Rivian Automotive (RIVN -2.90%) investors have been very happy over the past month. The valuation of this electric car stock has surged by roughly 40%. Looking under the hood, however, it's easy to project significantly more growth to come. There are three major reasons investors should consider buying Rivian shares before the company's next earnings call, which is expected to occur sometime around Aug. 5. 1. Rivian's growth rates are about to explodeRivian has been experiencing a period of sluggish sales g ...