Originally Posted by
Narhay
I will do some digging once I am home and see if I can find any numbers.
The reynolds decal is certainly boom era as mentioned. The decals are the same as my 1972 px-10 except there is only one fork decal on the drive side and it has reddish font instead of the typical green. Maybe a French way to save half a cent per bike or it has been lost along the way.
I have also potentially found a damaged stem bar clamp after reviewing pictures this afternoon. Undersized French diameter bar and overzealous clamping?
Red 531 versus green 531 is indicative of 531SL (Special Lightweight). This was an even thinner gauge of 531 favoured by some French manufactures for their pro racing models (i.e late 1970s Peugeot PY10). However, you said it has a 26.4mm post which is indicative of 19/22g seat tube, which is the heavier of the two options for the butted 531 set of the era. Had this been 531SL, the seat post would have been 26.8mm