Abstract: The invention is a replacement wheel/tire assembly for a vehicle where the new assembly maximizes the balance between travel efficiency or mileage of the vehicle and traction requirements of the vehicle tires for safety and/or high performance. The invention yields an efficient driving mode on large diameter tires and a performance driving mode on small diameter tires, with passive and automatic transfer between these modes. Multi-diameter tire and wheel assembly comprises: at least one large diameter tire, at least one large diameter wheel, at least one small diameter tire, at least one small diameter wheel, and a wheel connection means. The number of wheels is equal to the number of tires in each multi-diameter tire and wheel assembly. Each large diameter tire is mounted and inflated onto one large diameter wheel and each small diameter tire is mounted and inflated onto one said small diameter wheel.