Swingarms explained

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Like sticky tape, motorcycle swingarms come in both single-sided and double-sided versions. Sticky tape may have come in handy for that Blue Peter project you attempted as a kid, but swingarms fulfil a much more critical function – they keep your rear wheel attached to your bike.

It may seem the kind of basic construction that could be accomplished by any GCSE metalwork class, but swingarms are much more high-tech than they look, whether they’re attached to the wheel on one side or two. They have to be, as the forces acting on your rear wheel are immense.

To get an idea of just how immense, drag out that old pushbike gathering dust at the back of your garage. Take one of the wheels off, hold it straight out in front of you and then get someone to give it a good spin.

You’ll find yourself fighting to keep it straight as the momentum of the spinning wheel exaggerates the smallest sideways movement, forcing it to slew from side to side. Now imagine how strong your swingarm must be to hold your bike’s rear wheel in check when cornering at 100mph.

Cornering forces aren’t all the swingarm has to cope with, either. It also has to withstand the twisting force from your final drive, whether it’s a chain or a shaft, resulting from the fact that it’s located on one side of the wheel only.

In addition, because the swingarm also forms a major part of the rear suspension set-up, it has to soak up the shock of bumps and potholes in the road surface, as well as support the weight of the bike and its rider, plus perhaps a passenger and a couple of hundred pounds of luggage. Also, when you accelerate from rest, the full weight of the bike acts on the back end, putting even more strain on the swingarm.

With all those forces putting stress on your swingarm, if you attached any old piece of metal to your wheel spindle you’d probably find yourself completing your journey on one wheel as the rear rolled away down the road.

Whether you have a single-sided or a double-sided swingarm, you don’t have to worry about that happening. Both types are designed to make sure they can withstand the considerable forces that are acting on them. But while there may not be any safety benefit to choosing one type over another, each one has advantages and disadvantages.

In terms of handling, you might think double-sided swingarms have the edge. After all, the vast majority of modern sports bikes use them, from Suzuki’s GSX-R1000 to Honda’s FireBlade to the R1 – in fact, Yamaha doesn’t have a single-sider in its entire range. But then you remember that one of the most iconic sports bikes in history, Ducati’s 996, has a single-sided swingarm and things get a bit more confusing.

In fact, it’s generally accepted that there’s little difference in terms of handling – at least none that you’d notice during day-to-day road riding.

But manufacturers have tried both designs almost since the dawn of motorcycling. Single-sided swingarms have been around since early in the century at least – the library of the Vintage Motorcycle Club records a James machine fitted with one being shown at the Stanley Show in 1908. The rear wheel was mounted on a stub axle on one side of the frame, with the belt drive on the other side.

Early modern single-sided arms were evolved by Honda for its RVF racers. Production Hondas followed in the form of the RVF750R and the VFR400R, but modern Honda superbikes have reverted to double-sided arms in line with its fellow Japanese manufacturers. However, there’s one very notable exception, in the form of arguably the best all-round motorcycle ever made, the VFR800.

Another early single-sided swingarm was used by BMW on the R80GS. Many other firms have produced bikes with the design, but none has committed to producing its whole range with the type.

The main advantage of the single-sided version is ease of maintenance. A single-sided swingarm makes it much easier to remove the rear wheel, provided the bike has a centrestand or you have a paddock stand to hand. This is a huge advantage in competition, especially in endurance events, but it also comes in very handy for the rest of us. If you have to replace your tyre, it’s much easier to whip off the wheel and take it to the fitter yourself, saving yourself a few quid.

Another advantage is cosmetic – the bike looks cleaner in design on one side. Some would argue that it also looks less symmetrical, but let’s face it, the 996 isn’t exactly ugly. It’s not just the design that looks clean, either. A single-sided arm has fewer nooks and crannies and inaccessible bits, so it’s easier to scrub chain oil off it. Less of the bike is hidden, so that grimy area around the rear wheel is less of a problem to get to.

The disadvantages are that single-sided swingarms have to be larger and more heavily engineered to enable them to cope with the stresses imposed upon them, increasing unsprung weight. Bearings also have to be larger and stronger to cope and an unusually large socket is needed to remove the wheel retaining nut.

Wheel alignment becomes a greater problem, too – it’s much easier to make adjustments to a wheel attached on both sides.

The overriding advantage of the double-sided swingarm is rigidity. It’s easy to produce strong, simple designs without complex production processes. Because the rear wheel is supported on both sides, wheel alignment and chain tensioning adjustment systems are easier to design. Weight distribution is better, too, in that there’s not a heavy arm on one side of the bike only.

The main disadvantage is the single-sided swingarm’s advantage – wheel removal is a much more laborious process and in an endurance event that could leave you languishing in the pits while your rivals are into the first corner.

For shorter events, both systems have their fans and both have enjoyed success. On the road, it largely comes down to personal preference.

It looks likely that double-sided swingarms will remain dominant in the future, but there will also always be a place for the single-sided version. Just don’t expect to see any made out of sticky-backed plastic and cereal packets.

MCN Staff

By MCN Staff