It really depends on what you're trying to accomplish. If you're working on a vehicle that is extremely contaminated with brake dust and other contaminates, I would use wheel soap, dish soap or a mild cleaner as a lubricant with a small portion of a clay bar. Not many places sell "wheel soap", usually it is an all around vehicle soap which may be "good" for the paint, but not necessarily for the wheels, and vice versa. I say dish soap because the chemicals are generally too harsh for paint but may be safe for wheels. I used Simple Green on my 95 ZJ when i bought it, but diluted the spray bottle even more, and it actually did pretty good. But like others have mentioned, those kits come with 2 clay bars (usually) with the brands lubricant and a towel. So, personally, if i bought one of those kits, i would use one for just wheels.. but not a whole one, i would say half of one broken again into 1/4 pieces for each wheel. But be sure to get as much dirt off the wheel as possible before using clay, also, work outside of the wheel in.