake, usually at the hub, that can be held on, usually by the stoker, on long or very steep descents) relieves the main front and rear brakes, which are invariably the same as on a solo.
Tandem touring has the 'quart into a pint-pot' challenge of two people’s stuff and only one set of places to put it. That shouldn’t be a problem unless you’re camping, in which case a trailer may be needed.
Riding a tandem is not so difficult. The pilot should practise on their own first, to become familiar with the gears, brakes, handling and length of the machine. Beware though, that the rear wheel of an 'empty tandem' skids at the lightest touch of the rear brake.
A tandem is easy to ride provided the stoker keeps relaxed. Tense up and the pilot cannot balance the bike without moving the stoker’s whole body from side to side. That’s hard to do. It’s also hard for a novice stoker to relax. It often helps the learning process if the stoker holds the pilot’s waist instead of the handlebars.
Starting and stopping is the trickiest bit of riding a tandem.
The usual drill is for the pilot first to straddle the frame, both feet on the ground, hands gripping the brakes and top-tube gripped between the thighs. And if they want to avoid getting a pedal in the shin during what comes next, it’ll help if they put the right one at 9 o’clock (viewed from the left), ready for starting off.
Then the stoker throws a leg over the rear saddle, places their right foot on that right pedal, lifts their weight into the saddle (pilot: remember to hold those brakes) and also places their left foot. The pilot now balances the stoker’s weight, places their right foot and prepares for the off. When ready they let go the brakes, jumps onto that right pedal and into the saddle – just like they’d start on a solo – whilst calling “GO” or some other agreed signal, at which the stoker also turns on the power.
With the stoker able to pedal with full power from the word go, the tandem is under way even more promptly than a solo, minimising any start-up wobbles. When halted, the stoker should keep their feet on the pedals, since that makes it easier for the pilot to balance their own weight and ensures a quick getaway.
An alternative procedure, useful for short stokers on tall tandems, is to begin with the left pedal at bottom (6 o’clock) so the stoker can use it as a mounting step. Then roll the tandem forward a little, to bring the right pedal into position for maximum thrust at take-off.
To dismount reverse the starting procedure
Pilot holds the tandem up whilst stoker gets down and off. Pilots beware: if the stoker remains near the tandem your usual leg over saddle dismount may deliver a nasty kick to their head! The width of the rear handlebar also renders this manoeuvre more difficult – it’s all too easy to catch a leg and tumble in an embarrassed heap.
Experienced tandem pilots perfect the balletic art of instead kicking one leg over the handlebars, whilst transferring their hold on the handlebar from left hand to right. This enables them to leave the machine in the hands of their semi-dismounted stoker whilst answering a call of … err, photography!
Only the most experienced and co-ordinated tandemists are able to stand on the pedals and dance together up hills (but it looks most impressive if you can) which combined with the aforementioned lack of tandem hill-climbing power, calls for lower bottom gears.
Tandems are however potentially much faster downhill than a solo and can use a higher top. A six to one overall gear range (e.g. 20 to 120 inches) is not unusual on a tandem.
Not every couple gets on well with riding a tandem. The stoker needs to have complete trust in the pilot and if that trust is not there from the outset, it can be difficult for the pilot to earn it, since as I’ve already described: a nervous stoker makes the machine difficult to balance and steer smoothly. (It helps if the stoker has control of the third brake and it’s also a good idea to mount the bike computer on the stoker handlebar – a rear wheel sensor kit will be needed.)
Some cycle hire outlets have a tandem or two available and even if that one isn’t the type of tandem you would ultimately like to own, it’ll do well enough to discover whether tandem riding is for you.
As for buying that tandem: in the 1970s tandems almost disappeared and were kept alive by only a handful of custom builders, mostly British. They’ve since made a comeback and are now mass-produced in many different styles (road, touring, trekking, hybrid and mountain – even some full-suspension) from deluxe down to the middle-market price bracket. Expect to pay about the same as two equivalent quality solos.
Britain can fairly claim to be the cradle of that tandem revival since the Tandem Club was founded here by a group of CTC members in 1971 and, just like CTC, rapidly grew an international membership leading to the foundation of similar clubs in many other countries.
The Tandem Club maintains close ties with CTC (most of their members are also ours) and their website, http://www.tandem-club.org.uk/  holds much useful information on tandems.