the tire failure expert relied on features of tire technology that the manufacturer did not dispute, as well as background facts about the particular tire on the carmichaels' van. the expert's conclusion that a defect in the tire caused the accident rested on certain observations about the tire that kumho tire vigorously disputed. kumho also disagreed with certain aspects of the tire expert's methodology, and asked the federal district court hearing the case to exclude it under rule 702 of the federal rules of evidence.