Here is a cool little graph that shows you the mathmatical equation to find out your final drive and crawl ratio.
http://www.offroaders.com/tech/mph-crawl-ratio.htm
You will end up with an answer like 58:1. The higher the left number, the higher your RPMS will be at a lower speed and the purpose being that you are transferring maximum torque and HP to the wheels and ground at low low speeds.