http://www.investorglossary.com/kicking-the-tires.htm
http://dictionary.reference.com/browse/kicking the tires

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Note added at 20 mins (2009-05-23 13:57:00 GMT)
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Kicking the Tires is a slang term referring to the research an investor will perform before making an investment. Kicking the Tires typically involves grassroots research such as calling and visiting the company at hand. Kicking the Tires can also involve questioning a financial broker or advisor about the company and engaging in other similar investigative research before investing in a stock. Kicking the Tires is not meant to be used as a sure-fire way to predict the outcome of a potential investment; rather Kicking the Tires is a method to help an investor stay informed and make as educated of a decision as possible. The term "Kicking the Tires" originated from consumers' tendency to start kicking the tires of an automobile, in scrutiny, as the salesman makes the pitch. Though it is not a certain predictor of a stock's performance, Kicking the Tires is generally recommended to help investors learn as much as possible about a stock.