Bear in mind that if the helmet did its job most people would tell you that they did not even hit their head, or did not hit their head that hard. And the thin shells on most helmets now tend to hide any dents in the foam. But if you can see marks on the shell or measure any foam crush at all, replace the helmet.

The bottom line: Leaving your bike outside for a day or two won't do major damage. You may see signs of rust after a week of neglect. After one month in bad conditions, your beloved bike parts will start to degrade.

The first rule of bike safety is: be aware of your surroundings. The second rule of bike safety is: make your surroundings aware of you. Never be a surprise. You never want to make a motorist say 'he came from out of nowhere, officer. I didn't have time to hit the brakes.' That's when you die, or get injured severely.