Helmets are generally designed to handle the vertical component of the fall, not your forward velocity.<p>If your torso hits a solid object at 30mph, there&#x27;s about ~50% chance you&#x27;ll rupture your aorta[1]. Hit something like a narrow signpost pole at 30mph and you&#x27;ll be in a whole world of trouble - I&#x27;d post a link to a thread on a motorcycle forum, but it&#x27;s a bit grisly. Guy survived, but he had to be opened up to treat the internal injuries.<p>Motorcycle helmets have mostly the same minimal impact requirements of preventing brain injury from the vertical component, but also need plenty of abrasion resistance.<p>[1] I heard this on London Met police BikeSafe day, a day-long course where London police do a presentation to motorcycle riders and go on an ride with a police observer. But for specific reference, see <a href="http:&#x2F;&#x2F;www.nhtsa.gov&#x2F;people&#x2F;injury&#x2F;research&#x2F;pub&#x2F;HS809012.html" rel="nofollow">http:&#x2F;&#x2F;www.nhtsa.gov&#x2F;people&#x2F;injury&#x2F;research&#x2F;pub&#x2F;HS809012.htm...</a> - &quot;UK Department of Transport Traffic Advisory Leaflet 7&#x2F;93 (TAU, 1993), figures quoted are, for 20 mph impact speeds: 5 percent death, 65 percent injured, and 30 percent uninjured; for 30 mph impact speeds: 45 percent death, 50 percent injured, and 5 percent uninjured&quot;