Safe for cars/bikes, or the passengers vs the bicyclist?
Hail comes to mind. Lightning possibly (I believe cars are much better insulated against lighting strikes). High winds could easily push bikes around / knock them over where cars just keep going.
We drove our van through a forest fire (Cedar Creek Fire - a BIG one) and got a bit of smoke, but otherwise, just fine. No way would I have attempted that on a bike - the increased aerobic activity alone (to say nothing of embers / ashes / etc) would have probably caused crazy amounts of smoke inhalation / death.
And there is a reason drivers hate SOME bikers - here in CA, many simply refuse to follow the rules of the road. My light turns green, and 5 seconds later, some biker comes rolling along in the perpendicular direction - I almost hit him. This kind of stuff happens over and over. I am very fond of bikers when they follow the rules - I bike sometimes too.
