Adding a self-built aerodynamic outer shell to a brand new Honda Innova 125i big-wheeled, step through scooter has resulted in its already pretty impressive fuel efficiency being improved considerably. Experienced Dutch cycle designer Allert Jacobs has spent the last couple of years designing, building and tweaking his machine before hitting the road recently for the all important road test.

After designing an aerodynamic, recumbent pedal-powered three-wheeler, Jacobs started to think about the possibility of moving onto bigger and more powerful vehicles. Considering the rules and regulations involved in building a roadworthy car to be too restrictive, he set his sights on a motorbike.

Streamlining performance motorcycles is by no means new. Sport machines began getting some pretty impressive results from enclosed fairings before the Fédération Internationale de Motocyclisme put the brakes on full enclosure fairings for sport motorcycles in the 1950s due to safety concerns.

Since then, work by (amongst others) Craig Vetter has shown that not only does streamlining provide gains in the speed department but also results in some impressive fuel savings. Vetter has, in fact, just recently managed to persuade the Fédération to lift its ban for electric motorbikes, opening the floodgates for electric fairing enhancements for future performance riders.

Aerodynamics is a real drag

Forward movement is of course met with resistance to that movement, from the air and from any surface an object happens to be in contact with. Most of the resistance encountered on a motorcycle however is aerodynamic. Any motorcyclist who has tucked down close to the bike will know that reducing drag results in a speed boost without the need for increased throttle. Jacobs calculated that at 55mph, a naked motorbike is likely to suffer 90% of its resistance due to aerodynamic drag.

The ideal solution for a fuel efficient motorbike would be an electrically-powered one, but Jacobs considered limited range to be problematic so he opted for the small and light engined Honda Innova 125i, which was first made available to Europeans in 2006 and was intended to replace the popular Super Cub. The Innova is already highly regarded for efficiency, Honda UK claiming it gives: "a robust 46 miles of operation on a single liter of fuel (measured at an operating urban speed of 33mph)".

Filling its 3.7 liter fuel tank got Jacobs around 140 miles to the gallon (mpg) during the initial run in period required for a new vehicle. When he started to increase throttle activity somewhat, the scooter still offered between 107 and 122mpg. Inspired by the work of the likes of Vetter, Jacobs decided to aim for 235mpg fuel efficiency for his creation.

Trimming the fat

In the Winter of 2007 Jacobs started his project by stripping away the Innova's body work and seating. He then installed footrests above the front wheel to cater for a recumbent riding position, threw in some seating and attached a nosecone. An early evaluation showed that even these modest modifications had increased the bike's top speed and fuel efficiency but there was still much more to be done.

As a result of instability issues, he was forced enclose the front wheel within the streamlining casing instead of underneath the nosecone and modify the riding position so that his feet moved down to rest at each side of the wheel when in motion. The latter half of 2008 was spent taking the design suggestions offered by a 1:5 scale model and creating a full size template from PU foam.

2009 dawned and with it the creation of the mould for the final streamlined casing. Modifications were made to the steering and the exhaust was lowered so that it sat outside of the casing. Getting in and out of the casing was made possible by slicing it down the middle and attaching the front end to a rail which extended it forward by 18 inches. Rubber cones and trips ensured a snug fit when in cruising position and an open bottom design catered for stable ground footing when at rest. The lights were also wired up and tested.

Hit the road, Jack

With everything in place and working it was time for the all important road test. Jacobs climbed into the 319 pound vehicle (88 pounds heavier than the original scooter) and set off for a 160 mile stretch of open road. His creation managed to achieve an amazing 214mpg at around 55mph with good conditions and only a 25mph wind.

Jacobs suspects that some fine tuning will see his vehicle reach that target fuel efficiency of 235mpg but as of writing, the poor weather being what it is, he has been putting his time to good use by pimping his ride, adding reflective striping and other embellishments. As the weather improves, his work in progress may yet see his target achieved and perhaps even exceeded.