Detroit automakers are quickly approaching their second-quarter conference calls on July 25, and for investors it can be difficult to keep track of key data throughout the three-month period leading up to earnings. Let's take a look in the rearview mirror at the important data and what it means for General Motors (NYSE:GM), Ford Motor Company (NYSE:F), and Fiat Chrysler Automobiles (NYSE:FCAU), and what else investors can expect to hear from management.

Q2 review

Let's compare key U.S. metrics for all three automakers, starting from the top with total second-quarter sales. FCA logged the largest sales gain at 7.9%, ahead of GM's 4.6% gain and well ahead of Ford's 0.9% decline. For investors, though, it's more important to understand what's actually driving total sales figures, because SUV and truck sales are far more profitable than car sales, and when you drill down to that level of data, the story is a bit different. 

GM's pickup sales, which includes both full-size and mid-size trucks, jumped an impressive 21.2% year over year during the second quarter. That result dwarfs GM's first-quarter year-over-year gain of only 2.4%. Meanwhile, Ford's second-quarter pickup sales moved 5.5% higher, and FCA's declined by 1.3%. Those figures suggest that GM and Ford had a better second quarter, with more profitable truck sales than the total sales gain would indicate. To put in perspective why that's important, consider that Morgan Stanley analyst Adam Jonas calculated in a March 14, 2018, note to investors that a 5% change in F-150 production could be worth roughly 10% to Ford's earnings. It can't be understated how much that sales of these highly profitable trucks can move the earnings needle.

Ford F-150 towing a boat on a highway.

Image source: Ford Motor Company.

Two more metrics investors need to consider are average transaction prices (ATPs) and incentive spending. As competition heats up and the U.S. new-vehicle market plateaus, incentives have been on the rise -- partially offset by increasing average transaction prices. During the second quarter, GM's ATPs moved 3.7% higher to $40,569, according to Edmunds.com, but its average incentive spending increased 8.1% to $4,125. Ford's ATPs moved a similar 4.1% higher to $40,221, with incentives rising a staggering 22.7% to $5,088. FCA trailed both with a modest 1.2% ATP gain, for a total of $37,360, and recorded a 13.2% incentive spending increase to $4,767. Investors will want to keep an eye on incentives, because if they get out of hand, it could quickly erode profit margins.

In summary, GM clearly appears to have recorded the strongest second quarter, with pickup trucks driving sales higher, all while posting the highest ATPs and lowest incentives among the Detroit automakers.

What else?

In addition to typical earnings data, investors can expect management to devote extra time on the call to the implications of President Trump's tariffs. All Detroit automakers are on the same page and have been hinting at the potential pain that would be caused by increasing tariffs. In fact, the Alliance of Automobile Manufacturers, a group representing major automakers, released a statement saying that 25% tariffs on imported cars and parts would increase the price of U.S. vehicles by $83 billion annually and cost hundreds of thousands of jobs. Ford has already warned investors that the rise in aluminum and steel costs would dent 2018 profits, and any further tariff war would exacerbate the problem. Expect automakers to take time to address this; additional tariffs are probably the biggest threat to auto sales and profits.

Jeremy Acevedo, Edmunds manager of Industry Analysis, said in an emailed press release:

A strong economy gave auto sales a solid boost in the first half of the year, but in many ways the industry is operating on borrowed time. Shoppers are getting stretched thinner and thinner, as interest rates and vehicle prices continue to rise. While these factors alone could drive a market contraction, tariffs have the ability to cause a dramatic snap back. If tariffs cause a significant economic slowdown in tandem with spiking vehicle prices, the impact on the auto sector could be devastating.

Expect a solid quarter

All in all, as investors tune in Wednesday for automakers' conference calls, the reports should all be pretty strong, with sales of highly profitable vehicles thriving. It would appear that GM put together the most well-rounded second quarter, with sales of trucks soaring and incentives remaining in check. Investors should also anticipate a serious and gloomy tone alongside solid earnings, because the impact a tariff war could create is a very real threat to automakers' bottom lines.

Daniel Miller owns shares of Ford and General Motors. The Motley Fool recommends Ford. The Motley Fool has a disclosure policy.