i know this belongs in wheels/tires but it's dead over there.

question: how does a nail go into a tire? wouldnt the nail be flat on the ground? even if it is standing up, how would it have just the right angle to go into a rolling tire?

 

roofing nails are the most common culprits in my experience, where the large head and short shaft make a perfect tire sticker. The tire stands the nail up and the shaft punctures the tire.

I had long decking screw in my tire last summer. I'd say the same mechanic is at work, as your tire IS rubber, and deforms around the nail/screw while the tip punctures and sticks in the tire long enough to get driven home the next revolution.