The Like 150i uses a 110/70-12. The Vespa Sprint uses the same size but the bigger Vespa's use a 120/70-12. The City Grip comes in a 120/70-12 but not a 110. At least I haven't been able to find it in the USA. I'll bet it is offered in other parts of the world. The Michelin Power Pure does come in a 110 so that's probably what I will use when I need a new front tire.
I'm sure a 120 would fit on the 150i but using a different tire size may confuse the ABS so I'll stick to the stock size.