Going off-topic real quick, but have you noticed much range loss with 155 on front? Also, what size and brand tires are you using on front (I know 155 wide, but is sidewall 60)? I've driven an i3 with 155 front and 175 rear (though on 19" wheels), and that thing was solid at 65 mph.
I've raced an i-MiEV on Gran Turismo 5, but not in real life. That game is actually how I discovered the i-MiEV.