If my wheelchair has a tilting seat frame, what is the best way to secure the wheelchair to a vehicle?
The answer depends somewhat on whether your wheelchair complies with WC19 or not. For non-WC19 wheelchairs, both the front and rear securement points should all either be on the seat or all be on the wheelchair frame. Choosing securement points on the same structure should minimize the chance for slack to develop in the tiedown system if the seat tilt angle changes during a crash event. If possible, the four points should be on the seat, since these points will usually provide slightly steeper tiedown strap angles that increase wheelchair stability and reduce upward movement of the wheelchair in a crash situation.
For WC19-compliant wheelchairs with a tilting seat frame, the securement points provided by the manufacturer have been tested dynamically, and the wheelchair manufacturers instructions will provide information on how to use them.