Will replacing a tire with one size smaller, hurt anything?

FWD Ford Fusion, hit a giant pothole, has a 225 size tire, but the local used shop only has 220(?) he said its one size smaller and he ll throw it on for me until they get a 225 in stock. We can't afford a new $120+ tire right now, otherwise we obviously wouldn t be asking this question. This guy sells nice used ones for $20-$40 a piece installed and balances the wheel as well. I've bought numerous tires from him so I trust his work and word, but would like a second opinion since I've never ran an odd size tire.

The car is FWD, and the tire is the passenger rear.

Never a good idea to have two different size tires on the same axle. Creates extra wear on the differential. You haven't spent money until you repair a differential on a FWD car.

You could put the 220 in the back where there's no differential.

While it's not ideal, it's only a 5mm difference. Realistically about the same as having a worn and a new tire on the vehicle.

On the rear of a FWD car, it won't cause any problems.

Won't hurt anything. Put it on the back.

If it's a 4x4 they need to be same size.