Okay guys and gals! Quiet down now and get out your notebooks. It's time for class to begin! Today I will discuss the relationship between the chassis and the engine in terms of geometry. You say, "What?" Yes, I said, "chassis and engine"! Let me explain.
The bicycle can be thought of as a rolling chassis, to borrow from automobile terminology. A rolling chassis is everything you need to get down the road except the means of propulsion. In the case of an automobile, that's the engine. On a bicycle, the person riding is the engine! The way you mount the engine on the chassis is critical to the performance of the parts as a whole.
A car has what are called engine mounts to connect the engine to the chassis. Extreme care is given to the placement of the engine in the car to realize the intended handling characteristics of each automobile design. The same is true for bicycles. The engine mounts for a bicycle are the pedals, saddle, and the handlebars. Where these points fall in space will determine not only how the bicycle will handle but also how the engine will perform. It is therefore critically important to make sure that the geometry of the engine mounts not only accomodate the intended handling characteristics of the bicycle, but also keep the engine comfortable and efficient. Sound complicated? Well, it is!
Given the fact that all humans are uniquely gifted and individual in design details, it is easy to see that production bicycles are somewhat compromised when it comes to making all the contact points achieve the goals of efficiancy and comfort. It's a "one size fits most" solution, with a degree of tunability mixed in. In the next installment, we will see what the contact points do to the engine and how moving those affects the handling characteristics of bicycles.