10j steel wheel rims


Just took possesion of 4 new rims 15"X10j. Does anyone have any experience of this size rim on an idependant and what size tyres can be fiited. I had a quick look on www.bronco4X4.com and they state a 33.12.5 tyre. I fancy having some grizzly claws at this size or maybe slightly smaller if necesary/possible but not sure if they will fit without any mods etc and how this will affect gear ratios and economy etc? Any advise is very much welcomed.
Thanks in advance, Nige.