Porsche Macan ‘FAILS’ Moose Test – but there’s a reason (+video)Wed, 15 Oct 2014
The Porsche Macan locks its front brake in the Moose Test
The Moose (or Elk) test is a maneuverability and stability test commonly carried out in cold countries to test the behaviour of cars when subject to extreme avoidance tests – such as when trying to miss a Moose that’s wandered in to the road. The Moose Test is probably best remembered as the potential downfall of the original Mercedes A Class, when Teknikens Värld Magazine conducted a test on the then very new – and groundbreaking – high-riding A-Class, when it rolled over and cost Mercedes a small fortune in re-engineering to restore safety credibility to the A-Class.
Now it’s Porsche’s turn to come under the spotlight after Teknikens Värld ran a test on a Macan S Diesel that exhibited some strange behaviour during the test.
The Moose Test means driving a car at 70kph, serving to the left and then immediately to the right to test for stability. The Macan managed the left turn with ease, but when the testers turned right to get back on line the Macan momentarily locked its front left wheel and carried straight on. Teknikens Värld repeated the tests many times and got the same result.
Porsche responded quickly to the apparent failure of the Macan to complete the test safely, and say that the brake locking was a result of the Active Rollover Protection (ARP) kicking in for a maximum of 300 milliseconds to retain stability and stop the Macan from becoming unstable (full Porsche response to the Moose Test below the video).
It’s arguable that the interference of Porsche’s electronic wizards to keep the Macan stable were potentially hazardous – in a Moose Test situation – and certainly disconcerting for the driver, but it does seem that an instant extra on the wrong side of the road is preferable to a potential rollover.
Or is it?
The brake intervention shown in the video is a deliberately applied intervention to prevent the car from rolling over. This is called Active Rollover Prevention (ARP). The precise, momentary application of brake force to the front wheel at the outside of the bend down to the low slip range minimises cornering forces to avoid critical or instable driving conditions such as oversteer, rollover or detachment of the tyre from the wheel. Situations such as these may not be controllable by the driver.
The video shows that an understeer response is selected on purpose since it is significantly easier for the driver to control than oversteer. The function shown and the resulting driving response are explicitly desired to increase driving safety in such a highly dynamic driving manoeuvre.
In the SUV segment, Active Rollover Prevention (ARP) is state-of-the-art technology and is also used by other vehicle manufacturers.
The intensity of ARP intervention is dependent on vehicle speed and steering angle speed, among others. This means that ARP brake intervention is diminished accordingly at reduced vehicle speed or steering angle speeds. On the other hand, it means that the driving style adopted by Teknikens Värld was very demanding and resulted in the safety function being triggered.
Active Rollover Prevention is permanently active, irrespective of whether Porsche Stability Management (PSM) is on or off. If PSM is on, ARP intervention is significantly diminished since PSM brake interventions to stabilise the vehicle occur much earlier or are superimposed.
The function (ARP) is applied for a maximum of 300 milliseconds, depending on the driving situation. This short intervention ensures the directional stability of the vehicle. Lateral displacement is negligible. For this reason we do not regard this driving state as critical. As the video shows, lane changing can be completed stably and safely. What is more critical in this situation is if the vehicle were to roll over or the rear were to break away. The vehicle demonstrated none of these instable states (rollover, oversteer, wheel lift) at any time.
Porsche uses a comprehensive dynamics test programme which the Macan completed successfully. The driving manoeuvres performed include double lane change according to ISO, slalom with 10 x 18 metres and 10 x 36 metres, the VDA obstacle avoidance test which is very similar to the Teknikens Värld ”moose test”, and the NHTSA rollover safety test. All Porsche cars are designed for maximum safety based on these and other world-wide tests.
By Cars UK