Since I am a big fan of custom recumbents, I wanted to share some pictures and considerations of building your own recumbent. How does it differ from a normal bike? Do you need a custom fairing? What seat position should you choose? Here are some considerations:
One of the most striking characteristics of most recumbent is the use of small wheels. Small wheels are used primarily to reduce the overall length of long wheelbase designs, and to improve heel clearances on short wheelbase designs. But it turns out there are other advantages to small wheel designs. Road racers using 700C rims are quick to point out that smaller rims have higher rolling resistance. At around 20 mph, aero drag becomes a bigger factor than rolling resistance. So small wheels contribute to higher top speeds. Smaller wheels are also lighter weight, and lighter wheels make a bike accelerate faster.
Until recently, it was necessary to use low quality ‘kiddie bike’ tires on the rims commonly used on recumbents. Recumbents are now being manufactured in sufficient quantities that tire makers have started making high quality tires in suitable sizes for recumbents.
Most recumbent designs use a small front, and a large rear wheel. Since the rear wheel is behind the rider’s body, aerodynamic drag is not as much of a concern. The large wheel allows the use of conventional gearing; otherwise very large chainrings are required to compensate for a small wheel while still allowing speeds on level ground greater than 18-20 mph.
Mid-drive solves two other problems at the same time. First, controlling the long drive chain used on a recumbent usually requires an idler; the mid-drive functions as an idler. Second, designing a performance recumbent requires a very wide gearing range. Building a wide range 21- or 24-speed system results in large steps between gears. The mid-drive system has 35 speeds, so there is a good compromise between range and step. Mid-drive allows fully indexed shifting over all 35 combinations of gearing, too. There is no chance of chain jam caused by ‘illegal’ front and rear combos since the each derailleurs controls a separate chain.
While under-seat steering (USS) is indeed very comfortable, it results in more frontal surface area. Above-seat steering (ASS) to make our bikes more aerodynamic. And if you add a windshield or a full body, it can be narrower than the windshield for a similar USS bike.
Some designers believe that a solid seat back is best for power transfer. Some use a breathable mesh back rest with a solid foam saddle. Especially in hot climates, an all mesh design tends to be the most practical and comfortable for extended riding.
There are two reasons to put one of these onto your bike. 1. It will make you faster because your aerodynamic drag will be 10-20% lower. 2. Weather protection. It will keep you warmer in cold weather. It will keep you drier when it rains. (This assumes you will put fenders on, too!)