built my own swingarm

[tkent02]

Welding a swingarm together is certainly no worse than what those bobber/chopper guys do to their bikes.

My first bicycle was a home made one, welded up carefully by hand. It was bought for me second hand, I have no idea who did the frame work. We were playing cops and robbers, blasting down the driveway when the steering head broke off. The resulting face plant was painful, and taught me a lesson.

Those chopper guys have obviously not been trained in this manner.

 

[posplayr]

Post for the morning

Post for the morning

Well I started with the first questions about stiffness of that swing arm.

When commented to nastyjones:

A note of caution: I hope you are in the process of bracing that arm. It looks extremely prone to flexing. :-k.

and he said:

I hadn't planned on bracing the arm. It is 1/4" steel and I just can't see flexing being a problem.

so I responded:

Go look at a modern sport bike and see what the swing arms look like. That should be enough to suggest to why any swing arm flex is bad and why people swap out for stiffer arms and brace arms than the ones you already have.

Given your comment about 1/4" steel, I'm assuming you have never taken a strength in materials class. Enclosed cross-sectional Area has more to do with stiffness than wall thickness. Actually it it is more precisely cross sectional moment of inertia, but I suspect that is not telling you anything.

Don't be surprised if your rear squirms around, in fact look out for it. This should be a learning experience for you; just wear a helmet and jacket.

When you do try and improve your arm, think about what makes an "I" beam stiff under bending moments but weak under torsional moments. It will help.

http://en.wikipedia.org/wiki/I-beam

You have since commented that you will relook at your design, which was one of my primary objectives. I commend you for pursuing this learning process.

Depending upon your inclination nasty, you might try and actually engineer a swing arm by attempting to size yours according to other designs, but you are going to need to have a basic understanding of the forces involved so that you know what you are looking at.

You have to understand that this is your project and none else is going to do it for you, but there is a concern by not just me that you will have definite safety issues putting what looks like a modified drag swing arm design on an early 80's street GS1100(all 550 lbs of it).

Ed posted a bunch of examples of extended drag swingarm, unfortunately those have nothing to do with turning. Agemax showed an awesome swingarm which should provide a clue that there are other forces involved when not turning that do not exist in straight line drag situations.

I hope you will continue your exploration, but keep an open mind to understand why other design that do exist are the way they are. There are mostly proven designs and so you can benefit from understanding why the work well. To help in this pursuit, I sketched up a crude drawing showing the differences in forces for straight line drag, v.s. turning forces.

The drag forces have no twisting effect, and only amount to a downward force that is offset from the rear axle by only a few inches. Basically the swingarm is simply there to space the rear wheel from the frame. Drag swingarms are spindly because there are essentially very low forces on them. In addition the impact of any vertical flex is almost in consequential as compression of the tire far exceeds anything that the swing arm will do.

On the other hand when you enter a turn, there are side forces on a tire which transmit to the frame. These forces are resisted by the swing arm alone. The twisting force tends to put the swing arm pivot axis out of alignment with the rear axle axis. Without going into a bunch of details, you can imagine that having a sprung hinge like this at the center of your bike is going to cause sudden changes in geometry right at the moment of peak forces in a turn. At the risk of over simplifying this, the above should provide a basic understanding the differences.

See the attached diagram as well.

Pos.

 

[Hammered]

Honestly Mark those are negative comments. Plus you provide zero input as to how to correct any defaults you believe the design has. And how could most of you who have no more experience in fabrication than he does, some may have even less. You can speculate all you wish but without some form of input as to how the design is flawed is personal opinion at best. And personal opinion isnt a bad thing but dont use it as the reason you know the design is flawed. And for those with a beef for chopper builders, you could learn a thing or two about innovation for them. Their not the sort to just change oil and such and say they build a bike. Or are satisfied with what was top of the line techology from 30 years ago. But thats ok, cause personal choose and the knowledge to create something many of you cant is whats make mine....well mine and not Mr. Suzuki's.

 

[skidMarkNZ]

Honestly Mark those are negative comments. Plus you provide zero input as to how to correct any defaults you believe the design has. And how could most of you who have no more experience in fabrication than he does, some may have even less. You can speculate all you wish but without some form of input as to how the design is flawed is personal opinion at best. And personal opinion isnt a bad thing but dont use it as the reason you know the design is flawed. And for those with a beef for chopper builders, you could learn a thing or two about innovation for them. Their not the sort to just change oil and such and say they build a bike. Or are satisfied with what was top of the line techology from 30 years ago. But thats ok, cause personal choose and the knowledge to create something many of you cant is whats make mine....well mine and not Mr. Suzuki's.

ahh my input into fixing the design is put something off another bike in as opposed to something build in the back shed...

whatever eh, you back him up so much anybody would think you ride honda's

 

[80GS1000]

Nasty-

If it were me, I'd find an existing production swingarm and copy its bracing. That way you're emulating a tried and tested product designed by people with pocket protectors.

Bracing along the lines of the ZRX1200 swingarm would sort you nicely by minimizing the side-to-side flex in your original design.

Or just buy a GSXR swingarm and swingarm extensions off eBay, weld on some shock mounts, and call it a day.

 

[Agemax]

Nasty-

If it were me, I'd find an existing production swingarm and copy its bracing. That way you're emulating a tried and tested product designed by people with pocket protectors.

Bracing along the lines of the ZRX1200 swingarm would sort you nicely by minimizing the side-to-side flex in your original design.

Or just buy a GSXR swingarm and swingarm extensions off eBay, weld on some shock mounts, and call it a day.

that sounds like a much safer idea to me. my swingarm was built to order but a standard gsxr swing arm will fit with minimal mods.as mentioned just add shock mounts and your done.
paint or polish or chrome then, the world is your oyster but you know you will be safe

 

[Nessism]

I think that swingarm will be perfectly serviceable after some bracing is added in front. No need to go to engineering school before you mod your bike. The size of those legs are significantly larger than the stock arms, so it will be plenty stiff, again, after the front is tended to.

While investigating that front bracing, make sure your axle securing method is robust. It's a little hard to tell from one photo. Also, make sure you get the side to side spacing correct and use solid spacers to center the wheel.

You are off to a fine start, now finish the job.

 

[Nessism]

that sounds like a much safer idea to me. my swingarm was built to order but a standard gsxr swing arm will fit with minimal mods.as mentioned just add shock mounts and your done.
paint or polish or chrome then, the world is your oyster but you know you will be safe

Is a GSXR swingarm 4" longer than a stock GS1100 swingarm?

 

[Agemax]

Is a GSXR swingarm 4" longer than a stock GS1100 swingarm?

it is when you buy a one off swing arm with extra bracing and 6" wheel travel.
as mentioned before, you can buy the extensions quite easily from various places

 

[80GS1000]

Is a GSXR swingarm 4" longer than a stock GS1100 swingarm?

That's what they make GSXR swingarm extensions for.

 

[errorcauser]

If it were me, i'd add a solid steel piece up next to the front, somewhat like the shape of this.. (i made this don't laugh)

Wouldn't have to be exactly that shape, but a good solid piece of steel welded in there correctly and that thing should be like a sherman tank, no ?

 

[Nessism]

That's what they make GSXR swingarm extensions for.

Looks like they would make for a nice swingarm. Not exactly for those on a strict budget though.

 

[Hammered]

whatever eh, you back him up so much anybody would think you ride honda's

Im gonna have to assume that the riding of a Honda is an insult?!?! ;/shurgs:

Im backing this project because it show initiative. Believe it or not, a fully functioning, safety minded, balls to the walls swingarm can be made with a few tool anyone of the members of this board could purchase and use with skill. Some skills in fabrication and welding will need to be learned or shopped out. And this is what I like about Nasty's project. He's stepped out of the "lets just buy something and bolt it on" mentality. I still believe some thought into the bracing needs to be addressed, but hes posted, thats exactly whats hes doing. I think this project has a great start and merits creative and informative input and not,

How do i say this...

Screw it ill be honest...

You will die if you use that.

**shakes head and leaves thread**

 

[Agemax]

Looks like they would make for a nice swingarm. Not exactly for those on a strict budget though.

couple of hundred bucks for a second hand swingarm , a pair of extensions and a bit of welding........or 6 months off work and a trashed bike?

 

[Hammered]

If it were me, i'd add a solid steel piece up next to the front, somewhat like the shape of this.. (i made this don't laugh)

Wouldn't have to be exactly that shape, but a good solid piece of steel welded in there correctly and that thing should be like a sherman tank, no ?

Thats a great gusset design. The reason I like this is, it not only will stiffen against the twist created by the torgue but will also allow for the expanding size of the tire at high RPMs of tire. If youre worried about weight from a plate, you could have this cut as 2 piece (top and bottom) from something thinner and have it bead rolled to stiffen the piece. Like the fllorboard in the picture below. You can go with a thinner gauge shhet steel and add the it rigidness but having it beaded.

I would pick a higher grade, cold rolled sheet steel to have these made from.

 

[Nessism]

couple of hundred bucks for a second hand swingarm , a pair of extensions and a bit of welding........or 6 months off work and a trashed bike?

Silly post. Building your own swingarm does not automatically cause "6 months off work and a trashed bike". How do you come up with this stuff?

And purchasing a used GSXR swingarm, buying the extensions, having someone weld them for you (welding aluminum is not as simple as welding steel), coming up with the shock eyelet, having all the parts freighted in, etc is going to cost several hundred dollars. Not everyone has this kind of money laying around to blow when a simple rectangular section steel swingarm will get the job done for only a fraction of the cost.

 

[Agemax]

Silly post. Building your own swingarm does not automatically cause "6 months off work and a trashed bike". How do you come up with this stuff?

And purchasing a used GSXR swingarm, buying the extensions, having someone weld them for you (welding aluminum is not as simple as welding steel), coming up with the shock eyelet, having all the parts freighted in, etc is going to cost several hundred dollars. Not everyone has this kind of money laying around to blow when a simple rectangular section steel swingarm will get the job done for only a fraction of the cost.

you missing my point mr nessism. building your own swing arm is fine if you know exactly what metal you are using, grade, strength, thickness etc. then getting your angles and dimensions right.
bearing housings and rear wheel alignment is critical, as you have mentioned in other posts.

lashing together a swing arm in your shed with substandard metal and non proffessional welding (judging by the pics) will ultimately lead to a catastrophic failure, especially if the guy plans on doing a few drag passes.that will lead to 6 months off work and a trashed bike!

would you make your own crash helmet just because you think you are a wizard with fibreglass?

DONT THINK SO

 

[KiwiGS]

Firstly Nasty good on ya for having a go mate.
I have thought about making my own swingarm, but when I spoke to my bro (who is an engineer and very qualified welder) I decided against it.
for one big reason COST even with out the labour the materials were going to cost more than a factory swinger.
I was aiming for lightness and rigidity and that doesnt come cheap.

Some one said you need a gusset, I would agree with that 100%.

Once some sort of gusseting is included in the design *I* cant see Nastys swingarm being any worse than the one that was on my GS1000, just a bit heavier.

Cheers

 

[Hammered]

Agemax, Im a certified welder. Have been for over 25 years. Ive been certified in most phases of welding. My work has been tested to 6000psi on pressure vessel and Im currently carring a 6G structual cert. And have all my background in welding and fabrication, I cant tell from the photos whether those welds are structual. Pretty doesnt make strong. For all you know, these joints ARE slugged and were welded using an Oxy/Ace torch and will out last any connection on your bike. My point is, you dont know. Now if you have some input as to how to better the design, Im sure Nasty would welcome it.

 

[Agemax]

Agemax, Im a certified welder. Have been for over 25 years. Ive been certified in most phases of welding. My work has been tested to 6000psi on pressure vessel and Im currently carring a 6G structual cert. And have all my background in welding and fabrication, I cant tell from the photos whether those welds are structual. Pretty doesnt make strong. For all you know, these joints ARE slugged and were welded using an Oxy/Ace torch and will out last any connection on your bike. My point is, you dont know. Now if you have some input as to how to better the design, Im sure Nasty would welcome it.

my input is my own safety, full stop. another thread where people may label me as selfish, but i dont care. i would not trust that swing arm on my bike,end of story.
and how do you know who welded my bike and what with? you would be very surprised!!!!!