The answer may surprise you.
It's surprising to see how long it took BMW to build M versions of its popular X3 and X4 SUVs. People love M cars and people love SUVs, so the X3 M and X4 M are just the products BMW needs to be building right now. Since BMW will likely never build the M3 wagon of our dreams, the X3 M and X4 M are the most practical alternatives to the M3 sedan and M4 coupe/convertible. BMW even says it designed the two SUVs with the goal of feeling as close to the upcoming M3 as possible. The company is so proud of its latest creations that a representative even told Motoring that the X3 M is forecasted to be the best-selling M car in the lineup.
"We expect the X3 M to be the highest selling M car,” BMW Australia spokesman Adam Davis said. Referring to the X3 M40i, Davis added, "It is now by far the biggest selling M or M Performance car in Australia, so it’s a logical progression for the X3 M to follow the same course for M cars.” 60% of all BMW sales in Australia are SUVs, so it seems valid to expect the X3 M to sell in high volumes. And since the X4 M is more expensive and sits in a more niche category, its sales won't be as high.
The current best-selling M car in Australia is the M2 Competition followed by the M3 sedan, M5 sedan, and M4 coupe. Interestingly, 85% of customers opt for a Competition model. Global BMW boss Markus Flasch says global sales should closely reflect the numbers out of Australia. "The X3 M will be within the high-performance segment, probably the highest selling,” he said. It seems crazy to think the best-selling performance car from BMW will also be an SUV, but that's just where the market sits right now.