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Recumbent DesignSome thoughts that form the basis for Rotator's designs |
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Wheel sizesOne of the most striking characteristics of most recumbents 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 ERTO 406 (20") 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. As a result, Rotator is using the ERTO 406 rim size as a standard on its bikes. 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. We solved the gearing problem by developing a mid-drive system with two freewheels. Mid-drive system
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 we believe under-seat steering (USS) is indeed very comfortable, it
results in more frontal surface area. We use 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.
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Rotator Recumbent Bicycles 3200 Dutton, Suite 215 Santa Rosa, California 95407 707-591-0915 FAX: 707-591-0916 Email: sales@rotatorrecumbent.com |
Steering
position.