Am I right in thinking 225/40 18 tyres are the usual size used replace 215/45 17 on a blob eye WRX?

I have been doing some calculations and by my reckoning a 17" wheel with 215/45 tyre should theoretically make up a rolling circumference of 137.55cm, and an 18" wheel with 225/40 18 tyre equates to 133.20cm.

A 235/40 18 combo gives a circumference of 137.20cm, if my calculations are correct, so this should be the ideal tyre size?

Anyone know what size rim width is needed for a 235 section tyre?