I just bought myself a devinci district street/dirt jump bike. It comes with kenda k-rad tires. They are awesome in the city and on hardpacked dirt, but where I live I have some dirt roads I'd like to ride and plan to build some jumps in the woods, and as soon as the terrain turns a bit loose, you can say goodbye to any grip. I'm now looking to buy new tires that will have some grip in the loose stuff, without compromising too much on the street riding. What are your suggestions ?