In the sales battle between America's top two automakers, there has been a clear winner for the past year or so. General Motors (NYSE:GM) has bounced back strongly from the ignition switch recall scandal that emerged two years ago, gaining ground against top rival Ford Motor (NYSE:F).

This trend continued in January. While the overall sales growth numbers for GM and Ford didn't look that different, the underlying trends are far more favorable for the General.

GM has a strong start
In January, General Motors posted a 0.5% year over year gain in U.S. deliveries. This masked a strong performance on the retail side. Retail sales actually rose 8.9% year over year, but this was offset by a decline in daily rental sales.

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GM saw strong retail sales growth in the U.S. last month. Image source: The Motley Fool.

GM has been deliberately cutting back on sales to rental car companies in the past year or two. Not only do automakers earn low margins on most rental car sales, the result is a steady flow of used cars that will drive down residual values for those models. That in turn impacts retail sales by increasing leasing costs and reducing trade-in values.

General Motors cut back on sales to daily rental companies by nearly 13,000 vehicles last month. If GM had kept daily rental sales flat, it would have generated a roughly 7% increase in vehicle deliveries, rather than the 0.5% gain it reported.

Ford goes the other way
Ford reported a 2.6% decline in U.S. deliveries for January. However, while GM's January sales performance was hurt by its decision to cut back on daily rental sales, Ford actually sold more vehicles to rental car companies last month than it did a year earlier.

Ford stated that 14% of its January deliveries went to the relatively unprofitable daily rental market, compared to just 10% in January 2015. If Ford had held daily rental sales flat, it would have recorded a roughly 6% decline in deliveries last month.

From a business perspective, Ford's weak retail sales trend is aggravated by high inventory levels. Ford ended January with more than 100 days of supply in inventory, compared to just 74 days of supply at GM.

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Ford's car inventory is stacking up. Image source: The Motley Fool.

So far, Ford has held firm on pricing, but it may need to offer bigger discounts in the near future to clear out its car inventory, given how much demand has shifted toward crossovers and SUVs. Indeed, Ford ended January with 13% more car inventory than SUV inventory, even though its SUV sales outstripped its car sales by nearly 10% last month.

Ford needs new models
A big portion of Ford's weaker sales trend relative to General Motors can be explained by its absence from two key market segments.

First, Ford doesn't sell a subcompact crossover in the U.S. By contrast, GM has been a pioneer in this rapidly growing market segment with the Buick Encore and the Chevy Trax. Combined sales of these two models totaled 130,579 units last year. Furthermore, Encore sales rose 42% year over year last month, while Trax sales more than doubled.

Second, Ford doesn't sell a mid-size truck in the U.S. anymore. GM reintroduced its Chevy Colorado and GMC Canyon mid-size trucks in late 2014 and sold 114,507 of them last year. Given Ford's understandable desire to maximize pricing for the F-150, it can't really compete for highly price-sensitive truck buyers.

Ford already sells a subcompact crossover overseas: the EcoSport. It also sells the Ford Ranger mid-size truck in most of its overseas markets despite discontinuing it in the U.S. a few years ago.

Ford Ranger

Ford ended U.S. production of the Ranger in late 2011. Image source: Ford Motor Company.

Ford plans to bring both the EcoSport and the Ranger to the U.S. -- eventually. However, these models probably won't be available here until 2018 or 2019.

If recent demand trends continue, Ford's absence from the subcompact crossover and mid-size truck markets in the U.S. could hurt quite a bit in the next couple of years. The sooner it can get the EcoSport and Ranger ready for the U.S. market, the better off it will be.

Adam Levine-Weinberg owns shares of General Motors. The Motley Fool recommends Ford and General Motors. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.