# a3 sedan 2015 quattro - what haldex gen?



## iceorbital (Jul 2, 2011)

Does it have the same gen 4 as the 2012 Golf R, or the newest 5th gen? Any notable differences?


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## steve111b (Jun 2, 2011)

Gen 5.
There are two differences over the gen 4 - 2kgs lighter and the mechanical way in which it activates is different.
Will you notice any difference when you drive it compared to gen 4? I doubt it. Gen 5 has been out for a while and I have never heard anything about it being better/worse. There was talk of the gen 5 in the Volvos being a step backward, but I suspect that was a problem with Volvo not the haldex.
I have the gen 4 and it goes into action with any significant push of the throttle. Mostly people talk about wheel slip, but this applies more to the pre-gen 4 haldex.
For public roads the haldex is fine (especially snow/ice). Drivers, who take their cars on the track, may wish for a more RWD bias. On paper the maximum amount of rear drive is 50%, but in reality with the front wheels turned sharply on a snowy day you can get 100% to the rear.


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## Lpforte (Aug 2, 2011)

steve111b said:


> Gen 5.
> There are two differences over the gen 4 - 2kgs lighter and the mechanical way in which it activates is different.
> Will you notice any difference when you drive it compared to gen 4? I doubt it. Gen 5 has been out for a while and I have never heard anything about it being better/worse. There was talk of the gen 5 in the Volvos being a step backward, but I suspect that was a problem with Volvo not the haldex.
> I have the gen 4 and it goes into action with any significant push of the throttle. Mostly people talk about wheel slip, but this applies more to the pre-gen 4 haldex.
> For public roads the haldex is fine (especially snow/ice). Drivers, who take their cars on the track, may wish for a more RWD bias. On paper the maximum amount of rear drive is 50%, but in reality with the front wheels turned sharply on a snowy day you can get 100% to the rear.


Gen V is an actual step backwards though. The Gen IVs had a preloaded system so that it activated near instantaneously in low traction situations (hence why it works the moment you hit the throttle in your car). Gen V removed this for the weight savings you noted and reduced complexity. The effect though is that it does not activate nearly as quick. Will it matter for most driving situations? Probably not. But it is definitely a worse system now. There's no way to ignore the obvious mechanical changes that were made. That being said, no one has mentioned any traction/handling issues for the 2.0T/S3 so obviously it doesn't make much real world difference. We'll see once the snow starts falling.


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## davera3 (Jul 26, 2014)

I believe I read in the A3 literature that up to 100% of the power can be distributed to the back axle....

Yea, the page with "We found an exception to the rule of three. Four."..

"... it can transfer up to 100% of the torque to one of the two axles."

For that matter, if you believe it, they also mention torque vectoring as well.


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## jsausley (Dec 2, 2011)

It's not real torque vectoring - it uses the brakes.


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## gamegenie (Aug 24, 2014)

Question to all. 

How does the A3 Quattro compare to say Lexus IS 250 AWD?


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## araemo (Dec 9, 2012)

davera3 said:


> I believe I read in the A3 literature that up to 100% of the power can be distributed to the back axle....
> 
> Yea, the page with "We found an exception to the rule of three. Four."..
> 
> ...


An explanation of the torque split claim:
http://www.awdwiki.com/en/torque+split+ratio/

Basically, if the front wheels are fully slipping (0 traction), haldex locks the front and rear together (Basically it's a locking diff), so any torque applied has to be applied to the rear, if none can be applied to the front. This is not 'bad' - just not as 'good' if you want to intentionally drift your car.. and if you're on a track, having a bit of bias toward the rear helps avoid getting the fronts to that 0 traction point, so they can still be used to.. you know.. steer. 

So, it is still a downgrade from the top of the line quattro systems.. but from what I've been reading, even on the A4/S4, without the sport diff, the front and rear are both open diffs, and it uses brakes for torque vectoring the same as haldex.



jsausley said:


> It's not real torque vectoring - it uses the brakes.


I don't think using the brakes is as 'bad' as people think - most differentials that have a torque bias that I've read about use up some of the torque to create that bias anyways, so whether you're creating it by applying the brake or applying a clutch in the diff.. isn't that big a difference in most cases.

Would I prefer to have the S4 w/ the 40/60 'baseline' split and the sport diff? Maybe, once the B9 S4 comes out.. but I'm betting the price will get a bump, so I'll just be happy getting an S3 and getting 90% of the performance for less than 90% of the price.


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## steve111b (Jun 2, 2011)

Lpforte said:


> Gen V is an actual step backwards though.


You are correct, however I don't think that the speed of activation is a big issue these days.

Instead of being precharged (gen 4) the gen 5 will activate by the speed at which the pump can charge the clutch. How fast is the pump? Haldex does not usually give out numbers, so we will likely never know. There are many ways that Audi can choose to activate the haldex.

Take a look at the Crysler 200. The AWD is activated by the windshield wipers and when the temperatures fall below freezing. In both cases the speed of the pump (how quickly it activates) will not be a issue.


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## araemo (Dec 9, 2012)

steve111b said:


> Instead of being precharged (gen 4) the gen 5 will activate by the speed at which the pump can charge the clutch. How fast is the pump? Haldex does not usually give out numbers, so we will likely never know. There are many ways that Audi can choose to activate the haldex.


Also, just because it doesn't have a permanent pre-tension, doesn't mean it isn't normally pre-tensioned... It's electronically controlled, so it can be managed differently depending on drive select mode, throttle/steering position, and other inputs. I'd bet in 'economy' mode it would not be, but in dynamic, it would be (or would be more often).


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## davera3 (Jul 26, 2014)

araemo said:


> ...It's electronically controlled, so it can be managed differently depending on drive select mode, throttle/steering position, and other inputs. I'd bet in 'economy' mode it would not be, but in dynamic, it would be (or would be more often).


I have the drive select, but I dont believe there is a change in how the quattro reacts based upon that setting.

At least, nothing that Ive seen mentioned by Audi. Not saying youre wrong, mind you...


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## araemo (Dec 9, 2012)

davera3 said:


> I have the drive select, but I dont believe there is a change in how the quattro reacts based upon that setting.
> 
> At least, nothing that Ive seen mentioned by Audi. Not saying youre wrong, mind you...


Its conjecture on my part, so there's a decent chance I am wrong... I do know it takes speed into account, to make low speed maneuvering (parking...) easier.


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