Ferrari was still using wire wheels as late as 1965. Cobra's were pretty light cars (2,300 pounds) but the combination of the increased torque of the race prep 289 engine and the wider and grippier Goodyear tires that Shelby began to use was too much for the wire wheels that were attached to an obsolete suspension system. Mag wheels proved to be stronger and cheaper than upgrading to stronger wire wheels from a manufacturer like Borrani.