juchin

I've been hunting for a higher-end mixte frame on craigslist for a long time. I finally found one, but I have nothing to confirm the type of tubing that was used to make the bicycle, since someone removed the sticker. Based on color and size and some corresponding parts, I think its a '78 or '79. The trouble is that none of the parts match identically with the model from each year. I have pivo handlebars, a motobecane stem and crank, an SR seatpost, suntour shifters and front derailurer, and weinnman 999 brake levers. The tires are 700c's so I don't believe they were original. The color is gun metal grey and its a 21" frame. The odd part was that there was a 1975 sticker on it, but based on the color and make, I don't think it matches with a '75 model or anything earlier.

Its a grand touring. I've attached pictures that the seller originally sent me, but I can post some more. It has a dropout for the real derailurer and holes with screws in the rear to adjust the placement of the rear wheel. I have a few bicycles with 531 tubing and I do feel like this bicycle has nicer tubing compared to other mixtes that have been in my possession. I'm guessing its vitus 172. I'm planning to do a 650b conversion, if anyone has any suggestions for me. I couldn't find a motobecane mixte 650b conversion online for some reason.

non-fixie 

Looks very much like a '79 Grand Touring. 3 tubes of Vitus 172. Wheels may be later replacements: those look like Weinmann concave rims. Originally it had 27" Pellet's in '79.

loose spoke

I agree with non-fixie on the vintage and wheels.
A thought...
The most popular reason for 650b is to gain tire and fender space. This frame already has plenty of room for fat tires and fenders in 700c. I'm not sure, but I think there is a better selection of tires in 700c. I've put 700x38 on the diamond frame version. I think it could have taken 40mm and bigger, but not with fenders.
I suppose there are other reasons for 650b, including maintaining frame height off the ground with fatter tires, and of course to experiment with 650b.

Bianchigirll 

Looks nice

juchin

Yes, its going to be my first 650b experiment. The frame is slightly larger for me. I'm only 5' 2" but can ride the bicycle comfortably. I wanted to try 650b because I've read they fit smaller bike frames better and may help with the toe overlap. And yes, I'm looking forward to the cushier tires.

juchin

Thanks for the confirmation. Is there a reason why the parts don't match up with the catalog exactly?