From a safty point of view spacers on the front are a very bad idea as is will impact the scrub radius. The front suspension geometry is designed so that the SAI intersects the road outside the center of the contact patch of the tyre, so that in the event of a puncture the drag on the wheel counter steers the tendancy to turn to flat. Putting (more than 5mm) spacers on reverses this so a flat will have a more pronounced effect.