TCR-40 Rubber Tire Cast Question?

Has any one used this be for its not that good for tires "Fishing bate" yes but a little soft for tirs can any one tell me how I can make this stuff a little harder or can I use Quick-set RTV Silicone to make my tires. :banghead: :banghead: thanks
http://i162.photobucket.com/albums/t248/White_r34/Vincents%20How%20tos/TCR-40Rubbertirecast.jpg
http://i162.photobucket.com/albums/t248/White_r34/Vincents%20How%20tos/MakingTires3.jpg