For those of you who don’t know,
Haldex and Torsen are both great styles of All-Wheel Drive used in VAG Vehicles. In this article, I’ll use two cars, the Mk4 Volkswagen r32 & the B5.5 VW Passat to explain what the systems are, how they operate, and what their advantages and disadvantages are.
What are They?
The Haldex and Torsen style AWD Systems are commonly used in Volkswagen Auto Group applications (most prominently Volkswagen and Audi) to transmit torque from the power-plant to both axles. A good guideline if you’re wondering which style of AWD you have is, generally, Transversely mounted engines (Engines with Cylinders aligned “left-to-right”) use a Haldex System, while Longitudinally mounted blocks (Cylinders aligned “up and down”) use a Torsen System. Under the Audi marque, cars equipped with these technologies are branded as “Quattro”. Audi prominently uses the Torsen style drive system in its vehicles; AWD equipped Volkswagens are branded as “4motion”, and mainly use a Haldex system, there are some exceptions though.
How Do They Work?
To break it down, I’m going to use the example cars, and explain one system at a time.
Let’s take a look at our Volkswagen r32. The r32 has a Transversely mounted VR6 “r32” block, so Volkswagen implemented the front-drive based Haldex System. Under normal driving conditions, the r32 operates mainly as a front-wheel drive car, with about 95% of the power going to the front wheels. There is an electronically activated clutch which, once activated, will lock up and send up to 50% of the power to the rear wheels. The Haldex clutch is activated when the vehicle senses the front wheels spinning. The clutch allows for very little spin (15°) before engaging, allowing up to a 50/50 split in power, with the amount of power sent to the rear depending on how much, and if the front wheels are still spinning or not.
Our example vehicle for the Torsen AWD system is the B5.5 VW Passat 4motion, a platform-mate with the Audi A4 Quattro. The Passat is available with three Longitudinally mounted engines: A 1.8 liter turbo inline-four, a 2.8 liter 30v V6, and the unique 4.0 liter W8. Because of this, the Passat is a good platform for a Torsen style mechanical AWD system. A Torsen differential is a full time limited-slip center diff. used to vector torque to all corners. The Torsen differential is prominently mechanical, and is always active. Under normal driving conditions, the power is split 50/50 between the front and rear axles. When a torque imbalance occurs (eg. wheels spinning), the Torsen diff. can lock up, and is able to send up to 75% of the power (through, in this case, the Passat’s open front and rear differentials) to whichever axle needs it.
So, Which one is Better?
Ultimately, that decision comes down to personal preference. The overall consensus on Internet forums, in my experience, is that the Torsen system is the more highly revered style of AWD.
When it Comes to Drifting,
a Torsen style differential will result in a smaller radius and a cleaner drift due to its consistent power to the rears, and the ability to send up to 75% of that power there. However, once a drift is initiated, a vehicle with a Haldex differential is known to be easier to modulate and maintain a drift, while the Torsen’s transition from understeer-to-oversteer can make it difficult to hold a slide for a beginner.
Under Normal Driving Conditions
The downfalls of the Haldex style drive system include it’s dependency on electronics, resulting in loss of AWD from something as simple as a blown fuse or a faulty sensor. Also, a fault against the Haldex system is that because it is front-drive based, under normal driving conditions you have the added weight of AWD, without the power delivery, cornering, or engine braking benefits of All-Wheel drive when wheel spin is absent. The Haldex system also requires more frequent maintenance, but is still very commonly used due to its relatively small packaging and ability to be used with transversely mounted blocks.
If you guys made it the whole way through this post I’d like to thank you!
This is my first full length blog post so I hope it goes well. Hopefully I cleared up some things for you guys, if you have any more questions just ask me and I’ll do my best to answer them!