Heavier surface contaminates (bituminous asphalt (tar), traffic film, etc) can build up on the paint surface over time, which will require a stronger solvent than just soap and water; you may want to utilize a safe degreaser. Wurth Citrus Degreaser is a multi-purpose, citrus base, concentrated degreaser that emulsifies grease and oil without harsh acids or alkalis, 100% biodegradable formula out performs hazardous solvent degreasers, which can be diluted with distilled water to the desired strength, to break up and loosen dirt, tar, sap, bird droppings, and other stubborn forms of surface contamination.
It's should be carried out prior to washing your vehicle, this will ensure that all residue and the degreaser is washed and rinsed away. It's important to note that degreasers will usually remove surface protective layers of sealant or wax, so it’s important that you re-apply your paint protection product(s)