Cape Town - So, any petrolhead worth his, uhm, oil, will be aware of BMW’s bespoke xDrive all-wheel drive system - nowadays available on virtually all model configurations in the Munich-based carmaker’s range.
What’s probably not so widely known is the role of the German marque, which celebrates its centenary this year, in popularizing the letter X to signify all-wheel drive three decades ago.
Originally, the X symbol in the car industry (as in the aircraft industry) was primarily used to indicate experimental vehicles, but over the years this has changed to include four-wheel drive models, and more recently, crossovers.
Strictly speaking, the letter H is a more appropriate letter to indicate all-wheel drive, but for some reason it never found favour, with X now universally accepted in this regard.
40 years ago
The origins of X go back 40 years, to 1986, when BMW introduced the E30 325iX after unveiling its 325i “Allrad” at the 1985 Frankfurt Motor Show.
The original X had a 4WD system consisting of a planetary centre differential with a permanent 38:62 (front-back) torque split. Both the centre and rear differential had a viscous lock which engaged automatically when slippage occurred, but the front diff had no lock of any kind.
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The model, built until 1991, was available in sedan and touring station wagon form (from 1988) and it could be distinguished from normal derivatives by quite noticeable fender flares.BMW 325ix (E30). Image: BMW Group
From 1991 the system was also used in the E34 5-Series - initially the 525iX model (with a 36:64 torque split) had a separate control unit for the electromagnetic semi-wet multi-plate centre clutch and the electrohydraulic wet rear diff, which received wheel sensor data from a special, modified ABS unit.
From September 1993 the second generation system on the X-model incorporated an ABS/ASC+T unit which controlled the semi-wet electromagnetic multi-plate centre clutch through throttle control and an automatic brake distribution (ABD) system. While it was built until 1996, only 9366 units of the E34 525iX were produced.
The one good thing that came out of the BMW merger with Rover in 1994 was the acquisition of Land Rover four-wheel drive technology. This helped Munich to develop its own SUV - the X5 Sports Activity Vehicle (SAV) - that was unveiled in 1999.
As its sedan predecessors, the X5 used a planetary gear system to split the power 38-62% in favour of the rear wheels, but also added systems such as ADB-X (Automatic Differential Brake) electronic traction control, DSC (Dynamic Stability Control) and Hill Descent Control (HDC).
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In 2001, after a ten year hiatus, this system was also made available in the facelifted E46 3-Series. Now designated xDrive, it was available for the six-cylinder 325xi and 330xi sedan and wagon (touring) models.
These 3-Series models were also built in Rosslyn (Pretoria), but only for export, and were never made available locally. Later, xDrive was also supplied for the BMW 3-Series Coupe.
A completely re-engineered xDrive system arrived in 2003, debuting in the X3 and soon after - in 2006 - in the revamped X5 with Integrated Chassis Management system (ICM).
This system could send 100% of the power to the front or rear axle, using DSC data such as accelerator position, steering angle and lateral acceleration to continuously adjust the power split.
In 2007 the X6 Sports Activity Coupe (SAC) made its debut at the Frankfurt Motor Show (IAA) with xDrive as standard. At the same time Dynamic Performance Control (DPC) marks its debut in the premium segment.
Two years later, in 2009, xDrive is introduced into the luxurious BMW 7-Series, while in 2010 the BMW ActiveHybrid X6 for the first time combined all-wheel drive with a hybrid powertrain.
xDrive was also then made available in the M derivatives of the X-range, while the first two all-wheel-drive models in the 6-Series, the Coupe and Convertible, followed in 2012.
READ: Escape the everyday in the BMW X1Family X: The current crop of BMW X-cars. Image: BMW Group
In 2013 the 4-Series Coupe with xDrive followed, and the next year the 2-Series Active Tourer combined xDrive with an all-new front-wheel-drive setup.
In 2014 the BMW i8, equipped with a special form of all-wheel drive that pairs a plug-in hybrid drive system with an internal combustion engine driving the rear wheels and electric motor driving the front wheels, was introduced. Last year, in 2015, the plug-in-hybrid BMW X5 xDrive40e combined xDrive with eDrive, and the 225xe, which combines plug-in hybrid drive with front-wheel drive platform made their debut.
BMW now offers more than 110 models with xDrive, and more than five million all-wheel drive derivatives have been sold worldwide - accounting for more than a third of all new BMW registrations.
Why, it has even been officially confirmed that an xDrive variant of the mighty BMW M5, and perchance an M6, will be made available (presumably by 2018) after the unveiling of the new G30 5-Series.
Oh, and should there be a BMW “bakkie” in the near future, be sure it will feature xDrive as well.
Fact is, with BMW popularising the X symbol rival manufacturers (such as Lexus) also started using it to differentiate their all-wheel drive models, and others like Fiat, Mazda and Hyundai, uses it to discern crossovers from their normal offerings.
However, it’s clear that BMW’s direct competitors - Mercedes (with the G-Class) and Audi (with its Q-series) - are ignoring X as much as possible.