Figure: lenta ru haldex vs torsen (17KB)
Lenta.ru did a comparison test of Audi TTS quattro DSG (Haldex automatic all wheel drive) and Audi A5 quattro automatic (quattro evolutions asymmetric Torsen-based full-time all wheel drive).
Under normal conditions – for example, city driving – one can’t feel the difference between Haldex and Torsen. Both Audi TTS and A5 accelerate well on compacted snow and slush. But if the car with an electronic clutch behaves like a front-wheel drive, accelerating without unnecessary tail happiness, the A5 has a strong rear wheel drive character, and keeps trying to go sideways. The ESP system allows some gliding and the driver has to compensate these movements by short steering wheel movements.
But when one goes on a twisty winter road, the differences in the all wheel drive design are more notable. If you accelerate out of a curve on Audi TTS with Haldex, the car understeers and does not let the driver to use thrust to skid the tail. The best this Coupe can do is to slide sideways, still missing the apex, but more often it understeers like a front wheel drive vehicle.
Therefore, we try to go through the same curve in another way... Our task is to make the rear axle slide in advance, by zig-zagging or using the handbrake. As soon as the car reacts to your actions and attempts to go into a drift – press the accelerator and try to draw an arc with the skidding of all four wheels by controlling the angle of skid by steering and accelerator. And you must be firm - to lock the coupling, you have to give the wheels more power than they can accept, causing them to slip. And if you do not, then the electronics will "help" you pull the car from skidding and puts more power to the front axle.
The TTS driver must constantly "play" with the gas pedal, causing wheel slip, and not allowing the car to become front-wheel drive once again.
Audi A5 with assymetrical "Torsen" behaves differently in a similar situation. Due to the fact that 60 percent of engine power goes to the rear axle, it is much easier to turn the car into the corner - you just need to press the gas pedal a bit harder. If the grip the front wheels had not yet been exhausted, the car immediately starts to drift. And to go in the "rally-style", you should only slightly reduce the fuel supply by releasing the gas pedal, and a little bit – but not completely – adjust the drifting by steering. Pure, mechanical happines!
But when under the wheels of the vehicle is compacted snow or ice, A5 with "Torsen" can behave just like his younger brother, TTS - in response to throttle the front wheels lose grip, and the car goes past the turn. In addition, A5 is heavier than TTS, so that all phases of sliding last longer and it does not respond as quickly as we would like to the actions of the driver.
If the car understeers, and the car stubbornly refuses to turn into a corner, then the driver has only one solution - almost completely let go of the gas, put the steering wheel straight and wait until the front wheels get grip. Once this happens - the rear axle will go a little further, triggering a light drift, and the car can be turned into the corner by using the accelerator.
But the main thing is - Audi A5 reacts even to the slightest change in the positon of the throttle, allowing to control the car very precisely, with the throttle, rather than the steering wheel. Haldex on TTS behaves quite differently – you don’t have to be sentimental with the gas. The higher the thrust, the clearer the car behaves. But in this case the ride turns into a struggle of human and the car’s electronic brain.
But most drivers are likely to find the behavior of Haldex TTS more familiar and safer than the habits of the car with "Torsen". This was confirmed by my colleagues, who drove both cars on snow-covered ground. According to them, TTS, in contrast to the A5, does not scare the driver off with a sudden drift in response to a throttle increase, and in order to cause a skid of the rear axle, it was much easier to "pull the handbrake," than to make themselves hit the gas pedal.
But I personally find myself closer to the mechanical "Torsen" - it has a character! It is interactive and involves the driver deeper in the process of driving. Yes, it requires attention to the slightest nuances in the behavior of the car and more accurate work with the gas pedal. But it is the character that we love in cars.