Firestone spokesman Phil Pacsi disagrees. He says tire-tread vibration is more violent and unlikely to be mistaken for any other problem. Only the Ranger compact pickup, from which Explorer is derived, has a similar cupping rate. Ford admits it can't fix the problem but insists it is not connected to tread separation. Tire-industry experts agree, noting that cupping occurs on the exterior of the tire, while tread separation is internal.
Cupping is a concave wear pattern, usually on the outer edges of the front tires.
It often is accompanied by vibration. Suspension problems would cause Explorers to handle unpredictably in emergencies. A number of cases involve Goodyear tires, suggesting that Explorer, not Firestone, is the cause. We have a technical team working to see that this comes up less frequently, or never.