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Motobecane seat tube oddity

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Motobecane seat tube oddity

Old 05-18-23, 05:04 PM
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Motobecane seat tube oddity

I just noticed that an upper section of the seattube of this recent aquisition (a Jubile Sport) has been reduced in diameter.
I think that explains the smaller-than-expected seatpost, it's a 26.2, and the seattube - where I first measured it - was 28.8 (+ paint,), so the wall thickness would have been about 1.2.
That doesn't ft with the catalog specs (at bulgier.net) for this date Jubile Sport, which say Vitus 172.
The reduced portion has an od of about 28.4 (+paint), so that makes a wall thickness of 1.1mm at that portion (which would be thicker because of the reduction).
This frame had no tubing sticker; the forks says Vitus 888.
What is also odd is that the reduced diameter portion fits nicely into the seat lug:




This bike is odd in several other ways - the decals are not a real match for any of the the catalog models, the wheels are Normandy with Rigida rims, the mechs and shfters are Huret; it all fits, and it looks original...
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Old 05-18-23, 07:01 PM
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I agree it does appear to lessen towards the lug.

Hows does the slot of the seatlug look when in full pinch? Does that look reduced? Does it hold position? Is it supposed to be 26.4?

My initial thoughts are if it's not broke don't fix it.
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Old 05-18-23, 07:05 PM
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Pretty common on entry level French bikes back then. I think my 82 PH10S had the same thing...... IIRC, the seatpost on that bike was really small diameter too.
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Old 05-19-23, 05:37 AM
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Originally Posted by Mr. 66
I agree it does appear to lessen towards the lug.

Hows does the slot of the seatlug look when in full pinch? Does that look reduced? Does it hold position? Is it supposed to be 26.4?

My initial thoughts are if it's not broke don't fix it.
Slot is good and I am pretty sure *everything* on this bike is original.

No fixing involved or anticipated - just an oddity.
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Old 05-19-23, 05:58 AM
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I don’t think I’ve seen that before. I have a Gran Jubile and a Grand Sprint and neither have it.
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