Why Inline Fours?

Why do the major manufacturers race, market and sell inline fours?

I can only think of:

1. It's The Rules (but AMA has provisions for different engine formats)

2. It's the Horspower (yet in MotoGP [fastest series] most bikes are
not inline fours)

3. It's the Consumer (can't argue this either way but L-twins, V4s and
Triples sell)

4. It's Cheapest (doesn't seem logical)

So, why is it?

EZ

 

A tradition that begun in the air-cooled era.
The only way to properly cool 4 cyls with riding wind is having them
inline, across the bike.

Also, a crank shaft that is perpendicular to the length of the bike
has major benefits: bike remains upright when revving up or down
(unlike a 2cyl bmw), and it is easy to hook up drive axle with rear
wheel via a chain.

Bram

 

It's a combination of several factors, including cost and performance.
In production based racing (WSBK and AMA), the bikes must retain
production engine architecture at the minimum. So if you're selling an
inline-four, that's what it must be in race trim. In terms of
production, making 1 head per engine instead of 2 is a huge cost
savings. Ever wonder why twins get to be more expensive? You're
paying for an extra crank, extra cam chain, extra cam chain tensioner,
etc. A single head engine also allows for a much easier time shoving
it as far forward as possible making for a nice long swingarm, which is
a performance benefit.

In terms of cylinder count, 4 is a pretty good number as far as primary
balance in an inline arrangement. I don't recall how well balanced a
90 degree V-4 is, but I suspect it's not too bad.

When it comes to pure bred racing machines you see in GP's, the engine
architecture is dictated by mass centralization, other component
arrangement, performance-driven cylinder count (4's and 5's get to have
the same min mass, so 5 is better than 4), and power delivery. That
last one is where we see engineers' ideas in the most obvious sense.

Consider V-4 vs I-4. The only thing that really changes from one to
the other is where the power pulses happen in relation to one another.
In an I-4, a street firing order is: 1, 2, 4, 3. Each pulse is
separated by 180 degrees of crankshaft rotation. You can switch that
to a big bang style firing order with something like this: 1 & 4, 2 &
3, nothing, nothing. So you get one big pulse, 180 degree rotation,
another pulse, then 450 degrees before the next cycle.

I've never had a V-4, so I can't pull up firing orders off the top of
my head, but the moral of the story is that in a V configuration, some
of the firing pulses mentioned above can be offset by the angle of the
V. In a sense, a road going V-4 is closer to a big bang configuration
right out of the box because it's not gonna have evenly spaced pulses.
So some people consider it a good compromise between a big bang I-4 and
a screamer I-4.

But now the world's changing rapidly because electronics are getting
better and better. The computer, traction control in particular, is
taking over more and more of the power delivery problems and solving
them for the rider no matter what the firing order is. And, while
still important, I suspect reliability (primary and secondary balance)
is gonna be more a factor then with the 800's than power delivery on
its own.