These extension bricks will be full bricks ie for 2x2 bricks these are changed to 3x2 bricks. Special Bricks are used for this that attached to the bottom of the car and hold it firmly in place. The LEGO Group does not sponsor, authorise or endorse this item nor any of the customised/modified products or sets shown on it nor does it accept responsibility in any way, shape or form for any unforeseen and/or adverse consequences following from such customisation/modification.
eBay