Originally Posted by prosgal73
do you recommend the servotronic if you go with the 18 inch? i didn't like the feel of the servotronic with the 17 inch-too loose
If anything, Servotronic should help, as it reduces the power assist as the speed increases.
The choice is only available for the xDrive 28i:
sDrive 28i: Electronic steering
xDrive 28i: Hydraulic steering, Servotronic optional
xDrive 35i: Hydraulic steering with Servotronic
If it's too light for your liking and you mainly drive at low speeds, you can probably get the wheel alignment adjusted to reduce the camber angle. This will make turning at low speeds slightly harder, and buy you a small amount of grip in good conditions.
(Perhaps the 17"ers had been put on without the alignment adjustment needed when changing wheel sizes? That would explain the difference.)