[_paralyzed_]

you definately do not want locked diffs. It will snap your axles and make it turn like a bus.(your inside wheels need to turn rotate slower than the outside in a turn.) The only tires I know of for monster trucks are pro-lines road rages, IMO they suck though. Maybe 17mm adapters and buggy wheels? We can't determine spur/pinion until we know what motor you'll use, what batteries you'll use, and how fast you want to go. Good Luck, and welcome to the forums!