it kinda will but the EDL kicks in and stops the wheel spinning and effecivly feeds the power back to the wheels with grip.
How do you drive a quattro in snow & ice?
- Thread starter Hightower
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Torsen isnt open. Its a locking diff.
The diffs in the axles are open though.
So if one front wheel loses traction, the entire axle in effect loses traction (until EDL does its thing)
If you floored it on some sheet ice, you'd spin up one front and one rear wheel, again until EDL tried to help out.
The diffs in the axles are open though.
So if one front wheel loses traction, the entire axle in effect loses traction (until EDL does its thing)
If you floored it on some sheet ice, you'd spin up one front and one rear wheel, again until EDL tried to help out.
Apologies -- I stand corrected, Torsen is an LSD, quite a sophosticated system then
someone mentioned that the rear diff on a sport (quattro) was an LSD too
Yes I didn't make myself clear there. I should've added that if the rear axle has no grip either, then you're fecked and will do an E30 impression! :thumbsup:
Of course as mentioned our cars should have EDL and the ABS should apply the brakes to the spinning wheels to try and get some torque back to the the other axle/wheels but it practice (as a few of us know) it sometimes gets caught out.
I always feel safer with esp left on... however in the more mental conditions it wasn't any help at all... here is a thread I posted last year after an expedition to glenshee:
http://www.audi-sport.net/vb/showthread.php?t=67169
http://www.audi-sport.net/vb/showthread.php?t=67169
Not strictly true
No worries mate
To be fair, you said I'd be cruising past all the 2WD's so easilly I wouldn't need ice-capable tyres most of the time... and you were right on most of that
Still, I wouldn't mind a bit more grip than the Toyo Proxes are giving me... so just keeping an eye out for some more winter oriented tyres for my spare 16" wheels...
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My A4 2.0TQ has been a joy in the very ungritted icy snow covered roads up here in Strathclyde, I have always had to bare in mind the car outperforms most other similar cars in acceleration and control in this weather but braking is still a nightmare.
One thing that did catch me out was....I parked on my drive which sloes towards my hours, went into my house and stuck the kettle on, went back into the drive 5 mins later to find my pride and joy had slid down the drive and contacted the garage wall....it was my fault, had the handbrake on but never left it in gear.
the front wheels were on a small clear part of driveway but the back wheels were on ice. the front wheels turned freely while the locked back wheels slid.
Not having it repaired until after all this snow and ice clears as I'm now paranoid someone will slide into it soon as I get the job done....
One thing that did catch me out was....I parked on my drive which sloes towards my hours, went into my house and stuck the kettle on, went back into the drive 5 mins later to find my pride and joy had slid down the drive and contacted the garage wall....it was my fault, had the handbrake on but never left it in gear.
the front wheels were on a small clear part of driveway but the back wheels were on ice. the front wheels turned freely while the locked back wheels slid.
Not having it repaired until after all this snow and ice clears as I'm now paranoid someone will slide into it soon as I get the job done....
foolish3uk
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heres one to confuse the people who think they have just understood how the torsen diff works correctly lol. technically no haldex or quattro system is permanent 4 wheel drive, haldex is activated by control unit and quattro does not activate the rear diff untill approx 12mph, hence how audi can use normal rolling roads for mot's. (nothing is activated though the momentum of the spinning gears enables it all to work correctly in 4 wheel drive mode)
That sounds like Haldex, not Torsen.... pretty sure when mine was rolling roaded the back axle was driving right from the start.
foolish3uk
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haldex is electrically activated, quattro is mechanically activated! thats what i have put above. rolling road goes faster than the mot rollers.!
yes, agreed.... but front and rear are both driving from the start... I was just querying the statement...
pretty sure I was idling around on the ice and snow last week at <10mph and the back wheels were definitely driving
foolish3uk
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if you were idling how would you know the rear wheels were driving
at the vw national learing center there is a good demonstration tool they have that would demonstrate exactually how the quattro system works. it a a8 v8 genuine engine and gearbox which has been cut about and they have put perspex around all the important components and an electric motor to revolve all gears to show what happens. it clearly shows that when both front wheels are revolving in the forward or reverse direction that it is not untill that speed of approx 12 mph that the gears and torsen diff are int he correct position to transmit drive to the rear of the car!
at the vw national learing center there is a good demonstration tool they have that would demonstrate exactually how the quattro system works. it a a8 v8 genuine engine and gearbox which has been cut about and they have put perspex around all the important components and an electric motor to revolve all gears to show what happens. it clearly shows that when both front wheels are revolving in the forward or reverse direction that it is not untill that speed of approx 12 mph that the gears and torsen diff are int he correct position to transmit drive to the rear of the car!
They wont put torsen quattro on 2 wheell MOT rollers as they will dammage the centre diff ! Either that v8 model you seen in the vw museum was an older version or its not running well. Torsen quattro will transmit drive equaly between the axles, only when the centre diff senses slip then it will transfer power between the axles.
bit difficult to explain, but I was driving across a very icey slope and the back was sliding down the slope faster than the front of the car... so the back wheels ended up on some gravel further down the slope and kicked the car up the slope quite nicely... I'll take a bit more of a note next time though... certainly felt like the back was pushing me as the front was still on solid ice and had very little grip.
Sounds very dramatic, but I'd seen a few cars struggling through there (and getting in a fair mess earlier), so this was all at a slow walking pace (<5mph)...
It's around the corner form my folks' place, so I'll get a chance for a few re-enactments as it's always snowing and very bad ice where they live.
Sounds very dramatic, but I'd seen a few cars struggling through there (and getting in a fair mess earlier), so this was all at a slow walking pace (<5mph)...
It's around the corner form my folks' place, so I'll get a chance for a few re-enactments as it's always snowing and very bad ice where they live.
We have "proper" quattro. My MOT man took mine out with a decelerometer (sp) on the passenger seat as i made a point of telling him it was quattro.
The Haldex system will kick in at a standstill as soon as the ECU detects slip it will activate the rear diff, otherwise they would never be able to launch without just spinning everywhere on the front wheels.
The Haldex system will kick in at a standstill as soon as the ECU detects slip it will activate the rear diff, otherwise they would never be able to launch without just spinning everywhere on the front wheels.
foolish3uk
Registered User
the system we were working on was a new A8 and not in a mueseum, the national learing center is where all audi technicians go to college to learn everything about audis, and i was on the running gear specialist course! which is why they were going into great depth to try and explain how the torsen diff works!
lostbok, you are semi right, you were dragging the rear diff, so that will mesh up 4 wheel drive,
what i was aiming at is that if you were to turn the front wheels only under that speed you do not get four wheel drive!!! hence able to do mot's brake roller testing.
lostbok, you are semi right, you were dragging the rear diff, so that will mesh up 4 wheel drive,
what i was aiming at is that if you were to turn the front wheels only under that speed you do not get four wheel drive!!! hence able to do mot's brake roller testing.
foolish3uk
Registered User
byzan, if you have requested them not to put it on the rollers then they wouldnt do it anyway, you are correctt hey would use a decelerometer.
but do you think he has never done a quattro before, he must jnow that it can be rollered.
if by proper quattro you mean generation 1 it good to know that you have a ur quattro in working condition
there are about 4-5 different variations
but do you think he has never done a quattro before, he must jnow that it can be rollered.
if by proper quattro you mean generation 1 it good to know that you have a ur quattro in working condition
there are about 4-5 different variations
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You dont know what you talking about ! You cannot put a quattro/4x4 with a torsen centre diff on a 2 wheel rolling road as you will dammage the centre diff ! Gen5 tarsen as fitted to the new rs4 is biased so it will split the power 60-40 between the axles. I dont know what you seen but the quattro is allways intermeshed...only when wheels slips it locks up ! The rear and front diffs are open but if you brake a wheel(EDL takes care of it) it will transfer power to the other one wich doesnt slip.
foolish3uk
Registered User
oh mate after 15 years workin on audis i know exactually what im talking about, its about time that this age old mith is put to rest all that is left for me to say is 
It just doesn't make sense - in terms of traction, it certainly feels like the Quattro is working from completely stationary... we can try to get a demo video of that happening at <12mph for you, but just watch a Quattro pulling away on loose gravel - that'll do it for you
There are at least 10 versions of Audi's that bear the "Quattro" badge: 5 x Torsen and 5x Haldex... the A4-B6's use the Gen4 quattro system, so I'm guessing that covers the A8 that you were testing - that's the system that has been used on most larger Audi's from about 1999-2007.
Haldex has only been around for 10years (as opposed to 30+yrs for Torsen), but let's just say there was a lot more room for improvement with that one
There are at least 10 versions of Audi's that bear the "Quattro" badge: 5 x Torsen and 5x Haldex... the A4-B6's use the Gen4 quattro system, so I'm guessing that covers the A8 that you were testing - that's the system that has been used on most larger Audi's from about 1999-2007.
Haldex has only been around for 10years (as opposed to 30+yrs for Torsen), but let's just say there was a lot more room for improvement with that one
Doing brakes and oil services ? You have 3 torsen diffs in a quattro, 2 built in the gearbox and the rear diff. If you said the front is driven 1st why the car wont move IF you remove the propshaft off the gearbox ? In a conventional quattro with locking diffs, you can do just that. As the diffs on the quattro are efectively open, you need slip for them to engage. Thats why you loose traction if you only have traction across the car 1 wheel per axle. The car will move nowhere. Now, you dont have no transfer box to switch from low to high range like in a proper 4x4. I found a good test on the net a few months ago wich compared different 4x4 including some haldex and some torsens...Let me find it !oh mate after 15 years workin on audis i know exactually what im talking about, its about time that this age old mith is put to rest all that is left for me to say is
What is the Audi Quattro Four-Wheel-Drive System?
<LI id=jsArticleStep1 itxtvisited="1">The Audi Quattro four-wheel-drive system sends power to all four tires, giving it significant off-road and road-gripping capabilities. A four-wheel-drive system typically only sends power to both car axles when a toggle on the driver's dashboard is engaged, sending power to just the rear axle the rest of the time. This is because with standard open and locking differentials, it is difficult for a vehicle to turn on flat road when four-wheel drive is engaged. The Audi Quattro has found a way around this turning problem and developed a system that sends power to all four wheels all of the time. Technically, such a vehicle is labeled an all-wheel drive. Structure
<LI id=jsArticleStep1 itxtvisited="1">The structure of the Quattro four-wheel drive begins with the transmission. Ordinarily, four-wheel-drive cars feature a drive-transfer case with two drive shafts leading to differentials sitting between both the rear and front axle. Audi's version, however, does not have a drive-transfer case. In its place is a Torsen differential, from which extend two drive shafts. Each of those connects to a Torsen differential on each of the vehicle's axles. Mechanics
<LI id=jsArticleStep1 itxtvisited="1">Power passes through all three Torsen differentials to the wheels equally when the Audi Quattro is driving on a straight, smooth surface. The power is divided when there is more resistance on one wheel than another. For example, when the front passenger-side wheel edges off the road onto stiff gravel it puts more resistance against the wheel than the front driver-side wheel. This causes a shift in the power being sent to both wheels by the front-axle Torsen differential, sending more power to the driver-side wheel to compensate. Likewise, if both front wheels were to go off-road, the Torsen differential would send more power to the rear axle than the front.
<LI id=jsArticleStep1 itxtvisited="1">The Audi Quattro four-wheel-drive system sends power to all four tires, giving it significant off-road and road-gripping capabilities. A four-wheel-drive system typically only sends power to both car axles when a toggle on the driver's dashboard is engaged, sending power to just the rear axle the rest of the time. This is because with standard open and locking differentials, it is difficult for a vehicle to turn on flat road when four-wheel drive is engaged. The Audi Quattro has found a way around this turning problem and developed a system that sends power to all four wheels all of the time. Technically, such a vehicle is labeled an all-wheel drive. Structure
<LI id=jsArticleStep1 itxtvisited="1">The structure of the Quattro four-wheel drive begins with the transmission. Ordinarily, four-wheel-drive cars feature a drive-transfer case with two drive shafts leading to differentials sitting between both the rear and front axle. Audi's version, however, does not have a drive-transfer case. In its place is a Torsen differential, from which extend two drive shafts. Each of those connects to a Torsen differential on each of the vehicle's axles. Mechanics
<LI id=jsArticleStep1 itxtvisited="1">Power passes through all three Torsen differentials to the wheels equally when the Audi Quattro is driving on a straight, smooth surface. The power is divided when there is more resistance on one wheel than another. For example, when the front passenger-side wheel edges off the road onto stiff gravel it puts more resistance against the wheel than the front driver-side wheel. This causes a shift in the power being sent to both wheels by the front-axle Torsen differential, sending more power to the driver-side wheel to compensate. Likewise, if both front wheels were to go off-road, the Torsen differential would send more power to the rear axle than the front.
byzan, if you have requested them not to put it on the rollers then they wouldnt do it anyway, you are correctt hey would use a decelerometer.
but do you think he has never done a quattro before, he must jnow that it can be rollered.
if by proper quattro you mean generation 1 it good to know that you have a ur quattro in working condition
there are about 4-5 different variations
Yes i have torsion setup B5 TQS (gen 3 iirc with EDL), and i made a point of telling him as my last car was kitted as an S4 but only 2WD so i didnt want to risk the centre diff on the brake test.
I am sorry i am lost how i can possibly have drive on all 4 from a standstill but you say that you can drive one axle on a brake roller whilst the other is still on the ground. That seems to contradict the purpose of the whole system
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http://en.wikipedia.org/wiki/Torsen#Torsens_in_front_and.2For_rear_axles
The reason a torsen doesnt "Blow up" on a roller tester, is that the diff needs to have some torque applied across it to actually start to lock.
With a roller tester applying power to one side of it, it just acts like an open diff.
The same thing can be seen if you jack up one axle of a quattro and try to drive off, you'd just spin the wheels on the axle thats lifted off the floor and go nowhere.
The reason a torsen doesnt "Blow up" on a roller tester, is that the diff needs to have some torque applied across it to actually start to lock.
With a roller tester applying power to one side of it, it just acts like an open diff.
The same thing can be seen if you jack up one axle of a quattro and try to drive off, you'd just spin the wheels on the axle thats lifted off the floor and go nowhere.
foolish3uk
Registered User
Doing brakes and oil services ? :sign_unfair:QUOTE]
not everyone just does services, in fact us mastertechs barely do any at all!
i find that sort of comment very offensive!!!
you can research whatever you want on tinternet but that will not change the fact that if you put the car on a rolling brake tester the front wheels can move independently from the rear, (lets forget haldex, that is not 4 wheel drive until activated by the cntrol unit we all know that) if you have issues with this i suggest you look it up in official manuals and not by the old wives tales read on the net! IM BORED OF THIS NOW!
yes if you are on gravel and pulling away the car will be 4 wheel drive this is due to the forces acting on the diff. but in audi's development eyes the only true 4 wheel drive running gear setup as i know it is the Q7.
foolish3uk
Registered User
exactually aragon on rollers, handbrake on, turn front wheels and car will not try to lift off the rollers, as there is no torque across it! so this means that it is not 4 wheel drive at that particular moment, why do you think i put in my first post about confusing people that dont quite understand lol, because that would completely confuse them more
Here is a good material to read on how 4wd really started life:
http://www.rallycars.com/Cars/4wd_turbo_cars.html
http://www.rallycars.com/Cars/4wd_turbo_cars.html
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its not any wheel drive at that point... the engine isnt doing anything.
A landrover defender is 4wd, but the diffs are all open (without the centre difflock engaged) if you jack up ONE wheel, the truck wont go anywhere. Engage the centre difflock, and it will move, but if you then jack up one wheel on each axle, again you wont go anywhere.
A landrover defender is 4wd, but the diffs are all open (without the centre difflock engaged) if you jack up ONE wheel, the truck wont go anywhere. Engage the centre difflock, and it will move, but if you then jack up one wheel on each axle, again you wont go anywhere.
foolish3uk
Registered User
No mate, you dont understand your sentence. You are not driving the wheels of the cars with the engine you will drive them with the rollers, yes ? You keep stoping them in turn then you will just hear the EDS(diff lock) trying to stop the spinning wheel but the torque is not high enough to move the car forward. Spin the engine at 2000 rpm and you will hear and feel the centre Torsen diff locking up. You gave a bad example in the first place and dont forget the front diff on the Torsen audi is also an open viscous diff. You will do dammage by testing the brakes on 2wheel rollers thats why a good MOT garage will use an decelerometer to test brakes on these models. You must be one of them old school master techs -no offence mate but i have seen a big bunch of techs in dealers garages wich i wont trust them to wash me car let alone fixing it ! Your knowledge of the Audi marque might be beyond mine but i do know a thing or two about them and i dont call me a mechanic ! The Q7 is a propper 4WD as it has a low range box and locking diffs and its been perfected on the Cayene and Touareg. For a road going car the torsen quattro is the closest mechanical 4wd - without the use of locking diffs and transfer boxes - there is ! Read the last link i have posted and it might make you understand me statement !
to the ones who do know what they are on about!
I'm not taking side as I don't know enough but I'd like your comments.
In the brake test, if one wheel is moving i.e. the one on the roller, why doesn't the car apply the brakes to force torque transfer?
Isn't this the same type of scenario as if I parked with one wheel on ice or in a rut? Is it being suggested that one wheel on ice would mean you'd be stranded?
As mentioned at the start, I don't know the answer so would like to be educated on this.
FWIW I've always asked for my Torsen car not to be MOT'd on the brake machine. Maybe (I currently don't know!!) it wouldn't have made a difference but for someone who doesn't know it's obviously the safest bet as I don't see a down side.
In the brake test, if one wheel is moving i.e. the one on the roller, why doesn't the car apply the brakes to force torque transfer?
Isn't this the same type of scenario as if I parked with one wheel on ice or in a rut? Is it being suggested that one wheel on ice would mean you'd be stranded?
As mentioned at the start, I don't know the answer so would like to be educated on this.
FWIW I've always asked for my Torsen car not to be MOT'd on the brake machine. Maybe (I currently don't know!!) it wouldn't have made a difference but for someone who doesn't know it's obviously the safest bet as I don't see a down side.
Theres a difference between the brake test and the car powering the wheels
the RBT is driving the wheels at no more than 4mph
and the diff works when the engine is doing the driving
reading all this i think theres a hang up between the wheels being driven and the wheels doing the driving
also there seems to be a hang up between a Roller Brake Tester and a Rolling Road
The RBT drives the wheels and the RR gets driven its totally different and the diff works when its driving the wheel not when there being driven
as for the rest of the argument im not getting involved
Have Fun.
the RBT is driving the wheels at no more than 4mph
and the diff works when the engine is doing the driving
reading all this i think theres a hang up between the wheels being driven and the wheels doing the driving
also there seems to be a hang up between a Roller Brake Tester and a Rolling Road
The RBT drives the wheels and the RR gets driven its totally different and the diff works when its driving the wheel not when there being driven
as for the rest of the argument im not getting involved
Have Fun.
find a big car park! turn off the tc and let it rip! dont forget to close your window unless you want a face full of snow!!
