Chain, belt, drive shaft. Each setup has it’s own pros and cons, but which system is best? In this video from the MC Garage we’ll discuss the three forms of final drive so you can decide for yourself.
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Drivetrains don’t get a lot of credit. The engine—which makes the power that hurtles you down the road and produces that sound and feel that bring a smile to your face—gets all the glory. But if that torque weren’t transmitted from the engine’s output shaft to the rear wheel you wouldn’t be going anywhere. And for that reason, this MC Garage is dedicated to the final drive in its three forms: chain, belt, and shaft.
Are Motorcycle Belt Final Drives The Best?
Chains are far and away the most common form of final drive today, and while the idea of a roller chain can be traced back to the sketchbooks of one Leonardo da Vinci, the first motorcycles weren’t chain-driven but belt-driven.
Belts were originally cut from the most durable material available: cowhide. Leather belts tended to slip, wear, glaze, and break, so they were quickly phased out in the first part of the 20th century in favor of chains and drive shafts. Look around any dealership though and you’ll see that belts are back. Belt materials and manufacturing technology made big enough strides that by the 1980s belts were tough enough to be used on bikes again. Belts are mostly used on cruisers, but BMW and electric motorcycle manufacturer Zero have employed belts on sportbikes because they offer some distinct advantages over the ubiquitous chain drive. For starters, belts don’t need lubrication so they’re cleaner. Belts are also quieter, offer a long service life, and—besides the occasional visual inspection—require very little maintenance.
If belts are so great, why don’t we see them on other types of bikes? Packaging and difficulty of replacement are the biggest drawbacks. Today’s synchronous (toothed) belts are as strong as chains and not much wider, but they can’t wrap as tightly so they need a larger countershaft pulley (and correspondingly large rear pulley to attain the proper gear ratio) than a chain setup. And when it comes to replacing a drive belt, the process usually entails removing the swingarm.
So That Means Shaft Driven Bikes Are The Best?
Driveshafts must be the best form of final drive, right? Those who have them on their bikes certainly think so, and shafts have been the final drive of choice for BMW since 1923. “The historical use of shaft drive is primarily for longevity and minimal maintenance requirements,” Communications Manager at BMW of North America Roy Oliemuller says. Driveshafts are nearly maintenance-free, impervious to the outside environment, and—barring any sort of freak failure—will last the life of the bike. All strong benefits, but shafts are also costly to build, heavy, and sap more power than other final-drive systems. And unless the manufacturer wants to build and fit two sets of expensive, power-robbing bevel gears, drive shafts are best reserved for engines with longitudinal crankshafts. Shaft-jack under load used to be an issue as well, but clever linkage arrangements have almost eliminated it.
Ok, What Makes Chains The Best?
That brings us to the roller chain, the most prevalent form of the final drive. As with most things that are mass-produced, the cost is a huge factor, and chains and sprockets are cheap to make. They’re also compact, fairly durable, easy to replace, offer easy gearing changes, and are the most efficient means of power transmission. Yes, chains require regular cleaning and lubrication, tend to make a mess of things, and wear out much faster than belts or shafts, but every form of final drive is a compromise.
Chains are in essence just a series of plain bearings linked together via inner and outer plates. Unsealed chains were the norm for decades, but they were difficult to keep lubricated so wore quickly and necessitated regular adjustment and replacement. Then someone came up with the clever idea of permanently lubricating the parts of the chain that need it most—the pins and the bushings that rotate on them—and the sealed chain was born. In sealed chains grease is drawn into the bushing by means of vacuum when the chain is assembled, and then rubber O-rings squeezed between the inner and outer link plates seal in the grease and seal out dirt and water. Sealed chains offer considerably longer service life compared to their unsealed counterparts.
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