We can all agree that the X5 4.6is is a celebrated model.

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BMW's first performance SUV. The first worthy competitor to the ML55 AMG. Arguably the most thundering exhaust note of a performance SUV.

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But there's a design detail that's much subtler, but pioneering in it's own right. The enclosure of the exhaust tips within the bumper cover, instead of being below them. A design trait that would show up in many later models. Let's take a look.

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In the X5, there is a valence with the subtlest hint of a splitter under the exhausts. On regular X5' the exhausts were still enclosed, but the valence was smaller and the same black plastic as the whole lower-body. But on the 4.6is? Painted in the body color, you immediately knew that this thing meant business. Coupled with those fat rear tires, you had one of the squattest stances this side of Shaquille O'Neal.

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The ML55 went the route of more pronounced holes in the bumper for the dual exhaust, but nothing was below the tips. At the time it still looked plenty racy, however.

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Now you might be thinking "so what?" to such a seemingly small detail. But it visually connected the car to supercars before it.

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The F40 and F50 both had valences enclosing the exhaust exit. Quite the high performance lineage, to say the least.

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The benefits of such a setup make lots of sense for supercars. You protect the expensive exhaust components from road debris. You have space for a splitter below to improve rear aerodynamics, reducing rear turbulence and connecting to the belly pan. And you can presumably place heat shields between the valence and the exhaust, to keep that lovely paint fire-free.

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At the same time, it comes at the cost of more complicated serviceability. The tips also have to be placed higher, which adds interesting packaging dynamics; with the engine on the F40/F50 and the load floor of the X5.

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Clearly some of their countrymen were impressed, and Porsche implemented their own version with the Cayenne facelift in 2008. All models got enclosed tips, from the glacially slow V6 to the glorious Turbo S.

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Porsche would temporarily ditch them with the 958 pre-facelift, but came to their senses and brought them back for the 958.2 update in 2015.

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BMW made the odd decision to continue them with the subsequent E70 version in 2007, though these were reserved for all models below the X5 M.

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It just looks so purposeful. Even when afflicted with the frustratingly prevalent black plastic lower bodies of the majority of German SUVs in the first two decades of this century. Aston even jumped into the fray with it's own first SUV, the DBX.

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Now, I'm cherrypicking designs and obviously recognize that there were many performance SUVs that didn't enclose their exhausts. The Urus is a particularly strange choice given the permanent supercar flavor of any of its vehicles. But I chalk that up to its Audi bones and cost-cutting more than anything. But this trend started all the way back with the 4.6is, and it's still going strong a full two decades later.

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Designers are realizing that it's an effective method of reducing the mass of an SUV rear, while giving it a planted stance and keeping the pretty tips away from all of the mud and rocks in the Starbucks parking lot.

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So thank you, Frank Stephenson (lead designer of the original X5). You sure nailed it with the execution of a design that still looks great today. It must feel nice to continue to be copied!

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