frank, there is free play if using normal seatbelts. During hard braking, you will be thrown forward, the seatbelt thing will only hold you up after it detects a fast release of belt. That's why can feel chest pain cause it is sort of like hitting the seatbelt.
For racing harness, if held down tightly and properly, the person won't "hit" the seatbelt plus the force acting on the person's body is divided into 2 straps of harnesses which will distribute the force all over the entire harness rather than the single normal seatbelt.
the article your sifu gave.... freaking 73 pages....
true also......
whahahaha, thats why i said i didnt bother to read. 73 pages. whahahaha... anyway i did read a couple and fast flip thru some pages. It seems like to be in order for harness to work as it supposed to be, alot of factor need to look into it. If u read some pages, it seems like user height and shoulder broadness play crucial factor