The Sound of Harley-Davidson

28th July 2022

Nothing else sounds quite like a Harley-Davidson.

For classic motorbike lovers – especially those enamoured with the legendary American manufacturer – the sound of Harley-Davidson bikes is all part of what makes these machines special. The sound is as much a part of the essence of Harley-Davidson as the bike’s look and feel.

 

What gives Harley-Davidson motorcycles their distinctive sound?

Potato, potato, potato! The distinctive sound of Harley-Davidson motorcycles is like music to an enthusiast’s ears. But what exactly makes the Harley-Davidson sound so unique? Let’s break it down.

A basic four-stroke engine works like so: a piston goes through the intake, compression, combustion and exhaust strokes every second revolution of the crankshaft – and the sound you hear is that of the compressed gases in the cylinder escaping, when the exhaust valve opens.

In a two-cylinder, horizontally-opposed engine, meanwhile, it’s a little different. The pistons are timed so that one fires on one revolution of the crankshaft – and the second on the next. To create this type of engine, the crankshaft has two separate pins for the connecting rods from the pistons. These pins are 180-degrees apart.

A Harley-Davidson engine, however, is a little different again: and that’s where the unmistakable sounds of a Harley come in. Harley engine crankshafts have just one pin, with both pistons connected to it. This design – along with the V-shaped arrangement of the cylinders – means the spark plugs fire at uneven intervals.

The resulting sound? A cadence Harley-Davidson describes as “pop, pop, pause” – or an engine rumble keen Harley enthusiasts have termed “potato, potato, potato”.

 

Did you know?

Engineers work in “total silence” rooms at Harley-Davidson’s product development lab. Why? To isolate where sounds originate, and minimise intake and mechanical noise so they don’t dilute the distinctive Harley-Davidson sound.

 

The Harley-Davidson sound lawsuit

They say imitation is the sincerest form of flattery: but when rival manufacturers tried to copy the sound of Harley-Davidson bikes, the legendary manufacturer decided to head to the courtroom. In 1994, Harley-Davidson filed for a federal trademark on their bikes’ “potato” sound.

Initially the U.S. Patent and Trademark Office granted Harley’s application, but rivals weren’t backing down: they argued that, because Harley claimed the sound was a by-product of its V-twin engine design, a trademark could prevent them using the same engine design.

The legal wrangling raged on for six years: but in June 2000, Harley-Davidson withdrew its application to patent the sound of its bikes, thus bringing an end to the lawsuit.