This month I've got dirt on my mind again, because that's usually the result of a four-wheeling excursion. There are other terrains that provide alternatives such as sand or rocks, but they can be harder to find here in New Zealand.
A problem with dirt is that it's often in the form of mud and that stuff is not popular with a large proportion of the general population. There are probably a lot of four-wheelers who've regretted the effect of mud on the mechanicals of their