2 Wheels

The Honda RC166 Was a Race-Winning Miniaturization Miracle

For all their apparent simplicity, motorcycles can be just as varied as cars. Some bikes have 4 wheels, or even 3, for instance. But it’s in the engine department where bike designers can go truly crazy. Some bikes, like the Munch Mammut, use car engines. Others, like the Triumph Rocket 3, have engines so big they belong in cars. Then there’s the other end of the scale. Bikes like the Honda Super Cub, Grom, and Hunter Cub, which have tiny engines. But for truly going against ‘no replacement for displacement’, there’s no motorcycle quite like the Honda RC166.

Honda RC166 background

Although today Honda’s motorcycles have won Paris-Dakar races and coined the term ‘superbike’, in the early 60s the Japanese company was struggling. Remember, this is about a decade before Honda even considered selling cars in the US.

In the 1960s, Cycle World and 95 Customs explain, the motorcycle Grand Prix scene was mostly controlled by 2-strokes. 2-stroke engines, due to how they functioned, could develop large power from rather small displacements, Motorcyclist reports. 4-stroke engines were cleaner, quieter, and more fuel-efficient, which is why Honda founder Soichiro Honda devoted his company to them. However, other Japanese bike companies, especially Suzuki and Yamaha, invested heavily in 2-strokes, and so won many races.

Honda’s motorcycle engineers, though, were preparing something special. They made bike engines smaller, which let their pistons move faster. More revs mean more horsepower. That’s the solution modern bike engines use: small displacement, high redline. With this, Honda’s motorcycles were able to win the 125cc, 250cc, and 350cc World Championships in 1962. The 250cc and 350cc bikes won again in 1963.

1966 Honda RC166 side
1966 Honda RC166 side | Honda

However, by the following year, Honda needed to up its game once more. And in 1966, its efforts were capped by the Honda RC166. Because there’s another way to make more power: more cylinders.

What made the Honda RC166 special?

At the heart of the Honda RC166 is a 250cc six-cylinder engine, linked to a 7-speed transmission. That’s not a typo: 250cc, 6 cylinders. Its valves, Petrolicious describes, are the size of pencil erasers. The crankshaft’s components can allegedly be bent by hand, and some of its oil passages are less than 0.02” wide. And this was all designed and built by hand.

2020 Triumph Bonneville T100
2020 Triumph Bonneville T100 | Triumph

With 6 carburetors, this engine puts out 65 hp. Which doesn’t sound like much—but then, a modern Triumph Bonneville T100 only makes 55 hp. And it has a 900cc two-cylinder engine. It helps that the Honda RC166 revs to 18,000 RPM.

Not only that, but it redlines so quickly, riders could ruin the engine just by casually twisting the throttle. Still, the 65-hp engine was able to power the 282-lb Honda motorcycle to a top speed of 150 mph. Which, by the way, means it’s only 50 pounds heavier than a Grom.

And with Mike ‘The Bike’ Hailwood riding the Honda RC166, the company won 8 straight Grand Prix races in a row in 1966. Honda won the constructer’s title that year. And it won again in 1967, with Mike Hailwood once more riding the Honda RC166.

It still runs today

The Honda RC166 isn’t just a static museum piece. Honda still runs the bike on occasion for demonstration and celebration events. And in 2017, British road racer Steve Plater rode it on the Isle of Man Classic TT.

Modern road-going motorcycles don’t rev to 18,000 RPM. But it’s thanks to bikes like the Honda RC166 that the technology exists to let them rev even half as high. Over and over again.

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