This week’s encouraging earnings reports from the big U.S. car makers are more than just positive signs for the North American auto industry. They could rev up the entire back-firing economy.

The better-than-expected financial results from General Motors Co., Ford Motor Co. and Chrysler parent Fiat SpA shared a common trait: surging sales in North America. The results dovetail nicely with the latest U.S. auto statistics for September, which show new-vehicle sales jumping nearly 3 per cent in the month to their highest level since 2008. The numbers mark a significant watershed: For the first time since the Great Recession, the size of the U.S. vehicle fleet didn’t shrink.