Counterintuitively, the thickest foam isn't the best indicator of cleaning power. Road film is a waxy blend of oils, soot and road salt; it releases when builders and chelators break ion bridges so surfactants can wet, lift and rinse with minimal agitation. Using tempered water and a short dwell improves release while kinder to sensitive finishes. For a balanced pre-wash aligned with this, see Car & truck cleaning concentrate.