[Spitfired]

So here's my bike dubbed the Connectfour, for 4x racing and general trail/freeriding.
130mm Travel
69 head angle (w/ 130mm fork)
This setup with 38lbs, but my wheels are setup pretty heavy (bought them for downhill use)
I currently have some swingarm flex issues which I am in "maximum engineering mode" trying to take care of. Braces, stiffener links, and possibly more tubing in the next few weeks. So, if any of you builders have any suggestions for stiffening the rear end, I'm all ears. I tihnk the rectangular tubing is the main flex point as it's not really withstanding the torsional flex.
At last, here she be:

 

[TheInedibleHulk]

I like the pierced top tube and the geo sounds good, but I can definately see why the back end is having issues... it looks flexy

I dont build bikes but I do some structural metal work for car stuff. Those chainstays seem awful tiny and you're probably right about the square tubing. I cant quite tell, are your seatstays made out of square tubing as well? You want the vast majority of the torsional load on the chainstays, since they meet the uprights closer to the pivot. It looks like right now your seatstays are bigger than your chainstays, which with a design like that is bad juju. Since the majority of the tonsional load is on the seatstays, you have to fight twisting for the whole length of the uprights. By uprights I mean the short side of your rear triangle, for lack of a better term to call it. I would make the chainstays much bigger, and then reinforce the uprights from pivot to chainstay junction with some kind of gusset.


All that said, I think your bike looks awesome and to workmanship looks great. I would maybe brace up the current back end a bit to ride it and start working on a redesigned one.

 

[binary visions]

Looks great - did you weld it all yourself as well?

Must be a blast to ride something that you got to design yourself!

 

[whoopnar]

Nice workmanship. The rear end looks like an old Santa Cruz Heckler or Superlight, and I am pretty sure they were pretty flexy as well.

 

[eastcoastzigzag]

looks mean!

 

[peyto]

So, if any of you builders have any suggestions for stiffening the rear end, I'm all ears. I tihnk the rectangular tubing is the main flex point as it's not really withstanding the torsional flex.
QUOTE]

Nice work. I'm actually working on something fairly similar to that right now. To stiffen things up I would increase the size of the rectangular uprights and maybe use an asymetrical swing arm.... No need for the left side "chainstay" to be elevated.... Do you have a brace between the uprights other than at the shock mount? That would help.

EDIT: you might also want to look at your main pivot. It looks a little undersize. Can't really see though.

 

[speedster]

The rear end is flexy because 1.) small, long and pobably thin tubes 2.) there is no cross bracing. I would recommend a one piece brace that connects both the chain and seat stays and put it as close to rear wheel as possible watching clearance issues, mud and tire. Watch the size of the brace though as you don't want it to come in contact with the frame at full travel. Another option would be to add a few gussets on the rear, but that is just another idea, I am not sure how much that would help as most of the bending and torsion is happening in the middle of the tubes. Hope this helps

 

[Westy]

It is hard to tell if it is already done or not from the pictures. But if you think that the majority of the flex is coming from the rectangular tubes, just box them in. That should stiffen things up and not require a new rear end to be built.

 

[Superdeft]

Unless the aesthetic look is a top priority, you might want to consider moving the non-drive chainstay down near the pivot for more stiffness.

 

[CBJ]

Nice looking bike - keep us updated on the progress of the frame.

 

[zedro]

getting a plate just at the tire linking all 4 members will do wonders

 

[Spitfired]

Between stays any braces have to be bolt on, otherwise you won't be able to get the swingarm off.
One of the things I have planned for friday (15 hours of milling, woo!!) will be to make those bolt on braces.

I was thinking about running a tube from pivot to mid seat stay on the non-drive.

Pivot is 15mm; I'm considering getting 17mm bearings with the same OD and width and opening up the front triangle a little.

Thanks for the positive response, I love to hear it!

 

[Orvan]

sweet looking.

 

[zedro]

Between stays any braces have to be bolt on, otherwise you won't be able to get the swingarm off.
One of the things I have planned for friday (15 hours of milling, woo!!) will be to make those bolt on braces.

I was thinking about running a tube from pivot to mid seat stay on the non-drive.

Pivot is 15mm; I'm considering getting 17mm bearings with the same OD and width and opening up the front triangle a little.

Thanks for the positive response, I love to hear it!

oops, totally forgot about that. Guess you could weld tabs onto the stays and have a mid-plate bolt to all 4 corners; that way it'll stay low-profile if space is a concern.

man, i really want to build another bike again....

 

[Acadian]

wow that is pretty nice...I like that Nice and simple, yet custom - all you need for 4x and DS.

I'm no engineer so I'm not the one to give suggestions as to how to re-enforce the swingarm, but I'm sure you'll get plenty of suggestions from others.

Raw look is killer.

 

[peter6061]

I think the bike looks sweet!

I know you mentioned adding braces, tubing, etc,... but is there anything joining one side of the rear end to the other besides the pivot, shock and wheel. You would get a ton of flex if those pieces were independent. A nice tube or two connecting the pieces together on the square uprights should do the trick. Also maybe a bolt on brace back on the seat stays above the tire.

The design itself looks nice and reminds me of a SC Superlight, but strengthened and setup for 4X.

Nice to see people actually doing as opposed to just talking.

 

[Spitfired]

Yes, between the rectangular uprights there is a section of .75x1.5 rectangular tubing.

I did a great job overlooking the swingarm and I can't thank you guys enough for your ideas - I was on the verge of just scrapping the design (mostly out of immediate frustration I suppose) but I think I know what must be done now.
Rock on.

 

[UiUiUiUi]

Yes, between the rectangular uprights there is a section of .75x1.5 rectangular tubing.

I did a great job overlooking the swingarm and I can't thank you guys enough for your ideas - I was on the verge of just scrapping the design (mostly out of immediate frustration I suppose) but I think I know what must be done now.
Rock on.

damn you scrap the design and err... give me the "trash" for free

sweet looking bike!!!

 

[dexterq20]

Does it come in rootbeer?

 

[allsk8sno]

sweet!! now just make it so you can add a longer shock for say 6 or so inches
and shorten the tt and my wife will love it as a dh bike!!!(she is 5'2")

i want to make a bike so bad...

 

[Kornphlake]

I can't tell what you've got holding your rear wheel on but it looks like you might be using a QR, a bolt on axle should add some stiffness to the rear end.

 

[dhtahoe]

Zedro is on the right track, and then you hit it right on the head. That's what SC does on the Superlight. Bolt the brace on. It's steel not like you have to re-heattreat after you weld.

 

[HRDTLBRO]

Damn!
Nice fab! The headtube junction looks great, as does the dropout system...care to take closer shots? With the simple, clean lines, it looks very astheticaly pleasing! I've been designing something very similar, i'm tired of these long travel trail bikes. I've been wanting a burly, tight, and stiff short travel bike to jump and race. My current draft uses a rear similar to an orange, but I may use regular tubing since it's a bit easier to fabricate. I'd agree in making some bolt-on braces. You can play with different brace designs nd construction to find the optimal strength. Clearcoated raw= :evil:

 

[draco]

see G? totally fixable.

I mentioned the bracing, the asymetrical Ndrive chainstay, etc. I think its fixable no doubt, but my feelings on .5x1" uprights and .75"diameter tubing for the stays... stays the same... lil small.

having ridden the bike.. the geo is pretty damn nice.
( i welded it! woop woop!)

^^^^^^
shameless self promotion in the name of helping a homie get his bike running.

 

[TheInedibleHulk]

Do you own your own tig welder or did you weld this somewhere else?

 

[DHS]

Do you own your own tig welder or did you weld this somewhere else?

i believe Draco john did the welding. they have their own setup. wish they would take me out there so i could see the new place.
i hate you guys, boo hoo.

 

[Dylan]

got a kick outta the name "connectfour" haha cool looking bike!

 

[Spitfired]

Does it come in rootbeer?

No, I'm sorry.

It comes in cream soda though!

 

[dropmachine]

Having a main Pivot the size of a pigeons arsehole definately doens't help. It seems that a lot of companies just don't understand that concept though, so don't feel bad.


Looks awesome though, great work! Wish I could do something like that.

 

[Bikael Molton]

What are you using for materials?
Won't you need butted, high-end steel in order to get the weight down enough for 4x?

Keep it up! (Steel addict here.)

-rob in Brooklyn

 

[COmtbiker12]

Wow, that's definitely a sweet bike!! Looks beautiful. i wish I had the skills/knowledge to design a bike like that on my own.

 

[Spitfired]

Having a main Pivot the size of a pigeons arsehole definately doens't help. It seems that a lot of companies just don't understand that concept though, so don't feel bad.

Whoa. That's one loose pigeon. 15mm loose, to be exact.

Yeah, like I said earlier (maybe?) I have a tendancy to underdesign then be like "what the fark was I thinking?"
15mm main pivot is retarted for a single pivot. Seriously retarted.

Rob in Brooklyn - It's straight gauge 4130l. Once I get the design perfected, I just might go for some butted tubes for the "team race limited special edition" or whatever. The frame is pretty light. There is at least 4 pounds to be shaved through the wheels and maybe the cranks/bb.
A set of Shimano Hone and some crossmax wheels would hopefullly bring the bike in around 30~32lbs range. Fork's kind of heavy too. A minute would shave another 2lbs off.
That would be sweet!!

Once again, loving the response.
I'll be keeping you all updated as to what goes on it this week and take some pictures that arn't so blurry.

 

[-BB-]

How about a 12mm rear axle?

 

[bballboy388]

it looks like they just f***ed up on a hardtail donno why everone is so pressed on it im fine with my ****ty bike.

 

[zedro]

Whoa. That's one loose pigeon. 15mm loose, to be exact.

Yeah, like I said earlier (maybe?) I have a tendancy to underdesign then be like "what the fark was I thinking?"
15mm main pivot is retarted for a single pivot. Seriously retarted.

i think alot of single pivots even come in at 12mm or 10mm, so 15mm isnt that small in the field. What will affect the stiffness mostly is the width and outside diameter of the bearing since they're mounted to the swingarm (on a frame mounted bearing setup, the ID would bear on the stiffness). The design and interface between the bearing and the swingarm can make or break you.

I tend to overbuild, using 52x25x15t main bearings with 47x30 thrust needle bearing on my bike. Now thats overkill, but it looks awsome

EDIT:

Pivot is 15mm; I'm considering getting 17mm bearings with the same OD and width and opening up the front triangle a little.

i wouldn't do it because you'll decrease the width of the bearing. The 15mm ID is plenty stiff assuming you dont have alot of clearance between the bearing and frame.

 

[buildyourown]

Drop the non-drive side chainstay. Chop the old one out and weld in a new one. Then make a brace for it. That will be a tricky brace to make. If you are doing this manually, you should have some fun. Those of us with Mastercam and 5 axis mill get spoiled.

 

[Spitfired]

Brinkman CNC laboratory, DUH!

 

[Tame Ape]

Put in a swing link a la foes. That something I would have loved on my Heckler...

 

[Sir Happypants]

maybe a stiffener link on the top tube... definetly one of the coolest threads in a while

 

[Jm_]

The biggest problem overall is the design, it's why yeti, foes, ventana and others add a "swing link" to their similer bikes. That swing link does a lot, because no matter how big you make the tubes, how big the pivot is, how much "reinforcement" you add to it, nothing makes as big a difference as having that swing link in there to stiffen the rear. Otherwise the "rear triangle" is sitting on that "post" that connects with the main pivot. The "post" is fairly easily twisted by lateral forces, forcing the shock to act as a frame member and putting tons of stress on it that it was not designed to take.

It's not that you can't make it good by doing all of the things suggested in this thread, but the biggest improvement would be to do somet of those, but design in a swing link, and then you'd get lots of lateral rigidity. The heckler/superlight/bullit/haro single pivot design does not lend itself to lateral rigidity.