Originally Posted by
Mikefule
Ask the engineers to define "efficiency" then turn it back on them.
There are two ways of defining efficiency: (a) achieving the desired outcome with the minimum use of resources, or (b) achieving the best possible outcome from the resources available.
Clearly a single speed or fixed bike uses considerably fewer resources (money, materials, energy to manufacture, maintenance time) compared to a geared bike.
A little bit of analysis then shows that the definition of "outcome" is crucial. It is not necessarily "top speed" or "average speed" or even anything to do with speed or anything to do with distance covered per unit of energy expended.
If the desired outcome is "enjoyment" then a single speed or fixed can be considerably more efficient than a geared bike: it indisputably needs fewer resources to produce the same amount (or more) of the desired outcome.
Indeed, the engineers will usually try to get to the bottom of what you mean by efficiency if you ask them for an efficient design. Especially if it's something that somebody's paying for.
They have quantitative definitions for some things like the thermodynamic efficiency of machines. On the other hand if you move into the domain of things such as enjoyment, they'll tell you to ask the marketing department.