&gt; Helmets are very very useful if you&#x27;re riding fast.<p>I can&#x27;t find a reference with a short Googling, but as I recall helmets only help in a fairly narrow window, something like 18-23 mph or so.  If one&#x27;s going sufficiently fast, they&#x27;re unable to do much good (because the forces are too much for a flimsy assembly of foam and plastic to reduce enough to prevent injury or death).<p>&gt; In fact they are mandatory in all cycling sports.<p>They&#x27;re the equivalent of a elephant-repelling rock.