Ford's pickup sales gains have lagged rivals' while its dealers wait for the all-new 2015 F-150 to arrive. Source: Ford Motor Company.

Analysts are forecasting more lost ground for Ford Motor Company (NYSE:F) as the month comes to a close. Automakers will report their monthly U.S. sales results on Wednesday, and forecasts call for another tough month for Ford.

Edmunds predicts that Ford's sales will fall 3.9% on a year-over-year basis -- and that Ford will be the only major automaker to post a sales decline for September.

Edmunds also predicts that overall U.S. auto sales will be up 11% in September -- and that General Motors (NYSE:GM) and Fiat Chrysler (OTC:FIATY) will post market-beating gains. 

What's the deal?

Strategic moves have held back Ford's sales gains
Ford continues to lag rivals' sales gains because of a couple of strategic decisions made (for good reasons) by Ford's management. 

First, for the past several months, Ford has made year-over-year reductions in the total number of vehicles it sells to rental-car fleets. Those sales generate lower profits than retail sales, and with several of Ford's factories running at or near maximum capacity, the company wants to allocate its supplies to the channels that will generate the most profit.

Second, Ford expects supplies of its F-150 pickups to tighten by year-end. The complicated factory changeovers needed to produce the all-new aluminum-bodied 2015 F-150 have required weeks of downtime at Ford's two truck plants. Ford North America chief Joe Hinrichs estimates that the company will have lost 90,000 units of production by the time the changeovers are completed.

Those supply concerns led Ford to cut its truck incentives earlier this year. That helped Ford's profits remain strong last quarter. But F-Series sales have suffered, and the company has lost market share as GM and Chrysler have jumped on the opportunity.

Chrysler's streak of big sales gains looks set to continue
Edmunds predicts that Chrysler's U.S. sales will rise 15.4% in September.  Analysts at TrueCar expect a slightly higher gain, 17.5%, and estimate that Chrysler's incentives will come in at an average of $3,644 per vehicle for the month. That's down 5.2% from last month, but a significant increase over what Chrysler was spending a year ago.

Chrysler isn't the only automaker spending more on incentives than it did a year ago. Nearly all of its rivals have followed suit. TrueCar's experts attribute the across-the-board rise to an increase in average transaction prices, as buyers across the industry are taking advantage of cheap financing to opt for more expensive and better-equipped new vehicles. 

Chrysler's Ram 1500 has won many accolades from reviewers, while Chrysler has won over price-sensitive buyers with generous incentives. Source: Fiat Chrysler.

TrueCar president John Krafcik doesn't think that's a problem. Krafcik said in a press release last week that "incentive spending and transaction price growth are at healthy levels" and he expects "another strong month for the industry" in September.

But Chrysler's per-vehicle spending on incentives leads the industry, and that's in part a reflection of the company's aggressive efforts to gain market share in full-size pickups. Through August, sales of Chrysler's Ram pickups are up 21% this year -- and the company likely made further gains in September.

There's a downside to that big spending, though, and it shows up on Chrysler's bottom line. The Chrysler Group's operating profit margin was just 4.8% in the second quarter, miles behind Ford's 11.6% margin in North America over the same period. 

Fiat Chrysler CEO Sergio Marchionne has promised to rein in Chrysler's incentives in coming months, hoping to boost that profit margin. 

But meanwhile, GM is making its own move to take advantage of Ford's supply issues.

After several sluggish months, a big jump may be in the works for GM
Edmunds estimates that GM's U.S. sales will rise 22.2% in September. That would be a whopping increase for the General. Through August, GM's sales were up just 2%, as a major recall scandal and a conservative approach to incentives held back gains.

GM's recall scandal may not have completely faded into history's rearview mirror, but the company has loosened its purse strings when it comes to pickup incentives. TrueCar estimates that GM's incentive spending will average $3,336 per vehicle in September, comparable to Ford's, as GM seems to be moving aggressively to boost sales of its Chevy Silverado pickup.

Sales of the new-for-2014 Chevy Silverado have been just so-so, but the new trucks have made a greater contribution to GM's profits than their predecessors. Source: General Motors Co.

The Silverado was all-new for 2014, and it was generally praised by critics -- but sales gains have been lackluster, in part because of that conservative approach to incentive spending. Boosting profit margins is an ongoing priority for CEO Mary Barra, and GM's incentive discipline was expected to continue. 

But Automotive News is reporting that GM sharply boosted its incentives to Chevy dealers in September, offering generous bonuses to dealers that hit aggressive sales targets for the Silverado. I expect to see a big jump in GM's pickup sales when it reports its monthly sales totals on Wednesday.

The upshot: The pickup wars are in full swing
We focus on pickups because they're far and away the best-sellers -- in the U.S., at least -- at all three of the Detroit automakers. And they're a huge source of profits for each.

If these analysts' estimates hold -- and history has suggested that they capture the trends more often than not, even if the exact numbers differ -- then it looks like we're in for a major pickup battle as Ford gears up to launch its all-new trucks.

That could result in some great deals for consumers. But it'll yield further drama in the sales numbers -- and more important, some potential for movement on the bottom line of each of these companies. Stay tuned.