Originally Posted by 4corners
If it's only during hard braking (but smooth on cruising), then obviously, it's most likely brake related rather than anything to do with wheels, tyres or suspension.
ABS pulsation is quite obvious as you can feel (through the pedal as well) and hear the high frequency blunt knocking noise as the ABS pulses.
I would start by having your brake discs checked for excessive runout at your dealership or reputable mechanic. There is a good chance that your discs are/have (one or more of the following):
1) not sitting flush and flat with the wheel bearing
2) uneven pad deposits
3) warped due to wear and uneven skimming
Note that spacers and larger/wider wheels/tyres will exacerbate any form of vibration around the wheel area, due to the fact that the wheels (+ extra weight) are further out of the car, which increases the effect of centrifugal force on the spinning axis.