Anything can go anywhere with enough effort, having the right chassis/tyres for the terrain just makes it easier. In the case of the Hornet, what you've got is a sweet road chassis with not much ground clearance and fairly stiff, short travel suspension. That's great on tarmac, but it's not going to be quick on unsurfaced roads for more reasons than just the tyres.
Now, if you were to shoe-horn a knobbly tyre onto each end of it and sort a front mudguard to clear the knobbly front, you'd maybe give it a bit more traction on slippery stuff, but you'd not have the chassis to really capitalise on that as you'd still be nursing it along trying not to flatten the exhaust or ruin a wheel on a rock, or catch the side of that inline four on the edge of a rut. Basically it'd still have insufficient ground clearance and suspension travel for the rough stuff. You wouldn't be able to fit a 19 or 21 inch dirt wheel in the front because it wouldn't clear the radiator/cylinder head/exhaust headers when the suspension was fully compressed. Unless you changed the forks, too...
Plus a Hornet on knobblies would no doubt handle like a wonky shopping trolley on tarmac, and you'd have to be on acid to want to put longer trail bike forks in it. Either way, you'd have ruined what the bike is very good at.
The rear rim is probably a 5.5in width if the standard tyre is a 180 and you won't find a knobbly tyre wide enough to suit, so you'd be engineering an alternative rear wheel. When you got to Oz and wanted to turn it back into a road bike, you'd have to get another rear wheel to put the road tyres back on.
So, if the Hornet is the bike you want to do it on, my advice would be to do just that, but you should play to it's strengths (tarmac) rather than make it into something it isn't. You can get a very long way on mostly tarmac, and whilst the distance you do have to do on dirt to get where you're going may be really hard work (it's also a heavy bike to pick up) you would find a way if you wanted to. Meanwhile you may well have been having more fun on the tar roads than any trailie could.
If it were me however, and I didn't want to be constrained to the tarmac routes, I'd just take a trail bike of some description instead. Then when I got to Oz, I'd buy a road bike if that's what I'd rather be riding for the year or two I was there.
'02 Africa Twin (sold), GSX-R 1000 K5 (sold), '97 TL1000S, '08 DRZ400 SM/S, '92 CRM250
Last edited by djadams; 9 Jan 2011 at 13:00.
Reason: spelling, punctuation and grammar.