Step 16: New tires
As I mentioned before, I found the largest tires I could for the 8x8 rims. These were the blue knobby 11x22 tires you've seen in most of the pictures.
The problem is they were so square in profile that you had to lean 2 feet over the side of teh bike to steer at speed.
I ended up buying a used pair of tires/wheels. These are much rounder in profile and handle much better.