I drove the car on 205/55/16s and it handled really well, the tyres had plenty of grip and there wasn't much body roll; and this was at Donnington Park so I was really pushing But with 225/40/18's there is NO additional grip, it handles exactly the same when it shouldn't. It should handle noticeably better, the tyres are good, the PSI is correct and the suspension is in good working condition. Its a bit slipperly in the wet but that could be down to the make of the tyres.