Originally Posted by MikeBMT
The easiest way to do this is with a 'Hit Trigger' (Second item in Trigger menu)
You will then also need the 'Bike Part Detach Event'
Place the hit trigger and the Detach event, go into the properties for the Detach event and hit 'Select Bike Parts' - Then select what bike parts you want to detach, In your case the front and rear wheels.
Now go into the Hit Trigger properties, You can leave Hitting Objects 1 alone, as they will be default to the bike/rider. Pick Set Hitting Objects 2, make sure everything is unchecked, and choose 'Select Object Instances' and then simply select your wrecking ball. Back out of that menu and in the Hit Trigger properties window, click on 'On Hit' and select the Bike Part Detach Event.
You're done!
When you have this all set up, there should be 4 lines. A blue line going from the Wrecking Ball to the Hit Trigger event, a Red line going from the Hit Trigger Event to the Bike Part Detach Event (This is the key, when the wrecking ball hits the rider, the impulse will be sent through this red line and activate the bike part detach event) and two blue lines from the Bike Part Detach event; one to the front wheel and one to the rear wheel.
Hope that helps.