That is the question, isn't it?
I'm curious why you chose 18" instead of the more common 17" and 19" or the more lightweight and size-appropriate 21"?
I have considered 2.75-21 and 3.00-21 tires before (though improvements in the size range of available bicycle tires have turned me away from that approach), but having had a motorcycle with an 18" wheel before, I just can't reckon what's the appeal.
As I recall, Dunlop K591 tires were sticky, widely available in less-common or archaic sizes, and seemed to work great unless you had lots of power (in which case they wore out too quickly). They're really old news now, but I'm sure they are still available.