The last two times ive ground my rim, its been wank when Im trying to say hold it on the backwheel on a slope going up. To describe it another way, If i were to manual and about to loop out, if I brake it WILL grab me really well. But if I was lowering my bike from backwheel position or "fakieing" the bike back between my legs it would barely hold at all. Grind seems quite beasty pads are square to the rim, cant think of anything else. Any ideas anyone?