Bridgestone RE003 bloody good too - very grippy wet or dry, maybe not so long lived though, still reasonable life for the $ according to others.
As I understand it, all else being equal, wider rubber with lower profile tyres creates a wider but shorter longitudinal (front to back) contact patch. The higher air pressures necessitated by low tyre side-wall heights means of the tyre touches the road less longitudinally.
Conversely, the lower profile wider tyre has less heat build-up to dissipate (due to less sidewall flex as well as wider tread for cooling) so can be made of generally sticker/softer and therefore grippier rubber. Ride quality suffers of course due to less absorption available in the smaller sidewall.
But a wider contact patch means some better lateral grip at the expense of less braking/traction grip - mainly because the lower sidewall flex makes for higher slip angle (point where tyre bends away from the road under lateral load).
But really if you are just going from 215/45/17 to 225/40/18 it probably stuff all difference longitudinally and the rubber softness will have much much more impact on grip. 5% wider, 8% shorter sidewall.
Good read here:
http://www.carbibles.com/tyre_bible_pg3.htmlAnother factor to help increase grip is to drop air pressure a little to fatten the contact patch - try that first.