I just received my new Rad Mini 4 this week. I intend to use it mostly for maintaining my horse trails in the woods, and the local roads are gravel. It came with very smooth road tread tires, CST Big Boat tires that don't provide any traction on dirt trails. On Rad's website it looks like the most aggressive tires are Kenda Krusade 20" x 4", and they are out of stock. does anyone know of other tires available that are as, or more, aggressive that are available elsewhere?