三轮车 - why have four wheels when three will do?

In the United States, the realm of three-wheeled vehicles is reserved
for toddlers. Americans simply don't hold much stock in odd numbers of
wheels. My deep inspection of our culture (read: the thoughts that
popped into my head when I think of 3-wheels) has even discovered a
possible dislike and inferiority associated with vehicles that do not
possess only pairs of wheels. Phrases such as "third wheel" indicate
awkward and undesirable situations. This is not the case in China.

Vehicles of 3-wheels are perfectly acceptable and commonplace. Almost
any normal vehicle will also come in a 3-wheeled variety. I first
found it comical � afterall, I am subject to my cultural roots of
3-wheel ridicule. There are all sorts of tricycles ridden here, along
with many small cars of 3-wheels. Tri-wheeled cars appear to seat from
a mere two passengers up to a potential of five. My father and I once
spied a minivan possessing only three wheels � perhaps bringing a
whole new form of mini to the van. Most vehicles of three wheels are
good, common working machines. Extremely common are the 三轮车
(san1lun2che1 � literally "three wheel car") pictured above. It seems
to be the modern adaptation of the sedan chair or any other
human-powered mode of transportation. Everything about them eluded an
air of casual everyday life, from the variety of the operators -
grizzled old men, young men, a portly middle-aged woman or two � to
the variety of passengers � guys in business suits, young couples, the
ever-present grandparent and grandchild pair.

The tendency towards three wheels instead of four speaks to me of
China's ruthless efficiency. If three will work, why bother with the
fourth? Not only do you save on the initial cost, but on the
efficiency of having to move less mass for the entire lifespan of the
vehicle. Three-wheelism is therefore a perfectly reasonable
conclusion. Of course, this decision for efficiency is not
stigma-free. Those who can afford the fourth wheel will often indulge
in it, perhaps not simply for the additional stability but to show
their position beyond 3 wheels. Most 3-wheeled vehicles are those of
the hard-labor classes. Trucks transporting fruits and vegetables from
the local agricultural areas around the city are always of only three
wheels; motorcycles of three wheels are such that the last two wheels
support a large platform that can be used to transport everything from
workmen to marketwares. For these purposes, it appears as though
leaving off the fourth wheel is merely a matter of efficiency and
optimization.