Dumb 'Girl' Question

[user 6393]

I have always been curious about the why's and wherefores of swingarms; single vs. dual.

Is there any particular reason why some bikes have one over the other? Technical advantages? or is it a weight or visual preference thing?

And yes, I do know what they are for.

Hey? It's not Friday...be gentle.

 

[Ignacio]

I think in theory the single-sided can be less weight than the conventional....and weight savings in "sprung" weight is always desirable on a performance motorcycle like a racer. Having less weight on the bits that move up and down makes it performa

And, of course, we like to have things that were on race tracks so it carries down to the consumer market.

Personally, I wonder about the forces exerted on single-sided swing arms and longevity....particularly those that are shaft driven units. It could be that BMW final drive issues are related to the fundamental design issues of the single-sided geometry. Ones with a chain are going to experience loads mostly along the long axis of the motorcycle while shaft driven are going to experience loads perpendicular.

...just a thought.

That and the single-sided do look cool.

 

[radman]

Beemer uses it solely due to it's making final drive replacement that much quicker, which has proven itself over and over and over and over.......................

 

[charismaticmegafauna]

Most of the motorcycle is "sprung" weight (held up by the springs) -- the wheels (and brake rotors, calipers, lower parts of the suspension, etc) are un-sprung weight. While it's true that less weight is, generally, desirable -- less un-sprung weight is especially desirable because it lessens the work the suspension bits need to do to control the movement of those pieces.

But..., a single-sided swinging arm may not (or, may?) be lighter. The choice may be made in a strength versus weight argument? Then, too, the benefit may be for rapid wheel/tire change ability (for a bike with racing aspirations)? Or..., just the 'cool' factor.

Some manufacturers have models that had single-sided swinging arms and have reverted to double-sided -- probably from the 'strength versus weight' argument?

One of the better designs I've seen has been the 800cc VFR arrangement for chain-drive. Now, if they'd just fully enclose the chain....

Ignacio's engineering query into BMW's rear drive failures issue seems interesting. I'm afraid, tho, it'll need someone with way more engineering expertise than me to illuminate....

 

[MotorToad]

The single-sided came out of racing. ELF developed it but I'm not sure what was the first bike to use it, surely an ELF endurance racer. I think the first bike you could buy with one was the RC-30. The sole advantage of it is easy rear tire changes. (Honda's SSSAs still mention ELF's patent on the arm.)

For an equivalent stiffness, the SSSA is considerably heavier. They're also dead sexy, so no one really cares about the weight.

 

[Ignacio]

Most of the motorcycle is "sprung" weight (held up by the springs) -- the wheels (and brake rotors, calipers, lower parts of the suspension, etc) are un-sprung weight. While it's true that less weight is, generally, desirable -- less un-sprung weight is especially desirable because it lessens the work the suspension bits need to do to control the movement of those pieces.

Thank you. I meant unsprung weight actually.....I flipped the two.

 

[Randy]

IIRC, in the mid/late 90s, Honda and/or Ducati race teams would switch back and forth between regular swingarms and single sided swingarms. At some tracks, they said the regular swingarm would work better and other tracks, the single sided swingarm was sufficient. At that level, you're talking about teams looking for tenths of a second over a 45 minute period. Don't think that level of finite tuning is required for street bikes.

I don't think that there is that much of a difference in the weight of the single sided swingarms vs conventional. The single sided unit may have less material, but, the material that is there is beefier. I do beleive, however, that the single sided units result in fewer parts which should be a plus for the manufacturers.

 

[Wolfhound]

Beemer uses it solely due to it's making final drive replacement that much quicker, which has proven itself over and over and over and over.......................

rad . . . :rofl: :rofl: :rofl:

 

[FastJoyRide]

Rear tire changes are also much quicker and easier than on say an ABS FJR!

 

[HaulinAshe]

I'm just trying to figure out why you tagged it a Dumb "Girl" Question?

IMO you asked a darn good question, regardless of gender. And kudos to the respondents today for quality, no BS answers.

It would be nice to see more of the same on this forum, so I'll stop trashing up this thread RIGHT NOW!

 

[eeksnake]

Along with quick tire changes, chain adjustment on the VFR's SSSA is so simple that even a brain-dead chimp like me can do it in less than 5 minutes. Just loosen the lock bolt, adjust tension with the spanner from the tool kit and torque the lock bolt down.

Easy-peasey!

 

[chrisflock]

For the race track, the single sided swingarm offers a big benefit for wheel changes, but what I've seen from looking back at various bikes specs (keep in mind, nothing scientific here, just randomly looking at bike models) it doesn't look like changing from a single sided swing arm to double-sided offers any appreciable weight savings, the single sided unit needs to be beefier.

Also, from an engineering standpoint, it is possible that using a single sided swing arm offers a design benefit...like say perhaps it allows them a bit more flexibility in the final drive of the transmission, especially on those bikes that have the swingarm pivot running through th rear of the engine/transmission case. It may allow the rear of the transmission to be asymmetric, with the final driven gear on one side, bearings in the middle, and the pivot point for the swingarm on and the front sprocket on the opposite side...

But for the street, it's basically for looks.

 

[airboss]

Along with quick tire changes, chain adjustment on the VFR's SSSA is so simple that even a brain-dead chimp like me can do it in less than 5 minutes. Just loosen the lock bolt, adjust tension with the spanner from the tool kit and torque the lock bolt down.
Easy-peasey!

+1, to all the above, you forgot it looks real cool.

 

[k7lvo]

Personally, I wonder about the forces exerted on single-sided swing arms and longevity....particularly those that are shaft driven units. It could be that BMW final drive issues are related to the fundamental design issues of the single-sided geometry. Ones with a chain are going to experience loads mostly along the long axis of the motorcycle while shaft driven are going to experience loads perpendicular.
...just a thought.

That and the single-sided do look cool.

Maybe BMW could start getting their single-sided swing arms and final drives from Honda....

 

[user 6393]

Thanks you guys for your patience with my question, and for your opinions and answers. Any day I learn something is a good day :yahoo:

I guess I'm just weird, but I am not fond of the single sided look. I don't see the 'cool' factor in it as I don't watch much racing (no access here in the boonies), and maybe the chicken in me wonders at it's safety as it just looks 'empty' on one side. I am sure the rear wheel could go flinging off at any moment with a dual set up too, but visually, singles make me nervous. That there is no real function, safety or performance difference, it is good to know it pretty much just comes down to preference. All good info to have.

Again, thanks!!

 

[Stephen]

Another reason: Single swingarms are popular with the "bling" folk. In addition to getting extended, it allows the rear wheel (chromed, etc.) to be seen, especially with a custom underbelly exhaust.

On a basic engineering level, the single sided swingarms give no significant increase in actual rolling performance.

 

[Auburn]

The bike in my avatar is a highly modified '89 Honda Hawk (650 cc Twin 37 rear wheel Hp in stock form) making 77 Hp at the rear wheel and came with single sided swing arms.

One of the reasons for a single sided may be to do with manufacturing process. The hawk swing arm was cast in aluminum in 2 pieces alnog the horizontal axis and then welded together which at the time may have been cheaper that welding up several pieces for a two arm swing arm. This was before a lot of robotic welding was done on the bike frames as it is now a days.

Another reason was for tuning the chassis. They could vary the swing arm wall thickness and internal webs to build rigidity in certain ares and flex in others. This would affect the overall handling and perfomance of the suspension as mentioned by others above.

 

[slapnpop]

You mean she wasn't asking about the Bimota? :lol: :huh:

That's where I instantly jumped, with dual swingarms. Only bike I know of with them, though I'm sure there's got to be more.

 

[user 6393]

I'm just trying to figure out why you tagged it a Dumb "Girl" Question?
IMO you asked a darn good question, regardless of gender. And kudos to the respondents today for quality, no BS answers.

It would be nice to see more of the same on this forum, so I'll stop trashing up this thread RIGHT NOW!

Mostly to avoid the possible dogpile. Thanks

And to the person who gave me sh&t in MSN? No, you don't have to come out here and kick my ass...