Pros And Cons Of 10" Rim

Bought 21 X 12 X 8 7 paddle haulers on 8 X 8 rim, 68 rollout. When I put them on the bike, the just barely clear the heel guard, and I really don't like riding withoout one. I am assuming that these tires will GROW, when you put speed to them and I don't want to ruin a new pair of tires Spoke with Joe at Fullertons (great guy again and as always), and he is sending me another set of tires but on 8 X 10 rims. So my question is, what will be the difference, both good and bad between these tires on these two different rims. <_<