I can't imagine why anyone would want to make their car totally loose rather than increase traction. If everyone is using yellows why would you want blacks, to hit every wall, tube and car on the track and make a bunch of enemies?
Get out there and use those chunked tires for practice then maybe in time you'll get more than one race per set. Haven't you noticed that even the skilled drivers chunk a tire every now and then.
Someone mentioned F1 tires. You may be able to modify them to work on a 1/12. It would cost you a bit but the tires would last longer.