YES that is old tire dressing sludge!!!
Everyone loves the look of freshly dressed tires, it really completes the look of the entire detail. However, not all tire dressings are created equal. Most people who use tire dressings are aware of the dreaded sling some of them produce, but the issues don’t stop there. This sling off can actually stain paint and plastic parts if left long enough. More importantly, tire manufacturers add antioxidants and antiozonants to the sidewall and tread to help prevent premature aging from ozone and weather exposure. Certain cleaners and tire shines can remove these important components of the tire which can lead to cracking and sidewall failure.