I've been looking into a set of winter tyres for the mond as I don't fancy forking out for a 4x4 just for the winter!

My question to the good people of PF is about rolling circomference. Basically, I'm going to put the winter tyres on a set of standard 16'' steelies as they are easier to swap over in the winter and they'll cost less than the 18'' equivalent.

The car is currently running 225/40/zr18's....What size tyre would I need to keep the rolling circomference near enough the same?

I'm told a 205/55/16 will do the trick?

Also the tyres I've been looking at are continental contiwintercontact ts830...They have been getting good reveiws on all sites but has anyone had experience with these or any other winter tyres?