Elon Musk's Tesla Inc. TSLA has postponed the U.S. debut of an affordable version of its Model Y SUV. The vehicle, internally known as E41, was initially set to launch in the first half of the year.

Leading up to the Model 3 launch, Tesla CEO Elon Musk boasted that Model 3 production would reach 20,000 units per month by the end of December 2017. An ambitious goal to say the least ...