Front tyre on back wheel?
 

I'm in Africa and seriously stuck for an 18" back tyre but can only find off road ones (I'm going to be on road all the time) or a 18" tyre that says "front use only". What would be the problem with putting it on the back? Would it be okay as a temporary solution?

I believe you'll need to run it 'backwards' so the tread will work effectively, but you don't want to be doing too much speed.

Is the loading rating high enough?

Is it wide enough to fit the rim?

Tubed or tubeless?

How far are you going - is it worth getting something shipped in?

to add to the previous message, there is a difference in profile between front and rear tyres, to take it to extremes we ran a cbr600 race front on the rear of a 125 race bike, the handling was a little "odd", the rear used to drop in a bit quicker than the front, giving an effect of pushing the front wide, or understeer, but not dangerous.
It will wear out quickly, as the carcass isn't designed for central wear.

Thanks guys, it's to be used as a spare replacement for the old one I have on at the mo - I'm going through Mauritania and Western Sahara (main road all the way) so don't expect to pick anything up en route. Won't be driving fast either. It's tube type, I will check load rating. As for getting something shipped in, if I had the time and/or money...