[JesseK]

It turns out that yesterday's markings faded or were vacuumed up before today. We think there there's an oily residue on new black tires. There wasn't a lot of driving today, so I don't know if the lack of marks at the end of the day was due to that or to the oil having already worn off. We're investigating biodegradable cleaners that don't soften, weaken or otherwise damage the tires Hopefully I'll have more to report by Thursday.