A vacuum intake horn is constantly secured to a portion of a land vehicle and connected to a vacuum generator to increase the load on the wheels and, thereby, enhance traction. In order to minimize the clearance between the intake horn face and road surface for greater vacuum force, the vacuum intake horn is attached to a portion of the vehicle such that movement of the vacuum intake horn relative to an associated wheel of the vehicle is no greater than 75% of the movement of the vehicle chassis relative to the wheel. The vacuum intake horn is mounted behind and substantially entirely within the outline of a tire, so that the tire protects the vacuum intake horn from debris and bumps in the road. In one embodiment, the vacuum intake horn is attached to the vehicle by a compensation arrangement that maintains the vacuum intake horn at a generally constant height close to the road surface despite tire deflection or movement of the chassis relative to the associated wheel.