im planning to change the stock 205/55/16 tires of the civic to a 17" or preferably an 18" one. problem is im not sure what tire size is best.

using the tire calculator at http://www.miata.net/garage/tirecalc.html , it seems that using a 205/45/18 tire was the best fit but i checked at www.tirerack.com and found that no such tires were being sold.

the available tire was a 215/45/18 one. will this size fit the civic ok? another choice was to go 215-235/40/18 but im worried that the tire might be too thin given the numerous potholes here in the metro.

what do you guys think?