Trike motorcycles are a unique but popular alternative vehicle. They run on 3 wheels hence the ‘tri’ part of the name. Trike motorcycles (or Trike’s for short) come in 2 formats mostly. 2 wheels at the back (known as the delta configuration) with 1 wheel at the front. Or 2 wheels at the front and one at the back, which is known as the Tadpole design.
The tadpole design are less common and harder to engineer. Due to the centrifugal forces when turning they don’t tend to be balanced well either, so it is normally professional companies which tackle that design. Delta style is much more popular for home built custom trikes.
A home built trike traditionally has a motorcycle front end (motorcycle forks, 1 wheel, 1 headlamp, fork suspension) and a custom rear end often modified from a small car chassis, to include 2 rear wheels, bench style seat and appropriate suspension.
A trike motorcycle does not have a roof (like a Reliant Robin) and is not a motorcycle with a sidecar. There is often confusion in defining 3 wheeled vehicles, but you usually recognize a trike when you see one as the are quite different to other 3 wheeled vehicles.
Trikes are not sold in mass numbers because they have a fair amount of negative points about them. Both compared to a car and a motorcycle. Motorcycles are out in the open, which feels nice, but leaves the rider vulnerable compared to a car where you are protected inside a large metal box. A trike is similar to a motorcycle in this respect. Because they do not lean to turn like a motorcycle they are usually a bit more stable though so often riders will not have a motorcycle helmet riding them. Cars have a disadvantage of being large and therefore can not squeeze through traffic jams like a motorcycle. Because of one half of a trike having a 2 wheeled base, they also sport this disadvantage.
As such Trikes will probably stay off the mainstream and kept being owned and made by eccentric enthusiasts who want something a bit different and to stand out from the crowd.