Originally Posted by
TomD77
"They provide a crushable structure around your skull that gives your head more time to deccelerate in a collision--"
As a structural engineer (but not exactly my field), my first guess as to the primary rational behind helmet effectiveness isn't lessened G force as much as load distribution.
You may have a point here as far as their success rate in the field goes. The testing is a drop test with a weighted head dummy and the pass/fail criteria are acceleration based if I understood and remember the online information correctly. The design criteria come from testing that British researchers did a good while back using cadaver skulls. They came up with 500g as the maximum acceleration a skull could endure in an impact to guarantee that a fracture would not occur. Over the years this has been reduced to 300g and that is the test standard used in cycling helmets today.
Instrumented American football helmets have shown that a lot of concussion occur in the 20-100g range but there is data and theories to match it to support the notion that rotational accelerations are also important in concussion prevention. Load distribution could have a significant impact on skull fractures, I would suppose. I doubt that it will affect concussion rates but I am an electrical engineer and neither a mechanical engineer nor a medical professional.
Ken