I've got ghe full size BMW tank bag. It came with my RT and IMO it's far too big. Just gets in the way. Used it on my 1st European sortie a couple of years ago as I thought it would be handy to have somewhere to put the Euros for the Péages. Nowt but a nuisance, never again. And it wasn't waterproof either. I would, however, consider a smaller, flatter option.