Technical & Reference Section > Tech and Restoration
OG fatgoose 170 update
oldschoolace:
I think without having scaled up tube diameters to suit, your build was always going to be prone to a bit of flex. The width of the bb presents a considerable increase in leverage perpendicular to the seat tube. If you can live with it I would put up with the flex unless you have serious concerns about an actual failure of the frame. For me any gussets added around the bb short of a wider square section between the bb and the hoop would spoil the look of the build.
snoopy72:
I spoke to a frame builder and he said if you brace it, it's a bit like sticking a band aid over it, it will only cause a problem at the end of each brace making that part the weakest, he also said the same as oldschoolace that ideally all the frame tubes needed to be enlarged, the only problem with this is you would then have a weak spot at the headstock because you would still have to use a normal size headset and stem.
I think you could go on forever and it certainly wouldn't resemble a mongoose when finished, I'm waiting for more suggestions apart from throwing it in the plastic thing with a lift up lid :LolLolLolLol:
Maybe just extending the rear rectangle a bit would help, this is where it feels weakest and then hope for the best, I certainly know it's not going to be suitable for a table top, I do like hutch bars but don't fancy a face full of them.
oldschoolace:
This might be a total nonsense but would be easy to test. what about filling the tubes with, expanding foam? wouldn't add any weight but the honeycomb structure may help stiffen things up. You could cut yourself two identical pieces of copper pipe, fill one with foam and test it against the other with some weights hung over the middle.
As I say, could be bullshit but could also be a cheap and easy fix :daumenhoch:
snoopy72:
:LolLolLolLol: I'm open to any suggestions at the moment, i'd fill the tubes full of tampons if it worked :LolLolLolLol:
unfornunately the only tubes accessible are the rear stays and seat mast, the rest are sealed.
The flex doesn't seem to be getting as far as the rear stays only the bb area.
I suppose It will never be as flexible as riding a hinged Raleigh Hercules shopper bike with the hinge unclamped
rodriguez:
I think it'll crack where the bb meets the box the way it is under heavy load, in my opinion that's the area pedaling will stress most as power is transferred to the rear wheel via the cranks.
I'd consider increasing the size of the box.
As it would reduce the bb flexing I think this might actually reduce the stress on where the down tube and seat tube meet the bb.
Might increase the stress where the down tube meets the head tube though.
Any structural engineers on here?
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