Wan e46, just want to share some of my experince with u:
Initially my ride was on 18" with front 225/40/18 n rear 255/35/18 RFT tyres, fuel consumption in KL city drive was crazy high at 12.7 L/100km. Stock BMW Style 72 wheels and very bumpy feel.
Then adhere my trustworthy guru Mr. Yau advice, I DOWNGRADE it to 17" with front 225/45/17 n rear 245/45/17 Non-RFT tyres, fuel consumption in KL city drive instantly drop to 12.4 L/100km. Stock BMW Style 68 wheels and drive was much more comfort.
Recently I changed wheels again to ori German BBS RX wheels, using back the initial 17" with front 225/45/17 n rear 245/45/17 Non-RFT tyres, fuel consumption in KL city drive instantly drop to 12.1 - 11.9 L/100km and guess wht? Road handling even better!!!