[A4] Re: Quattro, Torsen, Haldex and others...

Quincy Chiang b5quattro at shaw.ca
Tue Dec 28 16:08:44 EST 2004

If all 4 wheels are on shear ice with no traction whatsoever, then I can see how a quattro IV can be immobilised.  EDL brakes the side that's spinning more, but since the other side doesn't have enough traction to begin with, you're still not going anywhere.

I agree that the 38/62 split offers better balance in the dry, but I still don't like its inability to shift more power to either side.

I believe BMW introduced their new X-drive earlier this year, with the introduction of the X3.  I know they've since replaced the old system on the X5 with the new one, but I'm not sure if they ever adapted the x-drive to the e46 3-series, since the new 3 (e90) was just released very recently.  They may simply use the new system on the new 3.  I haven't read a lot on the X-drive, does anyone has any good info on that?

And speaking of the X3, I've read nothing but so-so to bad reviews on it.  It has a harsh ride due to high ride height combined with a stiff suspension for on-road handling.  Unless you absolutely need the ground clearance, you'll enjoy yourself much better in a 3-seriew wagon with AWD.  It's lighter, faster with better handling, braking and uses less fuel.  Also the interior looks kinda cheap to me.  I personally think BMW is diluting their image as an exclusive premium sport sedan/coupe maker by introducing SUVs in their lineup.  What's next, a BMW pickup and minivan?  Sorry for going off-topic!


----- Original Message -----
From: Rocky Mullin <caliban at sharon.net>
Date: Tuesday, December 28, 2004 11:48 am
Subject: Re: [A4] Re: Quattro, Torsen, Haldex and others...

> 	interestingly, i'm seriously considering an X3.
> At 8:29 AM -0800 12/28/04, Brian J White wrote:
> >"quattro IV - torsen center diff with open front and rear diffs,  
> but now it
> >has EDL to keep side-to-side traction in check.  This system  
> combines the
> >proactive nature of the mechanical torsen, with reactive aspect  
> of 
> >the EDL.  It
> >should in theory able to pass the "one wheel with  traction only" 
> test.">
> >Key point up there.  The car on which I saw the test applied was 
> a 
> >99 or so A4 Quattro...obviously having Quattro IV.
> >Either they disabled the EDL (possible as this was a marketing 
> >exercise) or the EDL couldn't keep up with absolutely ZERO 
> traction 
> >on the other 4 wheels.   It certainly looked like it was trying 
> but 
> >just couldn't make it happen.   My eyes popped out of my 
> head....I 
> >was certainly surprised to say the least.
> >
> >The BMW (the new system) AWD on the 330Xi certainly did the 
> trick. 
> >There are handling advantages to the 36/66 torque split as well. 
> >Biased towards the rear for that rear wheel drive track handling 
> >feel.
> >
> >
> >At 08:07 2004-12-28, Brizax at aol.com wrote:
> >>
> >>YEARS HUH? :)
> >>
> >>NYT is  wrong!!!
> >>
> >>On torsen based quattro system (now version 4, hence quattro  
> IV), the
> >>factory torsen is a splitted 2:1, meaning it can transfer up to 
> 2/3 
> >>of available
> >>power to either the front or rear axle.  I've read many  
> different 
> >>torque split
> >>figures from different sources, ranging from 40:60 to  30:70, 
> but I believe
> >>the 2/3 is the most correct.  There're other  versions of torsen 
> >>available, for
> >>example Stasis Engineering offers a 4:1  version, capable of 
> splitting up to
> >>4/5th (or 80%) to either end.
> >>
> >>All  torsen are normally 50:50, whereas the haldex quattro is 
> either 100:0 pr
> >>95:5  normally, and it's capable of sending all power to either 
> end.  Volvo
> >>uses this system as well.  So there, NYT got the 2 quattros  
> confused.>>
> >>Now here's some distinction of the different versions of  
> traditional quattro
> >>systems for longitudinally mounted engines (all B and C  chassis 
> cars, such
> >>as 4000, 80/90, 5000, 100/200, A4, A6, A8):
> >>
> >>quattro  I - original version.  All 3 diffs are open, but the 
> center and rear
> >>are  manually lockable.  It's very simple and reliable, but it 
> tends to eat
> >>tires or cause damage to the driveline when people forget to 
> unlock the diffs
> >>after they unstuck themselves.
> >>
> >>quattro II - introduced in '88 I  believe, when torsen replaced 
> the old open
> >>center diff.  The rear is  still manually lockable, but it's now 
> operated>>pneumatically so that it'll  unlock itself once the car 
> reaches 
> >>over 25 km/h.  I
> >>have this in my '90  CoupeQ, it works very well, never needed to 
> >>lock the rear
> >>diff, but this  version will not pass the "one wheel with 
> traction 
> >>only" test.
> >>
> >>quattro  III - this was only used in the V8, where both the 
> center and rear
> >>diffs are  torsen.  Since this car wasn't sold in large quantity 
> I don't know
> >>how  well it actually works, but it sure sounds promising, 
> almost like the
> >>HUMVEE's  system!
> >>
> >>quattro IV - torsen center diff with open front and rear diffs,  
> but now it
> >>has EDL to keep side-to-side traction in check.  This system  
> combines the
> >>proactive nature of the mechanical torsen, with reactive aspect  
> of 
> >>the EDL.  It
> >>should in theory able to pass the "one wheel with  traction 
> only" test.
> >>
> >>On the TT, its quattro system has no version  because it's not 
> an evolution
> >>of the original quattro for longitudinally  mounted engines.  As 
> I've said
> >>before, my brief drive in a TT didn't  impress me much.  I think 
> >>it's mainly due
> >>to the completely reactive  nature of the haldex system, ie, it 
> >>sends power to
> >>the rear until it detect  slips.  However I hear that Volvo has 
> >>since modified
> >>their haldex AWD on  newer cars and they're supposed to be a cut 
> above the
> >>original haldex  system.
> >>
> >>To further continue the AWD topic, BMW's system is not as good  
> as quattro
> >>due to its inability of changing torque split between front and  
> rear, it's
> >>always at 38/62.  However it's brand new x-drive is supposedly 
> >>much better than
> >>the old AWD system, which started in '88 in the 325ix and was  never
> >>changed/upgraded until just now.
> >>
> >>M-B's system is even  worse.  All 3 diffs are open and it relies 
> on their
> >>version of EDL to  control wheel spin by braking the spinning 
> wheel(s) hence
> >>sending power to the  ones that aren't spinning.  It's 
> completely 
> >>reactive, much
> >>worse than the  haldex system, and it places too much demand on 
> the 
> >>brakes.  If
> >>Audi  decided to deactivate their EDLs above 80 km/h due to 
> potentially>>overworking  the brakes, how well do you think M-B's 
> system copes 
> >>with this issue?
> >>  Although I must say this probably won't be a problem for daily 
> driving, it's
> >>  more of a problem if you really get stuck or actually to  off-
> roading.>>
> >>
> >>Now to chip in my $0.02 on the center versus rear  applications 
> of the torsen
> >>diff, they are really quite different.  Hence  if you've only 
> driven quattros
> >>with torsen center diff, you really have no  idea how it would 
> behave when
> >>is't slapped onto the rear of a RWD car, of the  front of a FWD 
> car 
> >>(I believe
> >>Nissan used to offer torsen on their 240SX and  Maxima as part 
> of their SE
> >>package).  A friend of mine (240SX owner) has  told me once that 
> having a LSD
> >>(such as torsen) in the rear is great in the  dry, but it does 
> do 
> >>some wierd stuff
> >>when it's wet and slippery, cause the  diff seems to be 
> distributing power
> >>from side to side as each of the rear  wheels lose and regain 
> >>traction during a
> >>turn.
> >>
> >>Anyhow, hope this clears  things up a bit, or not... ;-)
> >>
> >>Quincy
> >>'01.5 S4 - quattro IV
> >>'90  CoupeQ - quattro II
> >>
> >>
> >>
> >>
> >>_______________________________________________
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> >>A4 at audifans.com
> >>http://www.audifans.com/mailman/listinfo/a4
> >
> >
> >_______________________________________________
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> -- 
>  Rocky Mullin 
>  "Evil kills those who perpetrate it, and the pastures of 
> inequity are harmful"
>   http://www.rense.com/general37/char.htm

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