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 degrad

In regards to safety, the full-face helmet is the safest choice of the Four. The full-face helmet offers the most coverage surrounding your head and neck. A full-face helmet protects you from the environment you're riding in, whether it be inclement weather or debris and bugs hitting your visor