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Thread: S3 how much power to rear wheels?

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    S3 how much power to rear wheels?

    Hi
    I would like to know how much power/torque can go to the rear wheels in the s3 when the fronts slip ? I googled it and it said 50/50 but I thought It was more? Or is it different again in normal Quattro models?

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    On haldex type AWD. Max that can be sent to the rears will only ever be 50%. Owing to the drive for the rears is taken from the offside output shaft from the gearbox.

    The torsen Quattro as found in longitudinally mounted Audis (a4/a6/a8 etc) uses a completely different system.
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    lastest gen haldex goes up to 70% alongside the Golf R
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    Thanks guys.

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    Quote Originally Posted by Sammyfat View Post
    Thanks guys.
    your welcome mate

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    This old chestnut again


    Before we start, its important to note that in the same way some Hi-Fi manufacturers refer to "peak" watts in marketing, the true measurable and comparable value should always be RMS Watts, so Haldex refer to "Torque" in marketing terms as "applied torque against a surface", rather than the more generic definition of Torque.


    The Haldex unit is a multi plate clutch device, capable of locking together the front (axle) drive and the rear (axle) drive. It is not a differential. Conceptually, it just joins the front half of the propshaft to the rear (propshaft).



    1. When engaged, can the Haldex ever change the 50:50 drive (front:rear) to be biased more to the rear?
    A: No. The Drive will always be, 100:0 (in the case of Haldex disengaged, FWD), or 50:50 (in the case of Haldex engaged, AWD).


    2. Can the Haldex ever cause the rear wheels to turn faster than the front (assuming equal friction surfaces for all tyres)
    A: No. Haldex can never make the car into a power-oversteering monster (assuming equal friction surfaces for all tyres)


    3. Can the Haldex "send" more than 50% of the torque to the rear?
    A: Yes (in Haldex marketing terms) eg: Front tyres are on a skating rink, rear tyres are on grippy tarmac.



    In Haldex world, you can't "send" torque. Torque in Haldex speak is what is being transmitted from tyre to ground.

    In the skating rink example above, the rear wheels will not be rotating faster than the front (ignoring the cross-axle diff), as the drive front:rear will be 50:50. But as the rears are gripping more than the fronts, then more torque is being transmitted by the rear wheels, than the front, and this will give you movement.

    In other driving situations and scenarios, you can set up the car to get all 4 wheels spinning and drifting, and yes, through driving and momentum, you can hang the back of the car out (for a period of time) - but on a dry grippy road, assuming equal traction at all 4 corners, most of the torque will be transmitted by the front tyres before it even thinks of going to the rears.

    Thats not to say that the car will always feel like a FWD car. Through careful setting up of the corner, you can utilise the fact that the rears are going to take a shorter path than the fronts (and turning slightly slower than the fronts), and you manually engage the Haldex to be ON, you can force the rears to turn at the same speed as the fronts, and you will "feel" the rears pushing.


    So. If you go by the definition that you define torque by what is being transmitted between tyre and ground, then yes, with a Haldex Unit, more torque can be available at the rear tyres than the front, depending on the friction (mu) of the surface.

    However, with the Haldex engaged, you can never have more than 50:50 drive (front:rear), and the rear wheels can never (in a straight line, equal mu surfaces) be made to turn faster than the front wheels.



    The following video illustrates torque transmitted at the tyres, as seen by Haldex.



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    I did try to search for the answer.... Thank you very much though, totally understand now.

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    i have first hand experience with that taking the Golf R to the race track how would you explain that in drags, we were chewing through toyo r888s' (rear tires) at a quicker rate in fact they were being chewed 3x as quick as the front and thats with the stock AWD system, just saying... here is a much more thorough and detailed view of the Golf R audi S3 haldex setup and the quattro set up in longitudinal A4 etc..

    have read you, i can assure you'll be interested

    Can someone explain the FWD Haldex system to me? - VW GTI MKVI Forum / VW Golf R Forum / VW Golf MKVI Forum / VW GTI Forum - Golfmk6.com
    Last edited by Sevv; 2nd December 2013 at 04:52.

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    I don't know how much more simply I can put this for you:

    It is impossible for the Haldex system in the VW Group vehicles, to deliver more than 50:50 drive, front:rear, when it is engaged.

    If my rear tyres were wearing faster than my fronts, I would consider suspension set-up, camber, toe in/out, pressures, etc., before jumping to the conclusion that the car suddenly became a power-oversteering rear wheel drive car.

    Besides which, as I alluded to above, if you drive around a track with the Haldex permanently switched on with soft tyres, due to the fact that the rear wheels are naturally going to take the shorter path around corners, but you are forcing them to drive at the same speed as the fronts, you will get an amount to tyre slip/scrub, and yes, this will lead to increased wear on the rears.


    Again: It is impossible for the Haldex system in the VW Group vehicles, to deliver more than 50:50 drive, front:rear, when it is engaged.
    (This is different to saying that up to 100% torque can be available at the rear driven wheels when the front wheels slip)



    Here are some graphs from the HPA Haldex Performance Controller. In every setting (Stock, Sport, Race etc.) - the line showing the power at the rear wheels NEVER exceeds the front wheels. Click on the graphs - they show a Golf on a AWD dyno. Bit more scientific than heresay and forum chatter.


    HPA Motorsports, Inc. - Haldex



    (Yes I did read the link you posted - if confirms what I am saying)
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    the set up was perfect so there is no other explanation, i wasnt talking about torque transfer either whilst its only 50:50 in relation to power transfer, all four wheel will be spinning the exact same speed but actually more torque to the rear is being achieved. and thats what that post talks about

    im talking of drags not going around corners either.. anyway its a good informed discussion for this forum so they know exactly what the haldex system is not quattro..

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    What is the effect of the front tyres being slightly more worn than the rears which is the normal case? Would this not cause some slippage of the rears as wheel rotational speed will not be the same?
    Steeve

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    The majority of the time, the Haldex clutch pack will be disengaged - so the car is normally in Front Wheel Drive.

    Only when the clutch pack is engaged, will the front tyres/rear tyres diameter matter, then yes, if you have got differently worn tyres, some slip/scrub will occur.

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    Quote Originally Posted by veeeight View Post
    This old chestnut again


    Before we start, its important to note that in the same way some Hi-Fi manufacturers refer to "peak" watts in marketing, the true measurable and comparable value should always be RMS Watts, so Haldex refer to "Torque" in marketing terms as "applied torque against a surface", rather than the more generic definition of Torque.


    The Haldex unit is a multi plate clutch device, capable of locking together the front (axle) drive and the rear (axle) drive. It is not a differential. Conceptually, it just joins the front half of the propshaft to the rear (propshaft).



    1. When engaged, can the Haldex ever change the 50:50 drive (front:rear) to be biased more to the rear?
    A: No. The Drive will always be, 100:0 (in the case of Haldex disengaged, FWD), or 50:50 (in the case of Haldex engaged, AWD).


    2. Can the Haldex ever cause the rear wheels to turn faster than the front (assuming equal friction surfaces for all tyres)
    A: No. Haldex can never make the car into a power-oversteering monster (assuming equal friction surfaces for all tyres)


    3. Can the Haldex "send" more than 50% of the torque to the rear?
    A: Yes (in Haldex marketing terms) eg: Front tyres are on a skating rink, rear tyres are on grippy tarmac.



    In Haldex world, you can't "send" torque. Torque in Haldex speak is what is being transmitted from tyre to ground.

    In the skating rink example above, the rear wheels will not be rotating faster than the front (ignoring the cross-axle diff), as the drive front:rear will be 50:50. But as the rears are gripping more than the fronts, then more torque is being transmitted by the rear wheels, than the front, and this will give you movement.

    In other driving situations and scenarios, you can set up the car to get all 4 wheels spinning and drifting, and yes, through driving and momentum, you can hang the back of the car out (for a period of time) - but on a dry grippy road, assuming equal traction at all 4 corners, most of the torque will be transmitted by the front tyres before it even thinks of going to the rears.

    Thats not to say that the car will always feel like a FWD car. Through careful setting up of the corner, you can utilise the fact that the rears are going to take a shorter path than the fronts (and turning slightly slower than the fronts), and you manually engage the Haldex to be ON, you can force the rears to turn at the same speed as the fronts, and you will "feel" the rears pushing.


    So. If you go by the definition that you define torque by what is being transmitted between tyre and ground, then yes, with a Haldex Unit, more torque can be available at the rear tyres than the front, depending on the friction (mu) of the surface.

    However, with the Haldex engaged, you can never have more than 50:50 drive (front:rear), and the rear wheels can never (in a straight line, equal mu surfaces) be made to turn faster than the front wheels.



    The following video illustrates torque transmitted at the tyres, as seen by Haldex.


    There is some misinformation here. First, there is always about 15-20% of torque at the rear wheels, it is never 0%, unless the rear is on glaze ice and the front has grip. This factoid used to be found on the Audi site too, under the lexicon section.

    Second, it is possible to apportion more than 50% of the torque to the rear axle even when the car is on a dry road with good grip at all 4 wheels. Haldex responds to differences in shaft speeds between the front and rear in order to eliminate slip. Dynamic weight distribution plays a huge role here. When you accelerate, the weight shifts rearward and the front axle slips imperceptibly (to the driver, but not the system). In most acceleration scenarios about 65/70% of torque goes to the rear axle, as anytime there is slip on the front diff, the power flows rearward. This also happens in cornering, as, in addition to the weight shift that goes on, the front wheels take a longer path than the rear. In many cornering scenarios the car will also have a rear torque bias.

    Furthermore, up to 100% of torque could be sent rearward if the front axle is on a very slippery surface and the rear isn't. The most important takeaway here is that there is almost ALWAYS slip on the front axle whether the road is wet or dry. So about the only time your car has 15-20% of torque at the rear is in steady state cruising at a constant speed, or in very low-speed parking maneuvers.

    A lot of this info. was provided by Ulf Herlin of Haldex on a different forum when a member wrote in to ask about the Haldex in his S3 8P.

    Lastly, the Gen. 4 Haldex on the facelift S3 pre locks the clutch pack unit, meaning that the car predicts when it will need to send large amounts of torque to the rear, and this makes the system proactive and capable of transmitting up to 50% of torque at any time. The difference between a Torsen and a Gen 4 (or the newer Gen 5 ) on the road is minimal, and the Haldex is actually faster to shift torque since it is electro mechanical and not purely mechanical.

    The only real difference on the road for the Torsen system is that the latest versions have a more rear-biased feel in some situations since the center diff now has 40/60 base configuration, but this is not really much different than the old 50/50 quattro or the latest Haldexes in driving feel.

    I have owned them all and the Gen 4 and 5 Haldex drive so similarly to the Torsens that it isn't even worth worrying about.
    Last edited by scherzkeks; 2 Weeks Ago at 10:15.

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    Quote Originally Posted by Sevv View Post
    i have first hand experience with that taking the Golf R to the race track how would you explain that in drags, we were chewing through toyo r888s' (rear tires) at a quicker rate in fact they were being chewed 3x as quick as the front and thats with the stock AWD system, just saying... here is a much more thorough and detailed view of the Golf R audi S3 haldex setup and the quattro set up in longitudinal A4 etc..

    have read you, i can assure you'll be interested

    Can someone explain the FWD Haldex system to me? - VW GTI MKVI Forum / VW Golf R Forum / VW Golf MKVI Forum / VW GTI Forum - Golfmk6.com
    Regarding rear tire wear, the reason your rears wore faster than the front is that with Haldex 4, the rears get about 70% in acceleration scenarios. Also the clutch pack can lock up independent of slip, so rear wheel engagement is much higher than on previous versions. My old S3 8P Sportback also wore through rear tires faster than the fronts by about 2mm on average, with even flat wear across the tire. See my post above for more...

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    Quote Originally Posted by scherzkeks View Post
    There is some misinformation here.
    There sure is. Here we go again. This isn't Pistonheads

    First, there is always about 15-20% of torque at the rear wheels, it is never 0%, unless the rear is on glaze ice and the front has grip.
    There will be some drag due to the viscosity of the clutch pack oil, this is where the 10-15% figure that Ulf Herlin talks about comes from. If you have a look at a graph of engagement, it is not proportional at all to the front over the entire rev range, this is simply oil drag, and not driven power.
    There is definitely no driven rear with the clutch pack disengaged, otherwise we would not be able to use the 2 wheel rolling road for brake tests at the MoT stations in the UK.


    Furthermore, up to 100% of torque could be sent rearward if the front axle is on a very slippery surface and the rear isn't.
    Even in Ulf Herlin's words, "near 100% torque transfer" (he nevers says 100%) - can happen, hypothetically. If your front wheels and no grip (ice rink) - AND the front of the car is suspended off the ground (no weight loading). As soon as the front end of the car is on the ground, with the weight of the front and engine on the wheels, that magical "near 100%" figure disappears. Even accounting for acceleration which lifts the front, you are not going to magically eliminate the weight off the front wheels. Therefore "near 100%" torque transfer to the rear is not possible in reality. Only for marketing purposes.

    Unless, of course, I happen to find myself with my front wheels on an ice rink AND suspended, whilst my rear wheels are on grippy tarmac



    The most important takeaway here is that there is almost ALWAYS slip on the front axle whether the road is wet or dry.
    I have no idea what you are talking about here



    This also happens in cornering, as, [.....].the front wheels take a shorter path than the rear

    Not in my world, they don't



    I have owned them all and the Gen 4 and 5 Haldex drive so similarly to the Torsens that it isn't even worth worrying about.
    In that case you can probably answer why all S3 8P's can always power oversteer out of corners?
    Last edited by veeeight; 2 Weeks Ago at 21:42.

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    Quote Originally Posted by veeeight View Post
    There sure is. Here we go again. This isn't Pistonheads



    There will be some drag due to the viscosity of the clutch pack oil, this is where the 10-15% figure that Ulf Herlin talks about comes from. If you have a look at a graph of engagement, it is not proportional at all to the front over the entire rev range, this is simply oil drag, and not driven power.
    There is definitely no driven rear with the clutch pack disengaged, otherwise we would not be able to use the 2 wheel rolling road for brake tests at the MoT stations in the UK.
    It is clutch pretensioning, and it means that 15% of the torque is on the rear wheels. The Haldex fully disengages on braking as it is electronically triggered to do so, and there is no reason for it to stay engaged. It does not disengage fully when cruising on a motorway.

    Quote Originally Posted by veeeight View Post

    Even in Ulf Herlin's words, "near 100% torque transfer" (he nevers says 100%) - can happen, hypothetically. If your front wheels and no grip (ice rink) - AND the front of the car is suspended off the ground (no weight loading). As soon as the front end of the car is on the ground, with the weight of the front and engine on the wheels, that magical "near 100%" figure disappears. Even accounting for acceleration which lifts the front, you are not going to magically eliminate the weight off the front wheels. Therefore "near 100%" torque transfer to the rear is not possible in reality. Only for marketing purposes.
    It is possible in reality, just unlikely. The more important figures are found in the dynamic weight distribution scenarios I mentioned, as this is where AWD is needed most.

    Quote Originally Posted by veeeight View Post
    I have no idea what you are talking about here
    There are a variety of factors that cause slip in the front diff, and there is rarely a state in which you are driving where the front is not registering some degree of slip.


    Quote Originally Posted by veeeight View Post





    In that case you can probably answer why all S3 8P's can always power oversteer out of corners?
    Since the system matches axle speeds, this would be impossible. Just as it is with a Torsen 50/50 or any system that does not overdrive the rear. In some regards Torsen cars are also more prone to understeer than Haldex cars, but it depends on what section of the corner you are talking about, and what the driver inputs are.

    I'm not exactly sure which of the 3 PH stalkers you are, but I do find it amusing that you are now integrating information that I brought up in past threads (that you challenged) on that site and passing it off as information that you always knew and accepted as fact. At least you appear to be learning something.

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    Quote Originally Posted by scherzkeks View Post
    It is clutch pretensioning, and it means that 15% of the torque is on the rear wheels. The Haldex fully disengages on braking as it is electronically triggered to do so, and there is no reason for it to stay engaged. It does not disengage fully when cruising on a motorway.
    This is clutch drag, not engagement. It is not a constant 15%. it is only 15% at a specific rev, tapering to less than 10% at 5000rpm. Look up the engagement graphs for yourself, always better than forum heresay. Once again, if it is engagement, use of the 2 wheel brake test rolling road would be impossible as the car would be trying to jump off the rollers. This does not happen.

    Additionally - clutch pretensioning only possible on Gen 4 & 5. Ulf wrote that email back in Gen 2 days, before pretensioning. That blows the 15% engagement out of the water.


    It is possible in reality, just unlikely. The more important figures are found in the dynamic weight distribution scenarios I mentioned, as this is where AWD is needed most.
    Exactly when will I find myself with my front wheels with no weight on them, and rears on grippy tarmac?
    "Near !00%" torque transfer to the rear is a marketing scenario, not reality.


    There are a variety of factors that cause slip in the front diff, and there is rarely a state in which you are driving where the front is not registering some degree of slip.
    These are your words - "The most important takeaway here is that there is almost ALWAYS slip on the front axle whether the road is wet or dry". Demonstrate this in a straight line, with equal high friction surface on all tyres please.


    I think you didn't detect the sarcasm of the oversteering S3 scenario. It was a reference to how you found Haldex so similar to Torsen that it wasn't worth bothering with the difference. Nevermind.


    I'm not exactly sure which of the 3 PH stalkers you are, but I do find it amusing that you are now integrating information that I brought up in past threads (that you challenged) on that site and passing it off as information that you always knew and accepted as fact. At least you appear to be learning something.
    I have no idea what you are talking about. I am not a member of PH, and have never posted there. I just occasionally read some of the far fetched scenarios on there.
    Why, have you got previous form for rubbish on there ?
    Last edited by veeeight; 2 Weeks Ago at 23:05.

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    Quote Originally Posted by veeeight View Post
    This is clutch drag, not engagement. It is not a constant 15%. it is only 15% at a specific rev, tapering to less than 10% at 5000rpm. Look up the engagement graphs for yourself, always better than forum heresay. Once again, if it is engagement, use of the 2 wheel brake test rolling road would be impossible as the car would be trying to jump off the rollers. This does not happen.

    Additionally - clutch pretensioning only possible on Gen 4 & 5. Ulf wrote that email back in Gen 2 days, before pretensioning. That blows the 15% engagement out of the water.
    So it is either 15% or 15% that can tapers down to 10%. Even assuming you are right (which I know you are not, as the 15% figure has been published by Audi AG), I don't see the issue.

    As for the rest, you clearly don't even understand how your own MOT RR dynos work for brake testing.
    Quote Originally Posted by veeeight View Post
    Exactly when will I find myself with my front wheels with no weight on them, and rears on grippy tarmac?
    "Near !00%" torque transfer to the rear is a marketing scenario, not reality.
    What exactly is your point? The mechanical ability to do so is there, and this extreme example illustrates the greater concept -- that under slip, more than 50% of torque passes rearward. Do you actually have trouble comprehending this?

    Quote Originally Posted by veeeight View Post

    These are your words - "The most important takeaway here is that there is almost ALWAYS slip on the front axle whether the road is wet or dry". Demonstrate this in a straight line, with equal high friction surface on all tyres please.


    I think you didn't detect the sarcasm of the oversteering S3 scenario. It was a reference to how you found Haldex so similar to Torsen that it wasn't worth bothering with the difference.
    1. The key word is "almost." Too subtle?

    2. In my opinion the systems are virtually interchangeable as sold in current Audi products. You aren't doing power oversteer with a 50/50 Torsen, nor with the 40/60, unless you have a sport diff -- and even then it is effort. I should know, I have one.



    Quote Originally Posted by veeeight View Post


    I have no idea what you are talking about. I am not a member of PH, and have never posted there. I just occasionally read some of the far fetched scenarios on there.
    3/10

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    Quote Originally Posted by scherzkeks View Post
    as the 15% figure has been published by Audi AG
    Then you can provide a link, or document. You must be getting confused with Gen2 Haldex.


    1. The key word is "almost." Too subtle?
    Yes. Especially seeing as Gen 2 Haldex required 15 degrees of wheel slip to couple. "Almost" doesn't cut it.


    2. In my opinion the systems are virtually interchangeable as sold in current Audi products.
    One is a full time all wheel drive system, the other is a part time all wheel drive system. Too subtle? Or just difficulty comprehending?
    You would be a genius in the marketing department, actually you could save them a shed load of money by fitting Haldex to the RS6 if it's "virtually interchangeable".


    3/10
    Again, I have never posted on PH. I'm not one of your so called stalkers. Paranoia?

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    Quote Originally Posted by veeeight View Post
    Then you can provide a link, or document. You must be getting confused with Gen2 Haldex.

    For Gen. II, the amount of rear wheel engagement varied by manufacturer and even among models in the range. Audi previously stated 15% on their old website under the lexicon. Other than that, you have a link already -- Herlin confirms between 10-15% for the Gen. II and points out that this amount of torque is enough to stabilize the car and also reduce fuel consumption when large amounts of rear torque are not needed.

    A side note though, the Gen IV is completely different. It uses the same pretension on start up of about 15%, but uses a seperate electronic pump to keep the accumulator full , so when one accelerates or when the system deems otherwise necessary, full locking torque is available immediately, rather than the system having to build pressure to effect more clutch lockup.
    Quote Originally Posted by veeeight View Post

    Yes. Especially seeing as Gen 2 Haldex required 15 degrees of wheel slip to couple. "Almost" doesn't cut it.
    False. Wheel spin is not the same as slip on the axle. In a normal acceleration scenario with good grip on all four tires and a dry road, we know for a fact that more than 50% of torque can and does go to the rear axle with no wheel spin, due to slip from dynamic weight transfer. The lag from detection to engagement is the reason why Gen. II would sometimes exhibit a small amount of wheel spin, as the system did not have enough instantaneous pressure available to fulfill the amount of toruqe requested by the ECU.


    Quote Originally Posted by veeeight View Post
    One is a full time all wheel drive system, the other is a part time all wheel drive system. Too subtle?
    No, just flat out wrong. Full time does not denote a 50/50 or any torque split. It denotes that the system is working at all times, which all Haldex generations do. The word you seek is proactive, which Gen. II was not, since it could not always supply enough torque instantaneously to meet ECU demands -- an issue that sometimes manifested itself to the driver in "seesaw" like transitions from under to oversteer in on-the-limit handling.
    Last edited by scherzkeks; 2 Weeks Ago at 10:01.

  22. #21
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    Quote Originally Posted by scherzkeks View Post
    Audi previously stated 15% on their old website under the lexicon. Other than that, you have a link already -- Herlin confirms between 10-15% for the Gen. II
    Fact is, there is no official Audi document stating a 85/15 split. This is just forum heresay, and that is where you appear to have picked it up from.

    Herlin does not speak for Audi calibration, he is/was VP Marketing.

    So are you accepting that Gen 4 has no 85/15 split ? And is actually 100/0 (or 95/5) ?

    Once again, you have failed to prove any doumentation from Audi regarding this fictitous 85/15 split.



    we know for a fact that more than 50% of torque can and does go to the rear axle with no wheel spin, due to slip from dynamic weight transfer.
    You ae confusing fact, with your opinion or supposition.
    Provide calculations of the weight distribution of the car while static, and dynamically under acceleration. I doubt that it changes such that over 50% torque transfers to the rear on an equal friction surface.


    Haldex is not, and will not be, including Gen V, a full time AWD system. If this was the case, the clutch packs would be burnt out and overheated in no time at all with a constant slip on the clutches. It may be working all the rime, but it certainly is not engaged all the time. You are plain wrong and misinformed.

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