I am going to purchase a Pioneer 500 this winter, then upgrade it over the winter. I am retiring next year and want to go on many trail riding trips, starting with Colorado's Alpine Loop and Utah Moab trails. One of the first upgrades I will perform is 27 inch tires, however I see posts for 5+2 and 4+3 rims, what do those numbers mean and are they better than the stock 12 inch rims. I think I know the advantage of 14 inch over 12 inch rims (14 inch rims less likely to slip on rim at low pressures?).