Obviously, you need a bicycle, though there are those who prefer three wheels, for reasons I'm not entirely clear about--the advantages seem mainly to come when the trike is stopped, and I don't ride fast enough to be able to let that happen for long.
Bicycles may be regular or recumbent. The history of the bicycle is a long old story, but it's enough to know that the early designers were heavily influenced by the horse culture prevailing at the time. You straddle a horse, so you straddle a bicycle, right? Invent a chain and some gears to enable the drive wheel to be a reasonable size and, voila, there you have it, the diamond-framed safety bicycle, still the dominant model today.
If you were starting from first principles you wouldn't build a bike like that for a couple of reasons. First, most of the work your legs do against the pedals is spent on pushing the air aside. One way to deal with this is, as we have already suggested, is to ride with cyclists of a similar velocity; another would be to tilt the long axis of the human body through 90 degrees to present a lower cross-sectional area to the air. This position, supine, feet first, is known as the recumbent position, and it works very well. All of the human-powered vehicle records are currently set with vehicles that are variants on this theme, and such bicycles are becoming widely available commercially. The innovation has been slow to develop because it was banned from competition by the conservative cycle racing authorities in the 1930s, divorcing it from competition and making it the province of nerdy record breakers.
Second, the upright position has a number of ergonomic disadvantages. The body weight is transmitted to the bike through three points: the wrists, the saddle, and the feet. With the right shoes the feet can look after themselves, but your wrists and your bum just weren't designed for hour after hour of this thing, and problems can develop. Numbness, tingling and pain in the shoulders, neck, wrists and hands are routine for long distance cyclists. Taking frequent "butt breaks" (rising from the saddle to relieve the pressure on the perineum) is also essential if you're going to keep the skin of your backside free from boils and chafing, but this puts even greater demands on your stamina and upper body strength.
The only down side of the recumbent position is acceleration up hill. Because it is not possible to rise from the saddle, you can't manipulate much upper body strength into the riding action, which means that hills have to be taken at a steady pace. Still, that's what your gears are for: just choose a low one, and twiddle it up. As the guru says: "Think leg speed, not road speed." Fast legs are very important for riding a bike: if you want to transmit more energy to the road, it's a lot easier to give the cranks another turn than it is to increase the force you apply to the pedals. And so you will find it is with the recumbent up the hills. PBP is fairly hilly throughout its course, but there is nothing so devastatingly steep that you have to get off and walk.
The machine I used for the long events, HP Velotechnik's Street Machine, has not only a reclined riding position, but also full suspension, was a very comfy beast indeed. On the ultimate test: the Paris-Brest-Paris, which I completed in 85 hours, I had very little discomfort in any part of my body. In contrast, the painful hunched postures of some of the riders who had completed the PBP on regular bikes, with strapping and dressings protruding from their shorts was awful to behold. Cycling is good fun, but you don't want to pay too high a price for it in your nether regions.
On the shorter events, provided it is mechanically reliable and fits, the kind of bike you ride doesn't really matter too much. Lighter is obviously better, high pressure tyres that minimise rolling resistance are useful, as are handlebars that permit a variety of hand positions. On the whole you want lower gear ratios than for road racing.
©Douglas Carnall 1999