# Audi TT rear wheel biased?



## lp01 (Dec 24, 2009)

Hi,
VW just launched the new Golf R with a drift mode which sends the majority of power to the rear wheels.
Considering the transmission of the Golf R is similar to, say, a TTS, do you think it would be possible (from a technical point of view over the existing haldex system) to program a rear biased mode in an existing TT/TTS?
That, IMHO, would be nice and something a lot of people would be willing to pay...
Regards


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## kevin#34 (Jan 8, 2019)

from a technical point of view might be even yes, if the Haldex controller is the same (I don't think so).... 
but programming the function is completely another story and I would say it would be impossibile, as DIY modification...


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## ross_t_boss (Feb 28, 2017)

First off - from what I have seen it doesn't send most of the power to the rear wheels, that is marketing tripe. It is similar to the Ford and AMG approach. It is still a power take-off, max. 50% bias - but it can direct power to either wheel with dual clutches. In that sense yes, you could have twice as much power to the outside rear wheel than each of the fronts (and that is how they get power oversteer for "drift mode").

As far at feasibility goes, I run a separate Syvecs Haldex controller, although it is CANBUS integrated... so in that respect its quite likely it could be controlled separately and thus retrofitted. But the true benefit is going to come with integration with ESP, torque vectoring, all the drift/track modes etc that won't be available - it'll be down to whatever an aftermarket controller does with the CANBUS inputs, and maybe some mobile app to change modes etc.

No doubt if it can be done someone will make something of it; personally I'll watch with interest but am looking at limited-slip differential options which will be better overall for performance anyway. There is a modified wavetrac option available for 3k but wavetrac should have a drop-in (allegedly) some time next year for half that.


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## macaddict111 (Jun 13, 2018)

The new Golf R nor any Haldex AWD model can't rear bias, this is probably some gimmicky marketing claim where it'll brake the inner front wheel during a hard drift/turn to try to get the rear to kick out on slick surfaces...


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## Roofchop (Sep 23, 2020)

I was thinking of this recently.

If a boffin could "lock up" the Haldex unit some how.

Then with 50% of drive going to the rear end it would be more tail happy for sure!

Probably.... :lol:


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## simestt (Nov 2, 2017)

You can't ever send more than 50% of the drive to the rear because there is no means of disconnecting the drive to the front. So, when the Haldex is fully locked (no slip) then the torque is split 50/50. However you can get the car to vary the way it sends torque to the rear using DriveSelect. The effects are subtle but if you set up an Individual setting with quattro=Dynamic, other settings same as you usually choose, then I think you will notice more drive to the rear. I suspect that setting quattro=Dynamic makes the torque split close to 50/50 in most circumstances. It's a pity Audi don't explain how it is actually programmed because it is certainly programmable.


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## leopard (May 1, 2015)

Why bother when you have excellence that is the new Toyota Yaris GR. It has permanent 4 wheel drive with three options on rear wheel transfer..


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## macaddict111 (Jun 13, 2018)

leopard said:


> Why bother when you have excellence that is the new Toyota Yaris GR. It has permanent 4 wheel drive with three options on rear wheel transfer..


Omg please tell me you're joking lolol


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## MarksBlackTT (Nov 29, 2016)

macaddict111 said:


> leopard said:
> 
> 
> > Why bother when you have excellence that is the new Toyota Yaris GR. It has permanent 4 wheel drive with three options on rear wheel transfer..
> ...


Nah, he's not joking. Does it to attract attention to himself. Probably suits a Toyota in any guise.


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## ZephyR2 (Feb 20, 2013)

Look it up. You can set front wheel bias, rear wheel bias or 50/50. All the pundits are raving about it. And for around £33k.


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## MarksBlackTT (Nov 29, 2016)

ZephyR2 said:


> Look it up. You can set front wheel bias, rear wheel bias or 50/50. All the pundits are raving about it. And for around £33k.


But it's a Toyota. A Yaris. Wouldn't dispute what it's capable of, extremely impressive in it's own right admittedly. But, very dubious as to whether anyone on here wants to be seen in one over their TT, even as a second car run-around.


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## ross_t_boss (Feb 28, 2017)

simestt said:


> You can't ever send more than 50% of the drive to the rear because there is no means of disconnecting the drive to the front. So, when the Haldex is fully locked (no slip) then the torque is split 50/50. However you can get the car to vary the way it sends torque to the rear using DriveSelect. The effects are subtle but if you set up an Individual setting with quattro=Dynamic, other settings same as you usually choose, then I think you will notice more drive to the rear. I suspect that setting quattro=Dynamic makes the torque split close to 50/50 in most circumstances. It's a pity Audi don't explain how it is actually programmed because it is certainly programmable.


Yeah, it's surprising how many peeps don't seem to get it. Simply put, the rear wheels can never spin faster than the fronts (on average across each diff, being open). No only that but it's a wet clutch so there are torque limits that come into play.

You can log Haldex pump duty which is a guide, it's not close to "locked" in most circumstances, but then it doesn't need to be - just enough to make sure the fronts don't spin at all. Above 3rd gear it's only locking up enough to push 10-20% power to the rear in many circumstances, unless it starts losing traction. Cruising and tight turning it's barely anything to the rear.

There are independent and piggy back controllers that give you control; wheels speeds (spin), steering lock, throttle position, boost, brake pedal, handbrake, hazards all utilised to change behaviour for example.


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## ZephyR2 (Feb 20, 2013)

MarksBlackTT said:


> ZephyR2 said:
> 
> 
> > Look it up. You can set front wheel bias, rear wheel bias or 50/50. All the pundits are raving about it. And for around £33k.
> ...


Wouldn't argue with that but it's worth reading up about it if you've looking to compare the TT haldex system with true 4WD. Which might be helpful to the OP.


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## leopard (May 1, 2015)

macaddict111 said:


> leopard said:
> 
> 
> > Why bother when you have excellence that is the new Toyota Yaris GR. It has permanent 4 wheel drive with three options on rear wheel transfer..
> ...


Except I'm not.. The Gazoo Racing Yaris driving gear is light years ahead and is a homologation special of their works rally car. It is contender for 2020 car of the year of any segment and is getting 5 star reviews across the board. Incidently It will leave a TT (s) or (rs) streets behind in any weather.






The point I'm making is the Haldex system isn't designed to be driven continuously, ie rear wheel driven as it's not substantial enough to do so. It is what it is, that is a system to kick in when slip is detected at the front wheels. For some people here who think they can turn a FWD into a BMW is comical.


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## leopard (May 1, 2015)

ZephyR2 said:


> MarksBlackTT said:
> 
> 
> > ZephyR2 said:
> ...


I would, you're too kind to the sop :lol:


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## powerplay (Feb 8, 2008)

ross_t_boss said:


> simestt said:
> 
> 
> > You can't ever send more than 50% of the drive to the rear because there is no means of disconnecting the drive to the front. So, when the Haldex is fully locked (no slip) then the torque is split 50/50. However you can get the car to vary the way it sends torque to the rear using DriveSelect. The effects are subtle but if you set up an Individual setting with quattro=Dynamic, other settings same as you usually choose, then I think you will notice more drive to the rear. I suspect that setting quattro=Dynamic makes the torque split close to 50/50 in most circumstances. It's a pity Audi don't explain how it is actually programmed because it is certainly programmable.
> ...


It's also amazing how so many motoring journalists get this completely wrong, not to mention even Audi/VW etc in their own marketing material, playing with words and mistakenly (deliberately?) saying Haldex can "send 100%" instead of "100% can mostly go" to the rear when it comes to the front wheels losing traction completely, which is the only scenario when the majority of the available torque is at the rear - only because there is no grip on half the drive train!


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## Gnasher (Oct 21, 2020)

It's not really a question of whether more torque goes to the front or the rear, but where that torque goes to at the rear.

The A45 AMG (and supposedly the Mk8 Golf R) have a drift mode, where (I guess) the haldex is locked to a 50/50 split and then the outer rear wheel is overdriven (by dabbing the brakes on the inside wheel) to induce oversteer.

I don't know whether this is better or worse than other ways to do it as it seems like it'll keep swapping the "dominant" end and keep switching between oversteer and understeer.


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## ross_t_boss (Feb 28, 2017)

GnasherTTRS said:


> It's not really a question of whether more torque goes to the front or the rear, but where that torque goes to at the rear.
> 
> The A45 AMG (and supposedly the Mk8 Golf R) have a drift mode, where (I guess) the haldex is locked to a 50/50 split and then the outer rear wheel is overdriven (by dabbing the brakes on the inside wheel) to induce oversteer.
> 
> I don't know whether this is better or worse than other ways to do it as it seems like it'll keep swapping the "dominant" end and keep switching between oversteer and understeer.


Half and half. You're right re: where torque goes, but on the new A45 and by the looks of it MK8 R the Haldex clutch is replaced by two clutches, one for each rear axle. This means that rather than using the brakes ("torque vectoring" on our cars) to overdrive the outside wheel, it actually can direct most of that 50% rear power to the outside wheel and traction. I'm not sure if mechanically that means it's overdriving the outer rear wheel, if so that certainly explains drift mode's capabilities!

I'm looking at LSD options - I'd like an off the shelf rear LSD which would pair nicely with my controller, it'll feel really nice under power, but really it's the front where its going to make the difference with lap times if one can embrace the FWD nature of the car.

That Yaris is an awesome piece of kit - I'd never have one but it would make an awesome local/shopping car (and weekend B-road hooning like no other).


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## leopard (May 1, 2015)

ross_t_boss said:


> it would make an awesome local/shopping car (and weekend B-road hooning like no other).


Certainly would. I'll let you know in the new year :wink:


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## ross_t_boss (Feb 28, 2017)

leopard said:


> ross_t_boss said:
> 
> 
> > it would make an awesome local/shopping car (and weekend B-road hooning like no other).
> ...


Nice one, look forward to the review! Don't get me wrong - if I had the use case I'd have one. I suspect it'll defy this hope on the limited numbers and spec, but low teens cost in a few years it has 'track slag' written all over it...

On a positive note for the OP at least with the GKN equivalent of this approach, as used in the Focus RS, I was reading they are "fully CAN integrated" which is means in theory someone could take the CAN inputs to the Haldex ECU and use them to run one - a conversion is possible but someone needs to create an ECU for it. Let's see if the new RS3 utilises this new VW offering, that would be a much better start place for such a swap.


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