# Haldex vs. Torsen



## VancouverA4 (Dec 30, 2000)

I believe Haldex is used in the A3/S3 and TT, while the Torsen system is used in other Audis. Is this solely a function of the transverse vs. longitudinal layout, or are there other reasons for the difference?
Which system is better? Which one allows for sportier driving?


----------



## billzcat1 (Sep 10, 2001)

*Re: Haldex vs. Torsen (VancouverA4)*

WELL this isn't a loaded question - good thing you aren't asking on the Q-list or you'd be banned for life!
My official position: Torsen good, Haldex good. Each has it's own merits. My personal favorite - quattro-I which used a locking center and a locking rear diff. Now for the dissertation on differentials....
Haldex is effective - a very effective computer controlled clutch system that beats any Viscous Coupling system since it locks up very quickly. From my understanding of the Haldex it biases the torque evenly 50/50 front/rear and this is ideal for cornering, helping keep some balance in the car w/ regards to over/understeer. The downside - it DOES take some time to react to slip and engage. It is also VERY dependant upon electronics and we ALL know how well VW/Audi electronics age








Torsen is a very ingenious little device - mechanically redistributing torque to the axle with the most available grip instantly, biasing up to 80% of the torque front/rear. This A) provides excellent straight-line grip in the most slippery of conditions and B)works proactively to prevent slip rather than reacting when slip occurs. Overall I think Torsen is the best all-around for the general public and is really quite good you can really thrash on it. The downside - the way most Audis are set up with regards to suspension, they tend to plow a bit. Consider that you are losing traction on the front wheels, the Torsen send the torque to the rear which perform 0 turning force and cause the car to push more. Not that the cars push uncontrollably but they are not as well balanced as they could be. Properly tuned suspension would help correct this.
Quattro-I has a locking center diff - this is great because the torque distribution of the Torsen is not a factor you can lock in the diff to split the torque 50/50 and so the drivetrain does not as adversely affect the handling characteristics. It becomes easier to tune the car's handling with a locking center diff. Note: all Audi's rallye cars used the locking center differential.
Hope this answers the question?


----------



## TabulaRasa (Aug 4, 2000)

*Re: Haldex vs. Torsen (billzcat1)*

Haldex is inferior! Under normal conditions the bias is more like 90% front, 10% rear.
Haldex requires 20 degrees of wheel slippage before the computer can detect and react to it.








Haldex can only move power between either the front or rear set of wheels, not send power to each individual wheel like TORSEN quattro does.


----------



## billzcat1 (Sep 10, 2001)

*Re: Haldex vs. Torsen (TabulaRasa)*

Actually Torsen quattro does not allocate power to each individual wheel - in most cases it distributes torque between the front and rear axle. In the odd case of the V8 quattro 5 speed there is also a Torsen diff in the rear which distributes torque side to side across the rear axle. In every case of quattro (even quattro-I) the front differential is open meaning more power is sent to the wheel that slips. The reason for this is that a limited slip device on the front axle would have a negative effect on A)tire wear and B)handling.
What Tabula _may_ be referring to is the current quattro-IV system which uses EDL - a form of traction control that limits the torque sent to each wheel utilizing the ABS brakes to actually brake the axle. This does not increase traction or distribute torque - it merely limits slip. In no system of quattro yet developed does the torsen diff distribute torque to each wheel.
Under normal conditions, Haldex is probably around 90% front, 10% rear. Under SLIP conditions it locks up and it is quite quick - for a part-time AWD system. Compare to Syncro or Subaru's Viscous Coupling systems....where they rely on a viscous fluid to lock two clutch plates together - under some conditions it may take a half revolution of the wheels before it locks up...20 degrees is pretty darn quick...but not as quick as Torsen (_or_ quattro-I) which are purely mechanical and have virtually no reaction time.
It is a case of reactive AWD (Haldex) vs proactive AWD (quattro)


----------



## VancouverA4 (Dec 30, 2000)

*Re: Haldex vs. Torsen (billzcat1)*

Can the Haldex system be set so that its say 70% to the rear and 30% to the front?


----------



## PerL (Jan 9, 2001)

*Re: Haldex vs. Torsen (VancouverA4)*

quote:[HR][/HR]Can the Haldex system be set so that its say 70% to the rear and 30% to the front?[HR][/HR]​No, maximum on any system that locks any type of center differential in any way is 50/50%. Only way to get more to the rear is when the front wheels are off ground.


----------



## Shomegrown (Feb 26, 2002)

*Re: Haldex vs. Torsen (billzcat1)*

quote:[HR][/HR]What Tabula may be referring to is the current quattro-IV system which uses EDL - a form of traction control that limits the torque sent to each wheel utilizing the ABS brakes to actually brake the axle. This does not increase traction or distribute torque - it merely limits slip.[HR][/HR]​I beg to differ. Actively braking one side of an openly differentiated axle will move torque over to the opposite wheel. This is the basis behind many AWD systems including the Merceedes M-Class. Let's say that the right hand side of an A4 Quattro was completely off the ground. An open system would simply spin the two right wheels that were not in contact with the road. With EDL, the airborn wheels would be slowed or stopped by the brakes, and torque would be transfered to the left side allowing the vehicle to move.

[Modified by Shomegrown, 11:15 PM 3-4-2002]


[Modified by Shomegrown, 11:15 PM 3-4-2002]


----------



## blkaudicq (Oct 22, 2001)

*Re: Haldex vs. Torsen (Shomegrown)*

With the new EDLs on the newer Audis, do the differentials actually lock or is it just a traction control system that brakes the slipping wheel(s), which sends power to the others (by way of open diffs)?


----------



## billzcat1 (Sep 10, 2001)

*Re: Haldex vs. Torsen (Shomegrown)*

You know I hadn't actually thought about the effect of selectively braking the sides of an open diff before...and you are correct sir! It is quite a system indeed! No wonder they have so much damn grip







Still not my preferred system for sporty driving tho....


----------



## blkaudicq (Oct 22, 2001)

*Re: Haldex vs. Torsen (billzcat1)*

Brakeing the wheels with the least traction is how traction control works. The Mercedes ML SUV has all 3 diffs open and relies on the traction control to let it move. I would rather have real locking/limited slip diffs.


----------



## Shomegrown (Feb 26, 2002)

*Re: Haldex vs. Torsen (billzcat1)*

I wholeheartedly agree. The Audi EDL system is really for low speed situations where very little traction is available. In fact, I think it becomes inoperative above 45 mph or so. While diverting torque, the system saps your momentum, by design. Another rear TORSEN or LSD would definitly be more favorable for spirited driving. http://****************.com/smile/emthup.gif


----------



## TORSEN TRACTION (Mar 27, 2002)

*Re: Haldex vs. Torsen (Shomegrown)*

hey you guys know a lot about the torsen! thats cool.
the torsen is superior to all differentails and i understand almost all about the torsen, considering that my grandfather invented it then we sold it to a company called zexel!
The Torsen has the highest torque biasing ratio of all limited-slip differentails.
if you have any questions ask!
i know that paragraph was messed up but its there!


----------



## blkaudicq (Oct 22, 2001)

*Re: Haldex vs. Torsen (TORSEN TRACTION)*

Alright TORSEN, I have always wondered, how does the center diff know which set of wheels have better traction? Does it actually "transfer" power of just lock 50/50?


----------



## IqDOU (Mar 24, 2002)

*Re: Haldex vs. Torsen (ALL)*

Great comments all!! Here's what I can add....

*blkaudicq:*
The Torsen differential distributes power by connecting the different axles by worm gears. In an open differential the axles are not connected which will not allow power to be distributed with differentiation between the axles. This is good for turning but bad for transmitting power. The Torsen differential uses worm gears to allow for SOME differentiation. On an Audi the selected worm gears are set at a bias ratio of about 3:1. This means that it can transmit power with UPTO a 3:1 differentiation between the axles...while an open is always at 1:1.
"Locking" the differential, as you state, would do the OPPOSITE of distributing power to the "gripping" axle.
*TabulaRasa & billzcat1:*
The Torsen set-up in most Audi's does not send power the individual wheel, just the axles. As bill said the only Audi that could send power to any specific wheel was the 5-spd V8's (and only the rears). By adding three Torsen diffs you could makes this possible. However the front bias ratio would have to be raised to allow proper differentiation. This would increase the friction in the drive-train and would not be beneficial. It would also be cost prohibitive.
*VancouverA4:*
Yes you can change the ratio. By placing smaller wheels on the front the car would "sense" slip and change torque accordingly. However, this may not be beneficial to the longevity of the Haldex system. Same is true for Torsen but you would take out some of your bias. In both cases you would be altering the dynamic characteristics of the car and I would not advise doing this.
*Shomegrown & billzcat1:*
EDL shuts off at 24mph. You two are DEAD-ON on how EDL works. While it is excellent on dry pavement at LOW speeds it is essentially worthless at a standstill in a snow bank. ie....Take that you high-sided the rear of the car in a snow bank. The rears are off the ground and can provide NO traction. EDL will brake the slipping "rear" wheels. The system is limited by Torsen and can only generate 3 times the torque that the brakes can hold. On dry pavement this would be plenty but with the rear in a snowdrift and the front on snow this will not be enough torque to pull you out. Also, on a quattro II car (pre-EDL) you could mimic EDL by pulling the e-brake, assuming it works








I will also state the EDL works great on slow corners in snow…BTDT
With that said I would take Torsen over any system out there followed closely by a locked center differential. Both are great it's just what you get used to driving
The moral: The key to Torsen is to keep it moving








I guess I can field questions too!! Cheers...


----------



## blkaudicq (Oct 22, 2001)

*Re: Haldex vs. Torsen (IqDOU)*

quote:[HR][/HR] Also, on a quattro II car (pre-EDL) you could mimic EDL by pulling the e-brake, assuming it works








[HR][/HR]​Or you could just hit the diff lock button.


----------



## IqDOU (Mar 24, 2002)

*Re: Haldex vs. Torsen (blkaudicq)*

quote:[HR][/HR]Or you could just hit the diff lock button.[HR][/HR]​No, in the case being discussed, locking the rear diff would have *NO* effect. This is just the nature of the Torsen differential and understanding how it functions would explain why this wouldn't help.

Simplest explaination that I can muster....
The easiest way to think of a Torsen differential is that the least traction _determines_ the total amount of traction (under slip conditions). With a bias ratio of 3:1 the maximum traction that can be applied by the gripping wheels is 3 times the *least* traction wheels.
If the car is high-sided then the least traction wheels would have ZERO torque (there is a small amount to spin the tires but that can be ignored). The front (gripping) wheels would have three times ZERO OR *ZERO* torque. Locking the rear differential would not help because you would still have ZERO torque at the rear wheels. However, if you pull the e-brake the torque needed to turn the rear wheels increases....thus the torque to the front (gripping) wheels increases by this amount *TIMES THREE*. In a snow drift this usually will not be enough to do anything.....but in the dry this may do the trick!! Hence my previous statments!!
Does that raise any additional questions?? Regards..


----------



## VancouverA4 (Dec 30, 2000)

*Re: Haldex vs. Torsen (IqDOU)*

Ok, I still have a question.
Does anyone know why Audi chose Haldex for the TT and A3/S3? If Torsen is better, why didn't they use it for these vehicles?


----------



## IqDOU (Mar 24, 2002)

*Re: Haldex vs. Torsen (VancouverA4)*

Torsional Rigidity....or lack there of!!
The A4 *platform* (notice that is platform NOT model) does not possess enough torsional rigidity to accept the Torsen differential. To make up for this Audi opted for the cheaper Haldex differential instead of reinforcing the chassis (this would increase wieght and cost)!!
NOTE: The A4 *platform* is used on the Audi TT/A3/S3 and VW Golf (possibly Jetta?). The Audi A4/S4 is built on the 8D *platform* (2002's are on the 8E platform)....as we know the "8-" type chassis do accept Torsen!!


----------



## Aw614 (May 9, 2001)

*Re: Haldex vs. Torsen (IqDOU)*

And the A8 is that Torsen?


----------



## IqDOU (Mar 24, 2002)

*Re: Haldex vs. Torsen (Aw614)*

Yes, the A8/S8 (4D platform), A6/S6/allroad (4B platform), A4/S4/VW Passat (8D, 8E platform) are Torsen equipped vehicles.
_ALL_ Audi's produced since 1988 are equipped with Torsen *EXCEPT* the 1990-1994 V8 automatic equipped cars and the TT's.


----------



## blkaudicq (Oct 22, 2001)

*Re: Haldex vs. Torsen (IqDOU)*

quote:[HR][/HR]Yes, the A8/S8 (4D platform), A6/S6/allroad (4B platform), A4/S4/VW Passat (8D, 8E platform) are Torsen equipped vehicles.
_ALL_ Audi's produced since 1988 are equipped with Torsen *EXCEPT* the 1990-1994 V8 automatic equipped cars and the TT's.[HR][/HR]​Ummm, no.







The V8s had TORSEN center AND rear diffs. I'm pretty sure they use the Haldex unit because it is easier to mount with the horiz. opposed engines.


----------



## IqDOU (Mar 24, 2002)

*Re: Haldex vs. Torsen (blkaudicq)*

I should have qualified my previous post. I was speaking for center differentials only and should have explicitly stated that!! For those who are curious here's the breakdown of the '90-94 V8's....
You are correct about the rear differential. ALL V8's have a Torsen rear differential. They also ALL have open front differentials.
However the center differential is dependant on the transmission used. The *AUTOMATIC* V8's have a wet clutch as a center differential. The *MANUAL* cars do use a TORSEN differential. 
I stated in my last post that there was no Torsen (should have stated center) differentials in the..."....1990-1994 V8 automatic equipped cars..."

Engine orientation makes no difference with Haldex. The Torsen differential is housed in the transmission case BEHIND the transmission and is not effected by the orientation of the engine.
Cheers...


----------



## D Clymer (Feb 18, 1999)

*Re: Haldex vs. Torsen (IqDOU)*

The reason the TT uses the Haldex is because the TT uses Golf drivetrain components. The Haldex system is an evolution of the old viscous syncro system with the viscous coupling replaced by the Haldex clutch. This was an easy change since the transmission didn't have to be modified to accept a front Torsen housing - which also wouldn't have been easy to package with the transverse transaxle shape. 
There are those who swear that the Torsen system is far less efficient, and doesn't react as quickly, but the Haldex system still spins the driveshaft at all times, so it can't be much more efficient. 
Looks like Audi has no plans of retiring the Torsen system. My prediction is that they will start using the new T3 Torsen center differential which has planetary gears which allow torque splits other than 50/ 50. A 45/55 split would certainly help to take a bit of that initial understeer. 
Now all they need to do is move the engines further back in the engine compartment, but of course that layout works perfectly for the Audi front drivers. Maybe they should just stop building front drivers.


----------



## 1996 Impala SS (Jan 6, 2002)

*Haldex also disconnects under braking/ down shifting. Torsen Does Not.*

Under a down shift in a haldex you are back to front wheel drive. The torsen will maintain an all wheel drive condition, much more balanced in this sitiuation. The Haldex must "see" slippage, a torsen will transfer torque before slipping happens.
www.torsen.com


----------



## Orjan (May 28, 1999)

*Re: Haldex vs. Torsen (TabulaRasa)*

quote:[HR][/HR]Haldex requires 20 degrees of wheel slippage before the computer can detect and react to it.








[HR][/HR]​Actually it's 15 degrees: <math-mode>An Audi TTq has 225/45-17 tires with a circumference of 1993mm. 15 degrees equals -> (1993/360)*15 = 83.04mm -> *3.27* inches of wheel spin</math-mode>


----------



## IqDOU (Mar 24, 2002)

*Re: Haldex vs. Torsen (Orjan)*

quote:[HR][/HR]Actually it's 15 degrees: <math-mode>An Audi TTq has 225/45-17 tires with a circumference of 1993mm. 15 degrees equals -> (1993/360)*15 = 83.04mm -> *3.27* inches of wheel spin</math-mode>







[HR][/HR]​<more math mode>
At 5 MPH (in a TT) you have 1.156 wheel rev/sec. 3.27 inches is 4.1% of a full revolution. Therefore, 4.1%/1.156 = 0.035 seconds to activate at 5mph.
At 1 MPH it takes a "whopping" 0.177 seconds!!
At 10 MPH it takes 0.018 seconds!!
</more math mode>
Pretty fast!!


----------

