245/45/18 Factory size.. Can i use 275/40/18 on the factory rim? The calculations show the tires are the identical same diameter, but can i use this size with no problems.

 

The complete Wheel including the rim is not wide enough so you end up with a tire rubbing mess especially when you turn or hit a bump. A 255 tire/40 is plenty of rubber for this car.

 

I put 255/45 nitto motivas on 18x8 et 42 voxx rims. No problems with rubbing or clearance, except that I get squealing in reverse on rainy days backing out of parking spaces, so I guess there's really minor rubbing at full lock. Based on that I wouldn't go any wider. I think the 255s look good, doesn't lessen arch gap much but brings the tire to the edge of the wheel well.