The Megola is a German motorbike that was manufactured between 1921 and 1925. It was available in two variations: touring and sporting. The Megola had two gasoline tanks, a fuel gauge, a tachometer, an ammeter, and a hand-controlled butterfly valve for throttle control. This antique motorbike was remarkable in that it had a 640cc radial engine positioned within the front wheel structure. The engine had side-mounted valves and five cylinders that rotated at six times the wheel speed around the front axle. Despite its adaptability, this engine lacked both a transmission and a clutch. This Megola engine produced a meager 14bhp when supplied straight to the wheel. ¹⁾

Georges Roy designed it from 1928 to 1934. The bike had a pressed-steel structure that was more like to a car than to other two-wheel machines. The framework was excellent because it allowed multiple components to work together as a single entity. Roy's motorcycle design eliminated difficult welding processes by riveting steel panels together into a monocoque chassis that served as the bike's bodywork and frame. The steel panels created a semi-circular spar arrangement that connected the steering head to the bike's robust rear axle, enclosing the rear tire in a sleek steel fender. ²⁾

Carl Neracher invented the Ner-A-Car in 1918, which became legendary as the most successful hub-center steering motorcycle ever made. Carl created this motorbike with unique characteristics such as an all-encompassing bodywork, a low-slung perimeter frame chassis, a feet-forward riding position, hub-center steering, and a friction-drive transmission powered by the engine's flywheel. ³⁾

Piaggio, an Italian manufacturer, first offered the MP3 as a tilting three-wheel scooter in 2016. Riders may stop and park the MP3 on a level, irregular, or side-sloping surface using the three-wheel arrangement rather than the standard center or kickstands. An alloy parallelogram connects the front suspension of the single-sided trailing arm to the central steering arm. ⁴⁾

The Imme had interchangeable wheels, long-travel suspension, friction dampers, a 3-speed transmission, a tubular swingarm that doubled as an exhaust pipe, and a crankshaft that was suspended on only one side. This motorbike was powered by a 99cc two-stroke single-cylinder piston-ported engine capable of producing 4.4bhp at 5800rpm. ⁵⁾

The Quasar is a semi-enclosed motorcycle that uses the same feet forward design as the previous Ner-A-Car. This motorcycle was groundbreaking in that it shifted the rider's position from on top and straddling to inside and sat down. The Quasar has a roofed interior, a laminated glass windscreen, car-style wipers, and a heater. ⁶⁾

In 1958, Charlie Fehn designed the Nethercutt Trail-Breaker, a two-wheel-drive motorbike. Rokon Inc. purchased the production rights in 1964 and renamed it the Rokon Trail-Breaker. The motorbike is well-known for its use of a unique mixture of chain, belt, and shaft drives linked with gearboxes to power both the rear and front wheels. For long-distance rides, the motorcycle's hollow wheels can contain 2.5 gallons of water or gasoline. The earlier Trail-Breaker had a 134cc two-stroke engine, whereas the new ones featured either a 6bhp Honda or a 6bhp Kohler engine. ⁷⁾

Alfred Scott transformed the two-stroke engine from a low-performance utility to a high-performance engine that shaped the motorcycle industry. Scott's motorbikes had liquid cooling, parallel twin cylinders, a 180-degree crank, a three-port intake system, and a big internal flywheel. Furthermore, the Scott motorbikes were among the first to use a kickstarter rather than pedals, as well as rotary disc intake valves. ⁸⁾