Actually, I think that is a lag bolt. Anchor bolt? Something. But something that cut the casing of my tire down in a hurry.
Thankfully, I always carry a pretty sizable boot, made from a section of old tire, and it did the trick to get me to work.
Just to prove these Tacoma streets ain't messin' around, it also finished off my front fender, and I noticed a bolt for the rear one had rattled out. I am certainly looking forward to getting full metal fenders on the 2010 Clubman.