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Dimensions of downtubes of folding bikes

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Dimensions of downtubes of folding bikes

Old 06-03-11, 03:24 PM
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ukebert
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Dimensions of downtubes of folding bikes

Hi all,

It with a twinge of this guilt that I join this forum expressly to ask people to help me out with one particular thing. I am currently doing a project at University on the influence of shape on the downtube of step through frames and am stuck for data.

What I need is the shape of the tube (i.e. circular, oval, square, rectangular, etc.) and the dimensions, both internal and external. Obviously getting internal dimensions is a little tricky without taking a hacksaw to the frame, but for a folding bike it should be possible. The folding bikes that I've seen generally hinge on the downtube and you can see up the tube. So it shouldn't be difficult to get the internal dimensions of the tube. The external dimensions should be straightforward, after allowing for the flange at the hinge.

Hopefully there are a couple of people who have a folder which they are willing to measure for me, it would really help me out. I've emailed some manufacturers, but n joy yet and the deadline is at the end of next week (typical disorganisation on my part I'm afraid).

Thanks in advance and sorry for breaching internet etiquette, I hate it when someone joins one of my regular forums just to ask something like this!

Regards,

ukebert
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Old 06-03-11, 06:43 PM
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rhenning
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I have about 20 different folders. Everyone of them had some variation on/in the down tube except the 3 Raleigh 20s. Two of Raleigh's fold and one doesn't. Some are round, some are oval, some are double and on and on. There is no answer to your question. Roger
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Old 06-04-11, 12:33 AM
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jur
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Perhaps you should head to a bike shop that has some different brands for you to measure.
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Old 06-04-11, 03:55 AM
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ukebert
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Originally Posted by rhenning View Post
I have about 20 different folders. Everyone of them had some variation on/in the down tube except the 3 Raleigh 20s. Two of Raleigh's fold and one doesn't. Some are round, some are oval, some are double and on and on. There is no answer to your question. Roger
Ah, a slight misunderstanding. I understand that different folders will have different shapes, that is the point! I'm looking for lots of data from different bikes. This is a fairly approximate analysis, so if there is variation on the downtube (which I understand that most would) then the point at which it hinges would be fine. Double tubes are also fine, I'd just need to work out the second moment of area for them, so I'd need the distance between them as well as their principle dimensions.
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Old 06-04-11, 09:06 AM
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Is it useful for you to have only the OD without the ID? If so, I can send your a data point for one bike (Brompton).
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Old 06-05-11, 08:06 PM
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ukebert
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Originally Posted by kamtsa View Post
Is it useful for you to have only the OD without the ID? If so, I can send your a data point for one bike (Brompton).
Unfortunately not, I need both internal and external dimensions to make any sense of the results. Thanks for the offer of help anyway.

I'll try going out and measuring at bike shops this week, but time is horrifically short on this report and I'm worried about getting enough data.
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Old 06-05-11, 09:38 PM
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Another complicating factor is the fact that a lot (most?) quality bikes use double butted tubing - Bike Friday does, and at least some Dahon models do, for example. So measuring where the downtube hinges (if the downtube hinges; they don't on many folders) won't give you the proper measurement for the tube unless it's a straight-gage tube.
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Old 06-05-11, 11:39 PM
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To know wall thickness , of built bike tubes, you have to cut them up..

try the police auctions, and scrap yards, for victims.

or do a lot of travel and visit manufacturing sites
China, England , Oregon

but it sounds like the term will end 1st.

Last edited by fietsbob; 06-05-11 at 11:45 PM.
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