Velomobile

Overview

A velomobile is what happens when a recumbent trike is optimized for one variable: aerodynamic drag. Above about 15 km/h, air resistance dominates a cyclist's power budget, and at 40 km/h it consumes nearly all of it. An upright rider presents a drag area (CdA) of 0.3-0.4 m²; the Aerodynamic Shell cuts that to 0.025-0.05 m², an order of magnitude. The practical result is that a rider producing a sustainable 150 W, touring effort on a normal bicycle, good for perhaps 27 km/h, cruises at 40-50 km/h in a velomobile. Commuters routinely log 50-100 km days in them year round, because the shell also keeps off rain, wind and cold.

The shell

The Body Monocoque is the vehicle: a vacuum-infused carbon-aramid skin 1.2-2 mm thick that is simultaneously the fairing and the primary structure, the same logic as an aircraft fuselage. There is no separate frame. Suspension, seat and drivetrain loads enter the skin through bonded Hardpoint Insert fittings and two Foam Bulkhead sandwich panels. The Nose Cone is a separate, replaceable section, since the nose takes every parking scrape and minor collision; the Tail Section tapers the airflow back together and swallows about 50 L of luggage. Each Wheel Well is closely faired because an exposed rotating wheel is one of the worst drag sources on the vehicle. A removable Cockpit Canopy closes the cockpit opening in winter; most riders run open-top in summer for cooling, accepting a few km/h of loss.

Drivetrain

The rider lies in a Seat Assembly reclined to 25-30 degrees on the Seat Mount, pedaling forward against the seat back rather than against body weight. The Crankset sits on a telescoping Bottom-Bracket Boom adjusted to leg length, and uses short 155-165 mm cranks to keep heels clear of the shell and knees out of the airflow opening. From there the Long Drive Chain, roughly 280 links, two and a half ordinary chains, runs the length of the vehicle over two toothed Chain Idler pulleys and through PTFE-lined Chain Tube guides that keep grease off the rider. Gearing is conventional at the back: an 11-34 Cassette and a Rear Derailleur, but with a 50-60 tooth chainring, because the speeds are not conventional. Clipless Pedal retention is effectively mandatory: at recumbent angles a foot that slips off the pedal at 45 km/h goes under the vehicle.

Steering and suspension

Both 406 mm front wheels steer. Inside the cockpit a Steering Tiller between the knees (or twin side-sticks in some designs) moves two Tie Rod links to a Steering Arm on each Steering Knuckle, with Ackermann angles so the inner wheel turns tighter in corners and a light Centering Spring returning the tiller to straight. Steering at 50+ km/h needs almost no input; geometry stability, not rider reflex, keeps the vehicle straight.

Suspension is non-negotiable in a vehicle this fast with 50 mm of ground clearance. Each Front Suspension Corner corner is a small McPherson strut: the wheel rides a sliding Suspension Strut Tube compressed against a Elastomer Spring Stack of urethane pucks giving about 40 mm of travel with inherent damping and zero maintenance. The rear wheel hangs on a single-sided Rear Swingarm sprung by a Rear Elastomer Spring block, single-sided so the wheel can be pulled sideways out of the tail for puncture repair.

Brakes and lights

Both front hubs contain 90 mm Drum Brake units. Drums rather than discs are near-universal in velomobiles: they sit sealed inside the Wheel Well, work identically wet or dry, and their fade limit is acceptable because aerodynamic drag itself retards the vehicle strongly above 50 km/h. The two tiller-mounted Brake Lever units pull the drums through Brake Cable runs, and a Parking Brake Pin latches a lever for parking. Because the rider is sealed inside, hand signals are impossible, so the Lighting System system carries four Turn Indicator flashers along with the LED Headlight and LED Taillight, all fed from a small pack of LiPo Cell cells good for several weeks of commuting per charge.

Performance and limits

The records illustrate what the shell buys. Fully streamlined human-powered vehicles built on the same principles hold the flying 200 m record above 144 km/h; practical commuting velomobiles with luggage and lights are slower but still let an ordinary rider hold speeds that would require a professional's power output on an upright bicycle. The trade-offs are mass (22-32 kg hurts on climbs, where aerodynamics gives nothing back), summer heat load, a 4-5 m turning circle, and price, small-series composite construction puts most velomobiles at the cost of a used car.