Driving down a city street at about 25 or so, didn't see it, but must have clipped the chunk of leaf spring with the front tire, and it impaled itself into the rear. Kinda pole-vaulted the back end of my Jeep up and then right back down, sounded like a bomb went off. The chunk of leaf went straight through the tread, and through the wheel.
Lucky for me, I had a full-size, matching spare wheel (and a friend with a spare steelie for the time being). I've never seen a wheel break like that, and I'm just glad I wasn't going faster.