Originally Posted by
njkayaker
It's for another water bottle. Though what actually works depends on your frame size and fenders. You might be able to use a smaller bottle.
The bosses for a third water bottle are traditional/customary for touring bikes: it's how you know a bike is a tourer!!
Some tourers carry fuel for their stove there (where the fuel won't do too much damage if it leaks).
Haha, yeah I know that. The problem is, well, see above. If I could find a small enough bottle, I would use it for its intended purpose.
Thanks for the idea willi, but my frame pump is offset so as to not interfere with the cage...leaving the cage empty!