Another compromise has to do with the full-size spare tire, which goes missing in the Cayenne Diesel, displaced by the AdBlue reservoir (diesel models get a space-saver spare).
Also, to comply with prevailing U.S. emissions standards on nitrogen oxides, or NOx, these big diesels require fairly complicated systems of postcombustion treatment with a water-based urea solution, called AdBlue.
Topping off the Cayenne's 22-liter AdBlue reservoir is part of the regular service schedule, but it's entirely possible to run out of the stuff between services, depending on how you drive.