May The Fours Be With You

The inline-four cylinder is king, right? But what is it about this particular layout that grabs our imagination—especially when it seems so unsuited to everyday road use? Are we all power mad, delusional or is it simply that we like a challenge?

What’s made inline-fours the most successful of the multi-cylinder layouts. There’s no question that four-cylinder engines are the most popular choice for modern performance motorcycles, and cars too come to that, whether the cylinders are arranged inline, in a V or even in a square. But it hasn’t always been this way. It’s taken years of refinement and evolution for them to become what they are today— but what have four cylinders got going for them that other layouts in this series lack? Smoothness and mass-market appeal are two strong answers.

Regardless of any engine layout, designers are always sure to strive for two things: more power and more refinement than their competitors—something this layout lends its self too, even if it isn’t actually what’s best for the end users.

Top of the good list has to be the even number of pistons. This means inertial forces can simply be cancelled out by setting each pair of pistons to travel in opposite directions at any given time. Of course there are problems with secondary vibration but this affects nearly every type of layout, regardless of the number of pistons and can be dealt with effectively with balancer shafts and firing orders, or simply ignored. You also get a smooth delivery of power from the engine as it works as four smaller engines, rather than one huge thumper—which is great if you’re building a long-distance bike as it’s less fatiguing to ride.

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