A 135kW front-wheel drive electric car on steeply sloping wet cobblestones - a conventional traction control system would tie itself in knots. Picture: BMW

Munich, Germany - The defining performance characteristic of electric vehicles, whether on two or four wheels, is their instantaneous reaction to accelerator input.

An electric motor produces maximum torque just above zero revs, so even a moderately powered electric scooter will surprise drivers of conventional vehicles away from the lights.

But there’s also a flipside to that: conventional traction control systems, which rely on measuring the difference in rotational speed of the wheels and gently braking the wheel that’s turning too fast before the wheelspin gets out of hand, simply don’t react fast enough in marginal conditions such as adverse weather, accelerating hard out of slow corners or regenerative braking, which can really tie a four-channel TC set-up in knots.

BMW was faced with this problem during the development of the new, more powerful i3s, which combines peak output of 135kW with an instantaneously available 270Nm at 0 rpm - which, from a traction control point of view, is akin to dropping the clutch on a V8 muscle-car.

Higher demands

While this is not an issue on the i8 sports-car, which is intended to be driven by enthusiasts in good driving weather, it could have been a problem on a commuter hatch meant to be driven by Joe (or Josephine) Average all year round, in all weathers.

BMW head of chassis development Peter Langen explained: “Electric motors make significantly higher demands on driving stability systems than conventional power units, with their high levels of torque and instantaneous responses to every movement of the accelerator.

So his engineers developed a new type of system, geared squarely to the demands of electric mobility. Instead of gauging the spin factor remotely from the wheel hubs, it’s now calculated directly in the powertrain, short-circuiting the process and making it 50 times faster.

Then somebody pointed out that, because the ECU on  a modern clean-burning combustion engine has to accurately measure the crankshaft position in real time, that data could be used to drive the new, faster-reacting traction control system on conventional cars as well.

Thus, within the foreseeable future, the new traction control system will find its way into front, rear and all-wheel drive BMW and Mini models, specifically for smoother take-offs and more positive steering on wet or muddy roads.

undefined