Our tandem is an older mountain style, it has 7 speed set up and I want to upgrade some stuff. I was curious if you could switch out the 7 speed set up to an 8 or even a 9??? I know there can be issues with the space on the back hub but I don't know how limiting this is? The shifters are klunky and I'd like to get rid of them. We really love the bike but its needing some upgrades so we can use it for years to come. I am figuring we will need new cables throughout and maybe new derailleurs too? Fortunately I can get some pretty sweet deals on parts but I'm just hoping I can make an 8 or 9 speed set up work? Anyone have experience with this sort of thing?