Hi Engineer: Minor differences come to mind. I have a skinny 21" front end on my 20 year old H-D softail custom and I'd say the skinny tyre gives lighter and more precise steering (for that bike anyway) as there's less rubber on the road to fight with, especially at slow speeds. You could also think of the reduced unsprung weight but I'm not convinced that would be significant unless the fat tyre was really FAT! A drawback could be that the skinny front tyre doesn't help to "self-balance" the bike in the way a fat front tyre would. Years ago, in Canada, I took part in a H-D riding competition, at a rally, involving fast figure of 8s, 90º turns, multiple s bends and a slow section. The slow section was trickiest because of the skinny front end whereas a fatter front tyre would have balanced itself easier. I did it on my bike and then my wife's heritage (much fatter front tyre) and I was much slower on hers. I came second top and the guy who won, also won it the year before, on the same bike as me - a softail custom with skinny 21" front end and a 34º rake. Unfortunately, this doesn't relate too much to the road but it's a good reference.