Two things worked in concert with each other to make motorcycles look so large today:
- The engine grew bigger and bigger, so the motorcycle grew bigger to hold the engine and support the weight. As the motorcycle grew heavier, the wheels and tires got bigger and stronger to support the weight, as did the brakes, the frame, etc. The fuel tank also expanded to give the larger engine the fuel it needs.
- With growing engine sizes, motorcycles became much faster and could travel much longer distances. Higher speeds meant the addition of a transmission. Rider comfort in the form of bigger tires, suspension systems, seats and so on were added to make the ride better. Additional speed also makes the tires more important for performance, so the tires got wider.
This motorcycle is not a Harley -- it is a Harley-like custom motorcycle that strips a modern motorcycle down to its bare essentials. For example, this motorcycle has an engine and a transmission:
In this case the engine is an 88 cubic-inch (1,450 cc), two-cylinder engine. The cylinders are arranged in a V configuration with a 45-degree angle to the V. The engine uses dry sump lubrication, and the external tank for the oil mounts above the transmission. Exhaust is simply a pair of stainless steel pipes connected to the exhaust port of each cylinder. There is no muffler or catalytic converter of any kind.
The transmission sits just behind the engine. It is a 6-speed sequential manual gearbox. The engine transmits its power from the crankshaft to the transmission through a primary drive. The power then moves from the transmission to the rear wheel through the final drive, which in this case is a chain as seen in this photo:
You can also see the rear disk brake, as well as the back portion of the frame. In the above photo, as well as the photo below, it's obvious that motorcycle frames can be extremely simple.