Tyres.co.uk lists options for the factory 17-inch wheels on the 2011 to 2018 Focus. Michelin Primacy 5 and Goodyear EfficientGrip Performance 2 215/50 R17 are the options available. Make sure to examine the load index, speed rating, and any XL construction on the registration.
To check the tyre size of your Ford Focus, look on the B-Pillar on the driver's side inside the door. You will find a placard with the approved range of tyre sizes and the load range and cold pressure of the tyres as well as the pressure of the spare tyre. The fitted size is indicated on the sidewall of the tyres.
On front wheel drive Ford Focus models, you can replace all tyres on the same axle, in pairs, only if the new tyres have the correct size, load, and speed rating. The new tyres should be fitted to the rear axle. For Focus RS all wheel drive models, all four tyres should be the same, with no mismatching.