built my own swingarm

[Nessism]

Wanna bet?

I would but not sure how we would settle it.

If the bet was who's closer but not over, you might win. But if the bet was who's closer, 25% or 4-6X, I'd win for sure.

[nastyjones]

Well, I guess I've had time to read all these threads and have come to ;the conclusion, there would be no harm in adding a brace to this swinger. I can have it welded for next to nothing
anyway so I am going to do that. I will also be extremely careful when I take my maiden voyage after it's finished. I realize I'm just a backyard engineer. By the way, I always wear my leathers and helmet.

Nastyjones

[chef1366]

Is this swingarm for dragracing?
This would be the questions to ask Einsteins

[nastyjones]

It's for an occasional blast down the strip but most of it's duty will be on the street. Why?

[skidMarkNZ]

pic,

nastyjones

How do i say this...

Screw it ill be honest...

You will die if you use that.

**shakes head and leaves thread**

[skidMarkNZ]

Well, I guess I've had time to read all these threads and have come to ;the conclusion, there would be no harm in adding a brace to this swinger. I can have it welded for next to nothing
anyway so I am going to do that. I will also be extremely careful when I take my maiden voyage after it's finished. I realize I'm just a backyard engineer. By the way, I always wear my leathers and helmet.

Nastyjones

Its your life dude, but when something breaks when you are doing 60mph and go into the path of an oncoming car or truck...

i don't think i need to elaborate.

[Hammered]

Dont be discouraged by the negative Nasty. Your design has a solid base. You just need to follow through. Most of the posters leaving negative replys have nothing more to add to your design because they cant. Continue to research some other swingarms and apply those ideas to yours. The main thing to remember is continue to do what you did with this thread, look for answers to questions you have.

[skidMarkNZ]

Dont be discouraged by the negative Nasty. Your design has a solid base. You just need to follow through. Most of the posters leaving negative replys have nothing more to add to your design because they cant. Continue to research some other swingarms and apply those ideas to yours. The main thing to remember is continue to do what you did with this thread, look for answers to questions you have.

Its not a negative reply, i'm not going to go hey good on you dude pat on the back for doing it yourself...

When i think it is a lethal mistake to be doing this...

Sugarcoat a turd all you like...

We arn't a "negative bunch" around here... good bunch of guys actually...

Just don't want to see somebody get hurt for the sake of saving some money by doing a DIY job...

it's posts of concern for his safety not of put down.

I just wanted to make that clear.

Mark.

[Nessism]

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

[Agemax]

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

be honest. would you trust that knowing that is keeping your ass from the tarmac?
ok its a start and maybe some more work it may look a bit safer

[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

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. .

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.