In a crash, a good helmet limits the shock transmitted to the wearer’s head. These limits, generally expressed in G’s, multiples of gravity, are comparable for M2010, DOT and ECE 22-05. The critical difference for M2010 is that helmets must continue to limit the shock for much more severe crash impacts.
When a rider crashes, there’s no telling what he’s going to hit: a broad, flat roadway maximizing the contact area with the helmet or a shaped surface which will concentrate the loading to a small portion of the helmet shell. Broad flat surfaces produce higher levels of shock immediately but load concentrating surfaces may collapse the helmet wall and then transmit uncontrolled levels of shock directly to the wearer’s head. A good helmet must be able to contend with both types.
A crash impact might fall anywhere on a rider’s head. Good helmets, as much as possible, will get between the rider and reasonably likely impacts to provide protective coverage. M2010 and DOT specify test lines and allow test impacts centered anywhere on or above those lines. ECE 22-05 specifies the test impact locations directly.
A good stiff outer shell is essential if a helmet is to protect in impact against load concentrating surfaces. Helmet shells must be also tough enough to resist penetration by edged and pointed hazards such as road side barrier structures, signage, foot pegs and much more. Shell penetration testing and edge impact testing assure that the helmet shell will do its part.