Originally Posted by
melville
Bags that size were intended to hold spare sew-up tires. 40 years ago, some people were still touring on sew-ups!
The bag was intended for use for spare tubulars (aka sew-ups), as noted. I've still got one that I use, and it's quite a civilized way to carry a spare tire. It even has a little zippered pocket for a couple of small tools. This was back in the days when Cannondale was a bag manufacturer, and not a bike builder.
Here's a shot of it on my Olmo, which was fitted with tubulars at the time.
Steve in Peoria