New X4 M40d performance model will please not just torque junkies, but those who want a focused, enjoyable, and very BMW driving experience
Photos: BMW, Derryn Wong
BMW Performance Centre
Spartanburg, SC, USA
The X3 and X4 operate as a complimentary pair, but it’s interesting that the X4 has now debuted two important somethings before its odd-numbered brother: A new M40d variant, and the new M Sport differential (see box).

The M40d diesel high-performance variant that packs a 3.0-litre turbodiesel with 236hp. Not a whole lot, compared to the 360hp from the M40i model, but it does have 680Nm of torque on hand.

There will be an X4 M40i, but it isn’t in production yet, and there were none on hand to test, but it will eventually be Singapore-bound.
What we did test was the new M40d on the BMW handling track and wet skidpan, and we won’t be getting it back home, but it provides a good analogue of how the X4 M40i might behave: Despite the power deficit, the X4 M40d hits 0-100km/h just 0.1 second slower than the X3 M40i does.

BMW Performance Centre’s handling track is a driver’s joy. It’s not particularly wide, and with no runoff. Adding to that are the dramatic elevation changes with both up- and downhill blind turns.
 
In short, it requires lots of confidence and commitment from a driver – or a particularly agile and supportive car, which to our pleasant surprise, the X4 M40d seems to be.

The car we drove, with adaptive suspension, exhibited excellent body control, meaning screaming through blind downhill bends was less intimidating than it otherwise would be.

Larger brake discs/master cylinder provided good stopping power, with linear feel, all very useful considering how quickly the M40d gains momentum, and perfect for setting up entry into slower corners.
In fact it came as a bit of a surprise to find out the car weighs nearly two tonnes (1,895kg without a driver), as it masks its weight superbly on track.

That the inline six diesel engine sounds properly throaty and exciting is a great bonus, and a fitting cap to a gutsy driving experience.

Like the best example of its predecessors, the X6 M50d, the X4 M40d feels more like a hot hatch wrung large, rather than an roly-poly SUV dressed up and thrust unwillingly into track duty.

That’s how we would describe a typical coupe-like SUV at this level in this sort of situation, but it seems the X4 M40d runs very much against type.

BMW X4 M40d

 
 
 

Different strokes: What BMW’s done to make the X4 handle like a real BMW coupe


Besides the steering and suspension differences (see main story), the X4 M40d also packs a new M Sport Differential. A single-clutch electromechanical rear differential, it emulates the behaviour of a limited-slip differential.
Unlike the system found on the X6 M and X6 M50d, it’s not a torque vectoring system, so it doesn’t actively send power to the outside wheel, but rather concentrates on improving handling by managing the locking of the inside wheel.

Steffen Koch, the manager in charge of driving dynamics for the X4, says that besides minimising understeer on the corner exit, and oversteer on corner entry,  endows the X4 M40d with behaviour that’s closer toward that of a rear-wheel drive vehicle, in addition to the xDrive system’s default 20/80 front-rear torque split.

The differential also modifies its behaviour depending on the DSC mode (as opposed to drive mode), with it locking more readily in DSC sport (or as BMW calls it ‘Traction’ mode), and even more with DSC off.
This we found out with repeated runs on the wet skidpan, with the car able to generate serious cornering force, despite the slippery surface with less than uniform grip in each section. Tightening up the cornering line was a simple matter of gently lifting the throttle. With traction mode, it was even more fun, the car allowing its wheels to slip more, and with DSC off, we could also provoke the car into easily controllable lift-off oversteer.