Might be best to re-purpose a seat bag as rack top bags from all the usual suspects are around 30cm and up. I was surprised that their aren't any in the size you want.
Yeah, you're probably right. The Vaude Silk Road S(mall) is about right but I'd quite like something fairly classic so some sort of carradice is probably the answer.
Yeah, you're probably right. The Vaude Silk Road S(mall) is about right but I'd quite like something fairly classic so some sort of carradice is probably the answer.