Check out the available tyres too. With a full on trail bike it's easy, they all have spoked wheels and you can get anything from a slick to a sand tyre in a TT fitting. Get a puncture and the worst case is an hour with hand tools to get a patched tube in. A 21-inch motorway tyre is rare but you can live with a middley knobbly set up on most runs. Wear one out and every dirt bike shop in the world can sell you something even if it is often a bit extreme.

With alloys you are limited to TL fittings so depending on the bike will probably get a choice of slicks through to fairly knobbly multi-use. You won't get a 17-inch TL sand tyre though.

The F650 single though had an issue when launched. The rim sizes, swing arm clearance and spoked wheels used a TL tyre to get the tread pattern they wanted and fitted a tube to cure the spoke leaks. No one made a TT tyre that fitted as a pair. If you had a puncture it was impossible to plug from the outside or get the tube out using hand tools. Various chain gang members had various torture type devices along the lines of bolt cutter and extending ten foot pole sized things that could break a TL bead but I never fancied carrying them as they were bigger than my tent and heavier than the rest of the tool kit. The only remaining solution was tyre gloop of some type. Basically you were starting off in limp home mode.

I think this has now been cured as Bridgestone and Heidenau do TT tyres in road or semi-knobbly types although last time I bought some I had to wait a while. Check on the Chain Gang site as I'm going back close to 8 years now, I only remember the tyre sizes and have been buying similar for the Bonneville. You won't find these exact selections in many bike shops and may find BMW dealerships are probably still banging TL tyres plus tubes on.

Andy