Custom frame tube size

[Chuechco]

Hi,

I'm working on a bike frame and have a question regarding the size of the rectangular tubings.
That's my frame:

Each color stands for a specific tube dimension.

red : 30x15x2 used in the main frame
red-orange: 40x20x2 used in the swingarm
orange : 20x20x2 used in upper arm of swingarm
violet-pink: 15x15x1,5 used for holding the seat for example
purple: flat bar 20x3 used for holding the battery
yellow: flat bar 40x8 used for dropouts

There will be 1mm or 1.5mm thick aluminium sheet metal all around the frame as a cover.


My question goes to those who have experience with custom frames: Which sizes do you recommend? I think I overdid it in my design.

 

[MadRhino]

Estimate the weight of it, then you will be able to decide how much is too much. :wink:

 

[Drunkskunk]

Looks good. A long swingarm like that will run very smooth and stable through the roughest terrain. I used 1x0,5", or 26 x 12,5mm on my build. I think Dlogic used 30x10mm in his, which is very similar to your design. Your 30x15 should be fine.

I think you may run into a stiffness issue with that design the way it is. In Dlogic's build, he welded his side panels in, making them part of the structure and giving him all the stiffness and cross bracing he needs. I think the term for that is a Monocoque frame. With my build, I ran a whole bunch of cross braces and kept the spacing more compact to keep the frame as stiff as possible.

 

[Chuechco]

Thanks for the replies.
I actually thought my design is overkill and there's more stiffness than needed.
I also have aluminium sheet metals all around it, that are bolted to the red frame tubings:

My weight calculation says more than 10kg not inclunding the damper and the brown custom tubings.

How thick are your dropout plates? is 5mm enough?
Can't I reduce the wall thickness of the red main tubes to 1.5mm? What about the big 40x20x2 tubes in the swingarm? They weigh a lot.

Another idea would be to increase the thickness of all aluminium covers to 1.5mm. This should give lots of stiffness all around the frame without increasing weight too much.

 

[speedmd]

I would go 1.5 thick on all of the tubes and sheet. 2.0mm on the swing. If you weld in the skin sheets, you could easily get away with the smaller 20x20 tubing on the main frame and not require much of the little purple stuff other than the bb area and where you want to anchor racks / shelves etc. Possibly some heavier sheet in the head tube and swing mount areas. Drop outs, I would guess should be a minimum of 6mm and possibly 8mm thick depending on size you make them. Hard to tell exactly without some FEA stress analysis, but the sheet will make it super stiff and strong.