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I have noticed that Ducatis , Honda and Triumph have bikes with a Single Sided SwingArm Much like most of the scooters.

Are there any advantages of following this design , if so why are not all manufacturers using it.

Why are all the scooters using a SSSA ?

I have not seen any scooter without a SSSA.

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The information provided by DucatiKiller is excellent.

I believe the biggest advantage is access, which makes wheel changes and maintenance arguably easier. This could also translate to pit-lane advantage in racing situations.

Particular case - in the case with Ninja H2R -

Having a single-sided swingarm allows the exhaust pipe to be mounted closer to the bike’s centerline, providing a high bank angle for sporty cornering.

Disclaimer - I actually have zilch experience about what I'm talking about-Fact.

While the point on SSSA being lighter sounds plausible, and it maybe true for certain case by case comparisons I'm not sure if that can be actually generalized.

  1. The SSSA would need to be structurally as strong as the double sided swing-arms and hence as such it wouldn't be lighter ?
  2. With SSSA you now have to engineer enough strength at the axle-pivot (?)(where the axle connects to the SSA) to counter the various moments of force, (it is in effect a cantilever kind of setup) which would have been balanced in a Double Sided Swingarm arrangement
  3. More material concentrated at the axle-pivot, add's to un-sprung weight, more so than the same amount of material evenly distributed over the swing-arm.
    All of the above is an over-generalized argument.

Why manufacturers go with a particular design in this case boils down to design decision which may even include aesthetics apart from engineering considerations.
Again, I'm not sure of any of the above.

  • well when i googled around , most of the answers reflect what you state.. so now again confused lol – Shobin P Jun 5 '15 at 20:29
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    yes, your dealing with another axis of stress with an SSSA. – DucatiKiller Jun 30 '15 at 8:48
  • @DucatiKiller I wonder why the 899 panigale doesn't have the SSSA. I confess I hadn't noticed it before this question :) – chilljeet Jun 30 '15 at 22:23
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    re. maintenance, it also eliminates the need to align the back wheel when adjusting the chain tension as there's only 1 adjustment point. – squigbobble Feb 9 '16 at 13:45
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Background

While various items such as maintenance and ease of tire removal are cited for the SSSA (Single Sided Swing Arm) design, initial testing and development of all these designs were started on the racetrack. Honda initially released their version of the SSSA with NSR250R.

image of an NSR250R

enter image description here

All of the early SSSA's were developed for racing to reduce un-sprung weight. From there, street sport bikes were the early adopters, porting the race technology to the consumer. This was followed by SSSA's on scooters and other non-sporting motorcycles.

While there is logic regarding reduced maintenance and ease of maintenance regarding SSSA's their initial adoption was for reduced weight and racing applications.

Un-sprung Weight

With all vehicles, un-sprung weight is the holy grail of handling. Un-sprung weight reductions result in a wheel getting back to the surface area it's adhering to in less time. The result is frequently less over-steer in cars and in motorcycles, less low sides due to interruptions in friction adhesion to the road surface.

Un-sprung weight or un-sprung mass is the weight that is not carried on the spring in your suspension. If it's below your spring it falls under this category. For bikes; the rims, tires, rotors, brakes, lower fork legs and swingarm all fall under the category of un-sprung mass.

The lighter this mass, the more responsive it can be to outside forces, responding as needed by absorbing energy, responding to undulations in the surface by not bouncing off the undulation and getting back to the surface of the road with it's full weight as quickly as possible.

To summarize the advantages:

  1. Less weight creates less momentum when responding to a bump or undulation in the road surface. More momentum in response to an undulation could result in the tire getting bounced off the surface of road.

  2. Less weight allows for the spring to push the unsprung weight back to the road surface quicker allowing for the contact patch to get back to work with friction for adhesion.

Why don't all manufacturers do it?

This is subjective, I believe it comes down to cost. If it were cheaper and there were performance advantages then I would imagine that everyone would engage in this design as a framework moving forward. It would seem there is a higher cost as only the higher end motorcycles like Triumph and Ducati are implementing.

The flip side is that due to lightweight materials and construction other manufacturers have found a weight/rigidity balance in there designs that allows them to be both competitive in the showroom as well as the racetrack.

Scooters

Again, this is subjective and opinion based.

Scooter swingarms are inclusive of additional properties other than rigidity for the rear wheel. Other properties of a standard scooter swingarms may include the following

  • Centrifugal clutch
  • Drive Belt tensioner
  • Shaft drive
  • Secondary shaft sprocket
  • Rear Brake

Here is an example diagram of Honda Ruckus that does not include the rear brake mechanisms within the unit. enter image description here

Due to the rigidity of the unit it only makes sense to make it all inclusive in a single sided swingarm. The unit provides multiple options for the various components as well as ease of maintenance for mechanics.

Additional benefits include ease of rear tire change for an end user that may not have the technical ability to line up a rear wheel properly with a traditional swingarm making for less service related mishaps and longevity of the vehicle.

Errata

Although car related, this kid has some excellent videos, a little long winded but very good information regarding suspension and the importance of a low unsprung mass in any vehicle. Have a look here.

Many manufacturers use a vacuum casting method to create thin walled high strength components. This a good video that illustrates the benefits.

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    Is there a maintenance/adjustment upside as well? Easier to swap rear tire for example? – Allman Jun 3 '15 at 7:39
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    Yes, it's one bolt for the triumph and ducati once the cover is removed. The eccentric adjusters all for a simpler chain tension process as well. – DucatiKiller Jun 3 '15 at 7:43
  • Great! From an engineering perspective, this is assuming that single sided swingarm is lighter. What are the factors that make this the case? – chilljeet Jun 3 '15 at 10:19
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    added a bit on scooters, subjective though. – DucatiKiller Jun 3 '15 at 19:12
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    Yeah, the kid is good. Like him. – DucatiKiller Jun 4 '15 at 6:20
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As a 35 year veteran motorcycle rider and owner of 15 different bikes during that time, while I don't dispute the unsprung weight argument made by DucatiKiller, I can tell you that there is a much, much, much more practical reason for using a single sided swing arm: It dramatically simplifies chain maintenance. You see, with a double sided swing arm, you must ensure proper rear wheel alignment with EVERY chain adjustment. The rear axel must be kept perpendicular to the swing arm. Getting chain slack adjusted is a fussy process, often requiring multiple cycles of loosening everything, making the adjustment to chain tension, and then tightening everything up again, measuring the new chain slack, and then (more often then not), repeating this. In addition, as the chain and sprockets wear out, the chain has loose and tight spots which can cause confusion with rear wheel alignment, as a tight spot on the newly adjusted chain can easily be a symptom of misalignment, (i.e., adjusting each side of the swinger's adjusters unevenly). And, if you misalign the rear axel you can cause the chain to become stressed and stretched, in addition to other problems. The single sided swing arm does away with all of that. The rear axel cannot become misaligned during routine chain maintenance, because it's alignment is permanently fixed relative to the single sided swing arm. Other maintenance benefits include easier rear wheel removal, tire pressure maintenance, and access to cleaning and inspecting everything in and around that area. Many manufacturers sell shaft drive motorcycles - not because shaft drive is more efficient than chain drive, (it is not), but because motorcycle owners are notoriously bad at keeping their chains adjusted properly, a problem that has always been made worse by the double sided swing arm.

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