Tire sizes
 

I've been a technician for over 11 years, done thousands of tires, among everything else but ran into an issue yesterday(Friday)that I've never ever seen before in my life. I certify used cars to go out on the lot for sale at a dealership and I got a 2008 Volvo C70. The tire placard says size should be 235/45/18 but the the tires on the car are 235/40/17. On the car, The wheel is an 18 but the tire is a 17. Measured the wheel from lip to lip with measuring tape(not on balance machine) and it's an 18 inch wheel! I'm dumbfounded, as well as 3 other technicians in the shop. Can someone clarify this for me? Please and thank you!

are they OEM wheels? What's stamped on the wheel? OEM sizes the for the C70 are 235/45/17 or 235/40/18 on an 8 inch ET45 wheel. That said somebody could have bought an off size, ie 235/40/17 but there's no way a 17 inch tire mounts on an 18 inch rim so somethings mismarked.

If it measured lip to lip 18 inches then it's a 17" wheel. You measure the bead diameter.

If a 17" tire fits, then it's a 17" wheel, in other words.

Yes they're OEM. But like I said the door placard says 18in the wheel measured from lip to lip is 18 in. but the tire itself says 17in. The cars are trade ins and I never get to talk to the customer or know where it came from.

the door placard simply suggests a manufacturer's suggested (minimum?) tire pressure for OEM wheels - which can be either 17 inch or 18 inch for the C70, but that's not to imply what came on the car. For example, on my 850 the placard shows 15 and 16 inch wheel pressures but the car came with 15s.

The door placard shows tire pressure for both 17 and 18 inch wheels