Can't get tyre on / Tight rim

Don't be tempted by Continentals. If Vittorias are tight then you've a snowball's chance in hell of getting a Continental on.

Michelins are usually pretty easy to get on most rims.

but different batches/models of tyre can vary even from the same manufacturer.
i have some GP4000s that go on easy but some grand-prix's that are a pain