What Is It About Three-Cylinder Engines That Makes Them Music To Our Ears? | Cycle World
Courtesy of Triumph

What Is It About Three-Cylinder Engines That Makes Them Music To Our Ears?

Three points to consider: smoothness, starting, and natural evolution

I first heard the song of the triple in 1969, when Kawasaki made demo laps at Loudon, New Hampshire, with a prototype three-cylinder 500cc H1. Why does a triple make music, while a twin or a four, both of which share the triple’s even firing order, either drone (British twins) or shriek (Suzuki GSX-Rs)? There is the mystery. We love that triples sound.

Triples have never been more numerous. Triumph offers a family of triples. Yamaha has the FZ/MT-09. The reborn MV Agusta honors the many Grand Prix wins of Giacomo Agostini on his favorite machine, a triple whose life began in 1965 as a 350. Benelli offered a triple during its brief renaissance. And in the first years of the 1970s, triples were the leading edge of change: Triumph Trident, BSA Rocket Three, Suzuki GT750, and Kawasaki H2. A bit later, in 1974, came Laverda’s 1,000cc 3C.

Forget the questionable styling of the Tridents when they arrived in dealerships in 1969; hear their song at the Daytona 200 in 1970. And they would have finished that race 1-2 had the experienced Dick Mann not managed to keep his CB750-based factory Honda (the last one running) just out of reach of fast-closing Gene Romero.

In 1972, full 750cc two-strokes were written into AMA rules. What a symphony they made accelerating down Daytona’s pit lane! Suzuki’s 100-hp 750 was deep and throaty at its 7,600 rpm, while Yvon Duhamel on the 9,500-rpm Kawasaki H2-R set ears a-tingle.

Yamaha's popular FZ-09

Like Triumph's Speed Triple, Yamaha's popular FZ-09 (now known as the MT-09) is is powered by a three-cylinder engine.

Courtesy of Yamaha

Triples have always existed—at least since the single digits of the 20th century. DKW quickly stepped from single to twin to its famous 350cc racing triple of 1952. And then Saab at the end of 1955 released its 750cc Model 93 two-stroke automobile.

Consider propulsive smoothness: A four-stroke single in 1963 propelled me by a series of large thumps. A twin cuts the thumps in half and makes them twice as often. But a triple offers the beginnings of real smoothness, especially if it’s a two-stroke. Because in that case it becomes as smooth as the rightly admired four-stroke inline-sixes that BMW produces to this day.

Think about engine starting: As cylinders become smaller and more numerous, starting becomes easier because you are squeezing less mixture at each compression. On my single-cylinder AJS 500, starting became a circus act: Retard the magneto, “tickle” the carburetor, ease just through compression with the release then leap in the air to come down forcefully on what Vincent called “the commencer lever.” Electric starting was a relief to us all.

Another point: Triples happen almost naturally, and MV Agusta was a case in point. Count Agusta had seen it take years for the 350cc four (a heavy sleeved-down 500) to overcome Guzzi’s super-agile singles. The embarrassment! Therefore, the count let it be known to his race team that a cylinder should be added to the existing four-stroke 250cc twin as an experiment. After some inevitable trial and error, the result was an entirely new kind of 350cc racer—light and handy as well as powerful. A new synthesis. Let’s make a 500 of it!

That 500 was a sensational success in some of the most exciting races ever seen, as Agostini on the MV triple took not one but two 500cc championships from the elephant in the room—mighty Honda and its RC181 four ridden by the legendary Mike Hailwood.

Another fabulous triple came to be when Honda’s motocross engineer Shin’ichi Miyakoshi went to the Dutch TT and saw a replay of Count Agusta’s inspiration. The lap times of the light, responsive 250s were almost as quick as those of the heavier, tire-eating 500s. He thought, “What if we built a 100-hp 250 and entered it in the 500 class?”

When Honda’s preferred solution, the oval-pistoned V-4 NR500, proved too heavy and unreliable to win a single GP point, Miyakoshi’s thought experiment was officially ordered into hardware. Freddie Spencer won two races on the two-stroke NS500 in 1982 and the 500cc championship a year later. A triple was a well-balanced machine combining simplicity, light weight, easy handling, and competitive but not tire-killing power.

This reveals another fundamental truth of motorcycling, that it is a better idea to enlarge a smaller machine than it is to sleeve down a bigger, heavier one.

In terms of engine balance, a triple’s center of mass does not shake because, with its cylinders phased at 120 degrees, there is always just as much mass going north as south. But there is a rocking couple that causes the crankshaft to orbit as does a two-bladed kayak paddle in use. If the engine is quite heavy and/or low-revving (Triumph/BSA or Suzuki GT750) this rocking can be tolerable. But on Kawasaki’s lighter, higher-revving H2, the rocking couple set the bars into vibration, requiring weights to quiet it.

A case in point was Kenny Roberts’ water-cooled two-stroke KR3. Being very light (the FIM offered weight breaks for fewer than four cylinders) and initially designed without a balance shaft, its heavy rocking couple broke parts and messed up its carburetion. When retired Honda engineer Yoichi Oguma offered to redraw the engine with a balancer, things began to come together, and the bike’s star moment was Jeremy McWilliams’ pole position at the 2002 Australian GP.

Therefore modern triples are designed from the start with balance shafts that quell their natural rocking motion.

Killer horsepower attracts us more than compromise (Sylvester Stallone doesn’t appear in Negotiated Cease Fire III) but if we’re honest, most of us enjoy a well-balanced motorbike more than we do bikes with too much of everything. A triple might be “the Goldilocks solution”—just right. Think about it.