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Is the torque split 50/50 F/R on the A4 1.8 TQS?

B5QUAT Jan 17, 2012

  1. B5QUAT

    B5QUAT Member

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    Just wondering. Some 4wd systems, I believe, are either front or rear wheel biased and some are straight 50/50.

    What is the split on the B5 A4, does anyone know?

    Just out of interest as I just kicked the arse out on mine accelearting out of a junction. Behaved just like a RWD car normally does, only a bit more predictable and not quite as fierce. Just never had that happen before on a 4wd car. Used to driving understeery Imprezas. Got me wondering.

    Cheers
     
  2. aragorn

    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    The centre diff is a Torsen, which is a peculiar device and acts in some odd ways.

    What this means is that when you have full traction (or absolutely no traction) the diff acts as an open diff, and as a result sends power 50:50.

    When slip occurs, a torsen cannot fully lock, what it does is acts like a torque multiplier. So for instance when you launch the car you might apply 100lbft to each axle. The car hunches down, weight comes off the front axle and the front wheels spin up. At this point, the front wheels are still transmitting SOME torque to the road surface, and the Torsen can then apply twice this amount of torque to the rear axle. So the front might have enough grip to apply 50lbft to the road, and the torsen will then apply 100lbft to the rear in response until the slip stops.

    This is why with NO traction on one axle (say you've broken a shaft or become airbourne) the torsen will just act like an open diff, 2 x nothing is nothing.

    What it does mean though is as you've found you can get the arse out quite nicely in some situations. Typically wet roads or touching one wheel onto the gravel at the side of the road for instance can be enough for the torsen to shove a good chunk of the power rearwards and the arse then steps out. It'll often do it in snow as well.

    The newer torsens fitted to the B7 RS4 and other newer models have a greater bias ratio, they can put four times the front power rearward, and some companies offer modifications to some of the b5 diffs for a greater bias ratio.
     
  3. B5QUAT

    B5QUAT Member

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    Brilliant response, thanks for that. That explains the behaviour perfectly.

    These A4s are even more fun than I thought!
     
  4. Bradderz_1988

    Bradderz_1988 Dont replace it, Upgrade it !!

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    Yep had this in mine especially more this time of year and especially because I have my Pirelli tyres on the rear and maxxis on the front it tends to spin the fronts a lot.
     
  5. boost-addict

    boost-addict Active Member

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    i can only get my rear end stepping out on one slow tight corner in the wet, but with 225/45/18's it all straightens up soon enough after 10 feet lol
    not so much fun but i soon figure this is good, id love to see how these go on the track! just a shame theres loads of power loss via the system

    as for snow, i prey to god every night before bed that itll snow real bad like it did a few years back, because last two bad snow falls ive been driven a bloody bmw, rwd+snow = going no were. unless you let out all the air then maybe theres a chance!

    any way thanks for that post. some times i wonder if my plates need changing but dont know enough about the torsen or audis to know!

    still although ive never owned a audi nor a quattro or a 4wd/awd car before it was mighty strange feeling after driving bmws or even fwd cars, makes for good get aways out of junctions when its dam busy!
     
  6. aragorn

    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    Power loss is fairly insignificant tbh.

    Fuel economy is almost identical between my quattros and the old FWD A4 we had, even though the quattros are heavier.

    What people forget when they put a car on a dyno, is that a 2wd car still has another two wheels which are in contact with the road and causing resistance/drag, which are not measured on the dyno. Whereas with a 4wd car all four wheels are measured. Most of the additional power loss simply comes from the additional two wheels being added to the loss calculations.
     
  7. boost-addict

    boost-addict Active Member

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    ah i see, that makes sence, i suppose the 4wd does give a little more drag but then the 4wd then also has to word twice as less as the force of pushing the car is divided by 4. not sure if thats a corrcet assesment but my dyno sheet from the last owner showed 70hp loss.

    likley not correct so ive never belived it
     

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