Data: AAA; Chart: Axios VisualsThe price of diesel fuel has surged above $5 a gallon in the U.S., the highest in four years, creating new inflationary pressure on anything Americans buy that relies on truck transport — which is to say, pretty much everything.Driving the news: The average retail price of a gallon of diesel was $5.04 Tuesday, AAA says, up from $3.65 a month ago.That amounts to a 38% one-month rise in the price of diesel, surpassing even the 30% rise in the price of regular unleaded gasoline over that span. The Iran war has choked off supplies of crude oil and other commodities from the Persian Gulf, driving up global prices.State of play: Most Americans have little direct exposure to diesel prices; gasoline-fueled (and, increasingly, electric or hybrid) cars are the norm.Many houses, especially in the Northeast, rely on heating oil, a close chemical cousin of diesel. Thankfully, spring is arriving.The indirect effects of higher diesel prices, however, are enormous, flowing through to essentially all goods, at a time when supply chains are already stressed by higher tariffs.Tractor-trailers, trains and many ships rely on the fuel, so the price of bringing virtually all goods to market has risen markedly in the space of a few weeks.Between the lines: That isn't likely to result in immediate price increases, but will shape the pricing decisions companies make in the weeks ahead — especially for heavy, bulky and inexpensive goods for which transportation is a large share of their total cost.That means that higher diesel prices could thus drive core inflation measures higher, not just the headline measures that include the direct cost of higher energy.The Federal Reserve will have a harder time looking through those price hikes if they show up in core goods, as opposed to just in retail gasoline or electricity prices.