SHAFT DRIVE vs CHAIN DRIVE

by Subroto Mukerji

My memory is not what it used to be. I confess I've gone and forgotten who invented the motorcycle! It was probably Gottlieb Daimler, the gentleman whose company later merged with Mercedes Benz to found the legendary Daimler-Benz AG.

No one, least of all Daimler, could possibly have foreseen, back then in the early 20th century, the shape of things to come. A hundred-odd years later, Daimler’s crude contraption has given way to humongous 21st century road-burners epitomized in 1800 cc of raw power that is the shaft-driven HONDA grand-touring wonderbike.

As the motorcycle evolved, controversy about the ideal drive mechanism hotted up. Which was the best way of transferring power from engine to wheels—chain…or shaft? There were as many supporters of either option as

there were manufacturers. Each option has its advantages as well as disadvantages.

Chain drive is light, inexpensive, rugged and shock absorbing. It stretches to soak up jerks from power surges due to throttle-happy wheelie-dealies and

also accommodates the swing caused by floating rear-suspension arms.

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On the downside is its tendency to over-stretch and become loose, eating up rear sprockets. Moreover, it can sometimes snap, which means untold misery as engines over-rev wildly and a bike suddenly becomes an unpowered, drifting, tractionless boneshaker that may prove hazardous in traffic situations.

Shaft drive has no such problems…modern versions even more so. There is direct transfer of power from engine to wheels unaccompanied by the excess baggage of lost throttle response. Efficiency is enhanced.

But a shaft is theoretically prone to even more wear

and tear than a chain, for two major reasons. First of all, a shaft isn’t flexible, and secondly, it cannot stretch to accommodate rear-arm (suspension) play.

Moreover, a shaft is, ipso facto, manufactured to miniscule tolerances that can be severely affected by the ingress of contaminants. Dust, the commonest example, can be a most effective abrasive especially considering the high rpms at which the shaft has to rotate.

To offset the disadvantages of shaft drive, highly advanced engineering solutions are called for. And these solutions were indeed found, as far back as the 1950’s.

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But sophisticated, close-tolerance manufacturing and the use of specialized steels, alloys, and rubber parts means extra expense and weight, and it is hardly remarkable that shaft drive was to be found only on the most expensive machines such as the superbly-crafted but exorbitantly priced British Sunbeam 500 cc of 1956, a bike I still salivate over.

BMW and the Italian Moto Guzzi (to quote but two of the most well-known examples) went the shaft route, and we all know how popular they are with the upper end of the market. However, where cost and economy were of paramount importance (as they undoubtedly were to the mass-produced low-end British and Japanese bikes), chain beat shaft every time. The amount of effort that has gone into making more durable motorcycle chains has paid off so handsomely that even a demanding but not-so-well-heeled buyer will not mind a chain-drive bike that otherwise meets all his expectations.

But give me shaft drive any day. Running silent, clean and cool in its sealed oil-bath, flexible couplings ensuring practically every bit as good resilience as a chain, and delivering torque as smoothly as a belt drive but with none of its unreliability, a shaft has as much lethal fascination as its Hollywood namesake John Shaft who, to quote the hype on the poster, is Hotter than Bond~ Cooler than Bullitt! 1

Subroto Mukerji

1 (Richard Roundtree as John Shaft in Shaft; Sean Connery and others as Bond; Steve McQueen as Detective Inspector Frank Bullitt in Bullitt)

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