Investors might want to bet on Sonic Automotive (SAH), as earnings estimates for this company have been showing solid improvement lately. The stock has already gained solid short-term price momentum, and this trend might continue with its still improving earnings outlook.The rising trend in estimate revisions, which is a result of growing analyst optimism on the earnings prospects of this auto dealer, should get reflected in its stock price. After all, empirical research shows a strong correlation between trends in earnings estimate revisions and near-term stock price movements. This insight is at the core of our stock rating tool -- the Zacks Rank.The five-grade Zacks Rank system, which ranges from a Zacks Rank #1 (Strong Buy) to a Zacks Rank #5 (Strong Sell), has an impressive externally-audited track record of outperformance, with Zacks #1 Ranked stocks generating an average annual return of +25% since 2008.For Sonic Automotive, strong agreement among the covering analysts in revising earnings estimates upward has resulted in meaningful improvement in consensus estimates for the next quarter and full year.The chart below shows the evolution of forward 12-month Zacks Consensus EPS estimate:12 Month EPSCurrent-Quarter Estimate RevisionsThe earnings estimate of $0.80 per share for the current quarter represents a change of +5.26% from the number reported a year ago.The Zacks Consensus Estimate for Sonic Automotive has increased 12.15% over the last 30 days, as three estimates have gone higher compared to no negative revisions.Current-Year Estimate RevisionsFor the full year, the company is expected to earn $2.46 per share, representing a year-over-year change of +38.98%.In terms of estimate revisions, the trend for the current year also appears quite encouraging for Sonic Automotive. Over the past month, four estimates have moved higher compared to no negative revisions, helping the consensus estimate increase 5.21%.Favorable Zacks RankThanks to promising estimate revisions, Sonic Automotive currently carries a Zacks Rank #1 (Strong Buy). The Zacks Rank is a tried-and-tested rating tool that helps investors effectively harness the power of earnings estimate revisions and make the right investment decision. You can see the complete list of today's Zacks #1 Rank (Strong Buy) stocks here.Our research shows that stocks with Zacks Rank #1 (Strong Buy) and 2 (Buy) significantly outperform the S&P 500.Bottom LineWhile strong estimate revisions for Sonic Automotive have attracted decent investments and pushed the stock 15.5% higher over the past four weeks, further upside may still be left in the stock. So, you may consider adding it to your portfolio right away.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Sonic Automotive, Inc. (SAH): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research