Bicycle Helmet Safety Institute explores this in detail, and points to other resources. Short answer:
* Did you crash it? Replace! * Is it from the 1970's? Replace. * Is the outside just foam or cloth instead of plastic? Replace. * Does it lack a CPSC, ASTM or Snell sticker? Replace. * Can you not adjust it to fit correctly? Replace!! * Do you hate it? Replace.
Longer answer, rationale, and more links are at:
http://bhsi.org/
Now, if you change the question around a bit, you can ask me what risks I take for myself. 1) In general, I ride with a modern helmet. In my case, a Bell Metro. As Larry Black pointed out, it doesn't look like a fantasy item from Star Wars or something. It is easy to adjust, except for the neck strap.
2) I have a few 1970s helmets. Fortunately, some don't fit, so there is no temptation to ride with them. However, I have been known to wear an early Bell or my slightly later foam "Paramount" at Cirque when I'm riding in vintage jersey and shorts. Maybe 25 mi. of my 4000+ annual miles, or less than 1%. Maybe even this is a foolish risk, but I'm willing to accept it once a year.
Harvey Sachs McLean VA Not guilty of doing quantitative risk analysis. However, I do feel that economics is the study of the price of everything, but the value of nothing...
Bob Freitas wrote:
> HARVEY
> this thread has finally moved to the point I am interested
> in #1 just how safe are older style helmets(I am not even thinking of
> "hairnets" here)
> for us who have old BELLs or FOAM type GIROs hanging in our
> garage just how safe are they? #2 for us riding with newer helmets
> like LIMAR etc is there a deterioration of safety as they age? (DALE,
> I feel this is VERY ON TOPIC as we are trying to protect VINTAGE BRAIN
> PANS.) I know the standards for MC helmets are updated for time to time.
>
> BOB FREITAS
> sunny MILL
> VALLEY,CA
>
> as an aside ,a few years back I did a weeks worth of
> cycling around the SAN JUAN islands sans beanie or"DO RAG" under my
> ventilated helmet
> the end result was an interesting Tan pattern (think DARTH
> MAUL) I got a lot of strange looks in my civilian clothes til it faded.