1985 trek 660 question
 

Picked up this frame yesterday, and I'm searching around and figuring out some things about it. One question though, whats the 72 on the inside of the rear dropouts refer to? thanks.

Could it be the intended Head Tube Angle (unlikely for on the rear dropouts) or the BB drop?

21" and under had a 72 degree HTA, the BB Drop for all sizes was 7.2.

That's the seat stay/chain stay angle. Those investment cast, socketed dropouts needed different angles for different frame sizes and chain stay lengths. That wasn't an issue with the traditional tabbed dropouts, which could accommodate almost any angle.

Other manufacturers of investment cast dropouts used a separate piece for the seat stay socket to accomplish this:

http://www.cyclesdeoro.com/images/In...y/PICT2992.JPG

Thank you!