Large established manufactuers have a basic structural design that has been developed and refined over several decades.
Minor changes are made to this structure, which is primarily the chassis (e.g. BMW CLAR, VW MQB. Merecdes MFA).
Since production happens at very large scale in assembly-line factories, a single design is made for each usage class, and the design is done in-house, over several years, linked to a production process.
The design state-of-the-art is similar to automotive (e.g. Cradle, Diamond, Backbone frame types). The number of chassis designs is a lot larger and design revisions happen
twice as frequently as automotive.
Usage classes are based on engine size and weight.
There is more outsourcing of the design process, and smaller designers can exist, since a new design is a lot cheaper to protoype.
A bicycle is designed as a bicycle-frame only, by a an established brand (e.g. Diamond, Step-through, Cantilever frame types).
All other components that go into a finished bicycle are designed by specialised component manufacturers, such as
wheels and tires,
gear-shifting mechanisms,
brakes,
drivetrain components such as chain-cranks, chains and freewheels,
and shock-absorption systems.
Usage classes are based on terrain, targeted speed, loading level etc.
Of late, DC-motor based drivetrain assist sys
Motorised 3-wheelers are commonly produced industrially for cheap and traffic-efficient transportation (cargo and to a lesser extent passenger taxis).
This is a recent class of land-vehicles and only a few designs exist.
Tricycles, are very cheap to protoype. A handful of companies design and produce several such designs at very small scale.
In recent years, DC-motor powered cargo-trailers have also been designed
as bicycle add-ons, and have operational characteristics similar
to tricycles.
Low-cost commercial pushcarts are typically 4-wheeled with no steering control.