Above all, be gentle with it. Don't try to peel or chip it off because you'll likely take off paint at the same time. There are a number of products you can buy that specifically target tar and other sticky substances. WD-40 is often recommended. Most people look at it as a lubricant – a job it does very well – but it was originally designed to penetrate and remove dirt and corrosion. “WD” actually stands for “water displacement.”