I can't give you a definite answer on hitting a tree at 40mph, but the hit air airbag vest has been tested by Jari in state of the art testing labs. Here is a video that shows how the vest performs in chest impact. With even a full conventional chest protector the deflection is 52.1mm With the hit air vest the chest deflection is less that half of that 20.7mm That is quite a difference. Here is the video: Here is some testing and demos of Helite vests. the demo a about 30s shows how fast the system is on a test rider hitting a car in a typical left hand turner situation.