MK1 Audi TT Opinions?

Rusty911

A2OC Donor
Yes, that's right. The gearbox in the TT drives the front wheels just like a front wheel only drive car. The difference is that it has a additional output shaft that goes through a transfer box to the Haldex clutch. The clutch controls how much power goes to the rear wheels so for most of the time its more or less like a front wheel drive car. When the front wheels loose grip, the ECU engages the Haldex clutch and directs power to the rear wheels but it can be only a maximum of 50% as the front wheel drive is permanently connected. The problem with the standard set up is that it takes up to 4 revolutions to fully engage the Haldex. As this happens after the front wheels have lost grip, there is a noticeable delay before the rear kicks in. A common mod for Haldex cars which I have on my Mk1 TT is to reprogram the Haldex ECU to engage the rear drive on the throttle. When applying power, the rear drive engages straight away and so before the front grip is lost. This means you can power out of corners and have the back of the car push you round the bend with a little bit of controllable oversteer if you want. That completely transforms how the car drives.

regards

Andrew
That's fasinating, thank you: I'd not heard of that particular upgrade.

I wonder, have you done the DEFCON mod or the offset rear bushes / caster increase?

I'm not normally into modding, but to turn the TT back into the car is was originally designed to be (more driver orientated) does appeal.
 

Edwrai

Member
Yes, that's right. The gearbox in the TT drives the front wheels just like a front wheel only drive car. The difference is that it has a additional output shaft that goes through a transfer box to the Haldex clutch. The clutch controls how much power goes to the rear wheels so for most of the time its more or less like a front wheel drive car. When the front wheels loose grip, the ECU engages the Haldex clutch and directs power to the rear wheels but it can be only a maximum of 50% as the front wheel drive is permanently connected. The problem with the standard set up is that it takes up to 4 revolutions to fully engage the Haldex. As this happens after the front wheels have lost grip, there is a noticeable delay before the rear kicks in. A common mod for Haldex cars which I have on my Mk1 TT is to reprogram the Haldex ECU to engage the rear drive on the throttle. When applying power, the rear drive engages straight away and so before the front grip is lost. This means you can power out of corners and have the back of the car push you round the bend with a little bit of controllable oversteer if you want. That completely transforms how the car drives.

regards

Andrew
Haldex mk1 is 1/4 of a wheel rotation


Haldex Generation I and II based all wheel drive system is reactive. The coupling activates after a wheelspin is detected. However, the reaction is very quick and just 1/4 of a wheel turn is needed to engage all wheel drive. Electronics is capable of lowering the oil pressure only (when parking, ABS working, the handbrake is pulled, etc.), but cannot pre-tension the clutch.


Sent from my iPhone using Tapatalk
 

PlasticMac

Member
There are various mods for the Haldex, both mechanical and electronic, including open source material and multi mode (track comfort etc). TT Forum is worth a browse if that's your fancy.
Mac.
 

ajsellors

A2OC Donor
Haldex mk1 is 1/4 of a wheel rotation


Haldex Generation I and II based all wheel drive system is reactive. The coupling activates after a wheelspin is detected. However, the reaction is very quick and just 1/4 of a wheel turn is needed to engage all wheel drive. Electronics is capable of lowering the oil pressure only (when parking, ABS working, the handbrake is pulled, etc.), but cannot pre-tension the clutch.


Sent from my iPhone using Tapatalk
Thanks, I remembered the 4 bit right, 1/4 of a turn makes more sense. The other difference that the software I have makes is that the rear drive remains engaged during hard braking for extra stability. The standard software always disengages the rear drive as soon as you touch the brakes.
 

Edwrai

Member
Thanks, I remembered the 4 bit right, 1/4 of a turn makes more sense. The other difference that the software I have makes is that the rear drive remains engaged during hard braking for extra stability. The standard software always disengages the rear drive as soon as you touch the brakes.
The one that remains engaged on brakes is the track use one, if I remember correctly


Sent from my iPhone using Tapatalk
 

Rusty911

A2OC Donor
Haldex mk1 is 1/4 of a wheel rotation


Haldex Generation I and II based all wheel drive system is reactive. The coupling activates after a wheelspin is detected. However, the reaction is very quick and just 1/4 of a wheel turn is needed to engage all wheel drive. Electronics is capable of lowering the oil pressure only (when parking, ABS working, the handbrake is pulled, etc.), but cannot pre-tension the clutch.


Sent from my iPhone using Tapatalk
The video I saw (and now can't find) showed fast snowy starts in slo-mo on MK1 TT and a large platform Audi of some sort running Torsen. The latter simply fired up all wheels instantaneously, the former clearly showed the slight delay. Even so, both fired off the line very effectively!

What I'm not so clear on is why, having put the facility to drive all four wheels on to a car, you wouldn't use it more of the time by default? Why is it more economical to (virtually) just drive the front wheels with rear propshaft and driveshafts spinning free, than simply driving the lot as a matter of course? The kinetic load and weight is the same. Is there a diff missing from the Haldex system compared to the Torsen?
 

Rusty911

A2OC Donor
Thanks, I remembered the 4 bit right, 1/4 of a turn makes more sense. The other difference that the software I have makes is that the rear drive remains engaged during hard braking for extra stability. The standard software always disengages the rear drive as soon as you touch the brakes.
Any downsides to the software that you've found?
 

Jeetesh

Member
The video I saw (and now can't find) showed fast snowy starts in slo-mo on MK1 TT and a large platform Audi of some sort running Torsen. The latter simply fired up all wheels instantaneously, the former clearly showed the slight delay. Even so, both fired off the line very effectively!

What I'm not so clear on is why, having put the facility to drive all four wheels on to a car, you wouldn't use it more of the time by default? Why is it more economical to (virtually) just drive the front wheels with rear propshaft and driveshafts spinning free, than simply driving the lot as a matter of course? The kinetic load and weight is the same. Is there a diff missing from the Haldex system compared to the Torsen?
The main difference in VAG vehicles is the mounting of the engine, if it’s traverse (left-right) then these cars use a Haldex system for 4wd. If the engine is longitudinal (north-south) then they use the torsion system.
FWD cars typically are traverse engined and therefore the Haldex arrangement works for adding 4wd to those cars. They are however always predominantly FWD.
The torsion arrangement typically sends torque to all 4 wheels on a 50/50 front rear arrangement and is effectively always 4 wheel drive and then software apportions torque accordingly based on loads of parameters.

In answer to your question then the different arrangements are used for the purpose of packaging and fuel economy (and cost) and whilst yes it weighs the same the Haldex system if the software was programmed to make it permanently 4wd would result in anywhere between 5-8 mpg less together with increased CO2. When you are making a golf and all the lesser versions don’t need 4wd your back to cost vs packaging.

Packaging is such a big thing in small cars that the new BMW 1 series is now front wheel drive yet the previous one shared most of the mechanicals with the 3-series. The current one shares it mechanicals with a mini!

Have a read of the engineering behind the new merc A45S And how that works and it’s truly brilliant but comes at a cost.
 

Rusty911

A2OC Donor
The main difference in VAG vehicles is the mounting of the engine, if it’s traverse (left-right) then these cars use a Haldex system for 4wd. If the engine is longitudinal (north-south) then they use the torsion system.
FWD cars typically are traverse engined and therefore the Haldex arrangement works for adding 4wd to those cars. They are however always predominantly FWD.
The torsion arrangement typically sends torque to all 4 wheels on a 50/50 front rear arrangement and is effectively always 4 wheel drive and then software apportions torque accordingly based on loads of parameters.

In answer to your question then the different arrangements are used for the purpose of packaging and fuel economy (and cost) and whilst yes it weighs the same the Haldex system if the software was programmed to make it permanently 4wd would result in anywhere between 5-8 mpg less together with increased CO2. When you are making a golf and all the lesser versions don’t need 4wd your back to cost vs packaging.

Packaging is such a big thing in small cars that the new BMW 1 series is now front wheel drive yet the previous one shared most of the mechanicals with the 3-series. The current one shares it mechanicals with a mini!

Have a read of the engineering behind the new merc A45S And how that works and it’s truly brilliant but comes at a cost.
Yes, 2 Series has been Mini based for years.

Respectfully, actually the Haldex system by default is essentially FWD (90/10, 95/5 or 100-0% depending on version and where you read it seems! ). I appreciate the packaging advantages / issues, but what I'm struggling to understand is the advantage of not running it as a 50/50 system by default, as per the Torsen cars. As above, on the face of it, you have all of the disadvantages of true 4WD (weight, complexity, fuel consumption) without some of the key advantages of true 4WD / AWD (neutral handling, instantaneous grip, feeling of security and so on).

It clearly works well and is deemed the way to go as virtually all soft-roaders use similar systems, even quite large ones like XC90's and Santa-Fe's.

So, is it a diff down somewhere: my Terracan 4x4: has no centre diff so front axle runs free unless you have very low grip, in which case you avoid torque wind-up via a bit of tyre slip? Or is it that running a true AWD naturally induces losses that a virtually disengaged Haldex doesn't?

I should point out btw, I'd just interested in this as an engineering principle rather than swaying any buying decision :)
 

Jeetesh

Member
I’ve read loads on the default split and yes differs to where you read and application but yes the disengaged Haldex doesn’t have the frictional losses that the permanent torsion based system has.

I’m no engineer but love reading this stuff so my commentary is engineering principles too (just from my understanding). I do however remember when buying my eclass I tried the 4wd as well as the rwd and was a bit surprised at that one. 4wd felt rwd all of the time except when conditions were slippery but there was so much grip In rwd (from front and rear) that it didn’t cause a problem. Unusually the 4wd is slower 0-60 and top speed and that can only be down to frictional losses and weight. 4wd also has a worse turning circle and could not justify it for maybe 3 days benefit per annum (snow) in which snow socks worked a dream or stay at home. I’ll take the 8 mpg advantage instead of the 4wd especially as my tyres are 275’s and 245’s.
 

Rusty911

A2OC Donor
... but yes the disengaged Haldex doesn’t have the frictional losses that the permanent torsion based system has.
Ahh, that makes sense: I guess there is enough of a difference between a loaded system and one that's just coasting to justify losing the permanent AWD advantages.

I think for me, part of the whole TT thing is that it's a little four wheel drive coupe which was just about unique at the time.

As a daily though: ah, well that's different. I had a XC70 for a while, and like you, all I could think about was lugging about all that extra stuff for no real gain. In fact, the main gain was literally as ballast, as the XC had a useful towing limit of 2100KGS rather than the 1800-2000 of the V70. In the end I sold the XC and went V70. (Then baled on that, but that's a different story).

As you say, 0-60 times are often worse, esp if comparing essentially RWD cars as they have enough traction to get off the line effectively anyway (at least until you get up to monstrous power). Clutch life is another one.
 

Jeetesh

Member
Fully agree..... but then who does a race start off the line every time...... maybe the odd bmw driver but definitely not your average e-class driver!
 

ajsellors

A2OC Donor
Any downsides to the software that you've found?
None that is immanently apparent. I haven't had any noticeable trend change in MPG but my use of the car is quite varied so different fill ups produce quite different results. It may end up reducing the tyre wear overall as less wheel spin on the front would mean less wear.
 

Ian Bigg

Member
Having brought a fair few back from europe many moons ago with a friend who was a trader. My choice of TT would be a 180 none 4wd.
Fabulous handling in a great smallISH car.
interior would be the Baseball leather. Loved that so much I bought the seats and fitted them to my smart roadster.
 

PlasticMac

Member
Having brought a fair few back from europe many moons ago with a friend who was a trader. My choice of TT would be a 180 none 4wd.
Fabulous handling in a great smallISH car.
interior would be the Baseball leather. Loved that so much I bought the seats and fitted them to my smart roadster.
Do you mean FWD? Would be (already is), my choice. Lightweight, mechanically simple, Euro 4 etc.
Baseball is a bit like Votex, quite rare. Not so Marmite though.
Mac.
 

Rusty911

A2OC Donor
Baseball looks outrageous in pictures (I've yet to see it 'live'). Utterly concept car.

Amazed they fit in a Roadster!

Ian: Roadster or TT given the choice? I guess the answer is the former if you've got one?

There's what looks like a decent 180 literally just down the road from me, but the seller's all over the place: price has gone up by several hundred, history missing, then not missing. Three lady owners checks out to be six previous. Last belt eleven years / 75k ago and doesn't return calls.

Oddly, it's on its third round of ads. In the trade we always referred to sales prevention officers: I think I might have landed one.
 

sid47

Member
HI I have had a tt roadster for 17years this year Happy Birthday. Bought it new in 2003 used mainly in summer moths. It is only the two wheel drive 150bhp. It is fun to drive, as if it is on rails. Was on the original exhaust till last year. Had no probs still drives like new "no i dont want to sell it". hood is good paint as well never been in a garage. It is now loose will do 0 to 60 in 6 sec. Average full consumption 32MPG. WILL DO OVER 40 ON A LONG TRIP. Good luck.
 

Ian Bigg

Member
The FWD version is what I would have
Yes I have smart roadster and coupe along with a crossblade with ALOT of carbon fibre parts

The baseball leather works really well in the roadster. Very comfortable and great support
 

spike

Well-Known Member
Talking of baseball,
Kevin Bridges once commented on a conversation he had with a sports shop owner down the shady end of Glasgow,
''We sell dozens of baseball bats every week he said ,,,,,,,,,,,,,, but strangely no one ever buys any balls

Cheers Spike
 

Rusty911

A2OC Donor
Actually got round to driving one earlier: just fate that one was literally down the road. A 180 Quattro.

Really liked it: much more than general forum talk (not here) would have you believe. 'Think' I prefer it to the Roadster. Enough to carry on with the search anyway. I liked the 180 as well: had enough go for me and as it runs a smaller turbo with higher comp ratio you'd imagine a fraction more efficient in real life, although official figures don't suggest this particularly. I guess the distinction is pretty moot: neither are frugal. As they are literally nearly double the weight of the Roadster I wouldn't expect otherwise.
 
Top