between the two  revenuer cars. The front fenders were made of cast steel and the  body and frame were heavily reinforced. The weight of the car was  such that special solid sponge rubber tires had to be fabricated and  used. No tire of the day could support the weight and speed the car  had to attain and still look like normal car tires. The engine also  had to be highly modified to produce the horsepower necessary for  the speed requirement.