Truggy tires

I just converted a Losi Muggy. I don't know if you'd actually call it a Truggy, but I'm going to be racing it in truggy class. Anyway, as I said, this is my first truggy and I don't know anything about setting them up with tires.

What do you guys recommend? What I need to know is what is the difference among the different sizes and such. It has 420s on it now and they are really big. From what I've seen, truggies typically run something just a bit wider and taller than buggy tires. What are 40 series tires?

Any info would be appreciated.

Thanks.