Good God there is some bad information in here....

If you don't want to spend the money for a quality (Not over the counter) wheel cleaner, just use a more highly concentrated solution of car wash soap.

Clay bar will work better if it's slightly warm, but never do it in direct sunlight and ALWAYS use a high quality detail spray as a lubricant. And remember, clay is an abrasive. It can and most likely will cause some paint haze. I would only clay bar your car if you intend on doing an extensive detail on your car (Strip, polish, wax)