Ford's F-150 has an uphill battle to gain on Chrysler's hot Ram 1500. Photo credit: Ford Motor Company.

How will Ford (F 0.48%) fight back against the Ram?

Fiat Chrysler's (NASDAQOTH: FIATY) Ram pickups have been selling like hotcakes -- up 23% so far this year. Meanwhile, Ford's F-Series line is up less than 4%.

Ford says that its share of the pickup market was unchanged in the first quarter of 2014 versus last year. But it slipped a bit in April. 

That won't do for the Blue Oval. The F-Series is Ford's most important product, and its most profitable one.

What's going on, and how can Ford respond?

Right now, the F-150 is Detroit's oldest truck
Ford has long been America's pickup-truck leader. That's still true, but the Ram has been on a tear recently. 

That tear got under way in earnest after the Ram 1500 got a significant overhaul for the 2013 model year. From the outside, it didn't look a lot different. But inside, there was a much-improved interior, and under the hood was a new eight-speed automatic transmission that significantly improved fuel economy. 

The 2014 Ram 1500 is a handsome truck, and a nice one to drive. Reviews have been very positive, and sales have been strong. Photo credit: Fiat Chrysler.

Suspension tweaks (plus that new interior) made the Ram a much nicer pickup to drive. Comparison-shoppers noticed, and critics have also noticed: The Ram was Motor Trend's Truck of the Year in 2013 and 2014, and it's currently Consumer Reports' top-rated pickup. 

Meanwhile, the F-150 hasn't changed much. Ford gives it some updates every year, but America's best-selling pickup hasn't had significant changes since 2011, when Ford replaced its engines with a line of more fuel-efficient options. The truck's basic design dates to the 2009 model year.

The F-150 and its Super Duty siblings are still very competitive products, though. In fact, given the Ram's recent overhaul, and the all-new Chevy Silverado and GMC Sierra that General Motors (GM -0.50%) introduced last year, Ford has done well to (mostly) keep pace.

But there's more to the story than that.

It's not just about the trucks themselves
You may recall that March's U.S. auto-sales numbers came with a surprise: For the first time in almost 15 years, the Ram 1500 outsold the Chevrolet Silverado.

That got people's attention all throughout the auto business. What had Fiat Chrysler done to make the Ram so strong? And what was GM doing wrong with its all-new trucks?

The answer to both of those questions turned out to be incentives. Chrysler was giving fat discounts averaging more than $5,500 per truck -- 46% higher than GM's, according to J.D. Power. 

Incentives are a big part of the pickup business. While discounts are only part of the picture for individual consumers, they're a very big deal for commercial-fleet buyers. Lately, those kinds of buyers -- think homebuilders and oilfield-services companies, among others -- have been buying an awful lot of pickups. 

That means incentives can move the market in a big way. (It also means that they're a cost of doing business in the full-size pickup realm. Why are Detroit's average incentives higher than the foreign competition's? This is why.)

Being stingy with pickup incentives was very good for GM's first-quarter profits. But it wasn't so good for GM's pickup sales, particularly at the low end of the market -- where the Ram was able to gain ground.

But things returned to normal in April: The Silverado outsold the Ram by 6,081 vehicles last month. The Ram still did well -- sales were up 17% -- but GM came a lot closer to keeping pace. Sales of the Silverado and the GMC Sierra were up a combined 12%.

Why did things change?

GM boosted its offers in April in what it said was a targeted way. It gave lower-end double-cab and V6-powered models extra discounts in an effort to win back lost ground from Ram. GM's discounts rose to around $4,400 a truck, according to J.D. Power figures provided to The Motley Fool. 

Meanwhile, Chrysler dialed their incentives back to something closer to the industry average -- around $4,200 per truck, per J.D. Power. Ram sales were still strong, but GM's got better -- and both beat Ford's modest gain, because they beat Ford's incentives.

How Ford will fight back against the Ram's gains
Ford has held its incentives relatively steady for months, at an average around $4,000 per truck.  That varies a bit from month to month, as Ford makes regional adjustments -- and as the "mix" of pickup models varies. (Different models get different discounts.)

Ford's incentives were around $3,700 per truck in April. That was down about $210 from its March average -- and it was probably down a little too far.

So what will Ford do in May? I don't know for sure, but I can make an educated guess, and I bet you can too: Expect Ford's discounts to rise -- but in a careful, moderate way.

Ford's incentives in May 2013 were higher than they have been recently, around $4,300 per truck. That gives Ford some leeway: It could boost its discounts from last month's levels quite a bit, making it more competitive with offers from Chrysler and GM, while still being able to say that its per-truck spending on incentives had fallen year over year.

A boost in sales that came without exceeding last year's incentive levels would reassure Ford's investors, who worry about the impact of incentives on Ford's profit margins -- and about lagging pickup sales.

It seems like the obvious move. Will Ford make it? Stay tuned.