[RC-Monster Mike]

The gearing works the opposite with the spur gears. The more teeth on the spur, the lower the gearing (slower). Pros and cons are only a matter of finding the right combo for your track. Personally, I like the 66 tooth spur gear and locking the tranny in second gear. This way, I use a small spur and a small pinion and keep the weight as close to the center line as possible. Certain motors may require lower gearing, which would be a reason to use the bigger spur gear. Other than gearing selection, there really is no advantage/disadvantage to either size.