7–Speed S–Tronic Gearbox

Writing about web page http://www.eurocarblog.com/post/677/the-new-audi-s-tronic-7-speed-gearbox

Today VAG announced they will be launching a 7 speed S-Tronic box suitable for use in longitudinal installations (think A4, A5, A6, A8, Q7), presumably as an alternative to the current Tiptronic offerings. Thinking about this a little, it is not really surprising, given that we’ve had the A5 for over a year now and we still have not seen any models featuring the ZF HP26 gearbox as used in all the other Audi Quattro cars with longitudinal engines. It would appear that VAG intend to replace the ZF box with the S-Tronic, rather than alongside it as the marginal cost of offering both would surely be prohibitive for the number of people in the motoring public who could tell the difference.

I feel however this would be something of a shame, because for a start the ZF HP26 is one of the finest automatic gearboxes you can buy today – its list of clients includes Rolls-Royce, Bentley, Jaguar, Land Rover, Audi, BMW and even Aston Martin. It’s a very smooth box with no perceptible changes whatsoever and fantastically responsive, it’s not even a very thirsty box thanks to lock up in each gear. OK if you are fussy then when you flick a downshift using the paddles then it does take a couple of moments but nothing terrible at all.

If you read (and believe) the motoring press, they will tell you the DSG/S-Tronic box is gods gift to motoring, they’ll spend hours extolling the way that a Golf R32 DSG shifts like lightning as you battle round Brands Hatch and how the GTI is the same but more agile. Clearly what none of them do is what people actually buy automatic cars for – they don’t sit in traffic on the M25 going from 0 – 15 – 0 again in three hundred yards. It is here that one of the DSG boxes least pleasant features becomes obvious, when moving off from rest there is more lag than with a conventional auto as the torque convertor is missing. That’s ok in most circumstances because the newer ones apparently creep at idle (link) now.

The second big issue I have with DSG boxes is the lag when accelerating. DSG works by guessing which gear the driver is going to want next and getting it right more than it gets it wrong. The trouble is when you are coming to a roundabout and want to squeeze into a gap, a DSG car reacts somewhat differently to a conventional auto. In a conventional auto as you apply lots of power to get into the gap, the transmission senses the increased flow and slips the torque convertor long enough to allow the downshift. In a DSG in the same situation (say 2nd gear is active), the transmission will have preselected 3rd already anticipating a nice smooth transition through. When you ask for lots of power from low (coasting) rpm there is a long delay while the gearbox works out that you actually might be better off with 1st. Meanwhile the car has picked up just enough power in 2nd to be accelerating somewhat, so by the time it shifts down to first all you succeed in doing is launching too fast into the gap because you suddenly got way more acceleration. The problem is especially bad with a 2.0TDI because the turbo lag means you accelerate slow slow slow downshift FAST, it is not progressive. This can lead to some really nasty situations as you wait for the gearbox to make up its mind what the heck it wants to do. For me this is the major one because it can be a safety issue though you could argue if your gap is that small you shouldn’t be trying to take it. I would return by saying that you need to be able to respond quickly to maintain a smooth drive too. Note you can confuse a DSG box in the same way with roundabouts and the like on hills… you know motorway junctions, that kind of thing.

Lastly, a DSG just is not as smooth as a ZF box no matter what they say and at the top end when shifting “on the red line”, the DSG holds fractionally too long with the diesel engines because it seems to be set to change at a specific rev that the governor may not necessarily agree with.

Now I really hope that Audi have managed to correct the second issue in particular, because what you don’t want to do when introducing a gearbox to your key model (and rest assured if it’s designed for longitudinal installs that means it will be in the A4) what you don’t want is a series of drivers who avoid your high end models because they aren’t as smooth and predictable as the others. Of course the motoring press will love them, but then they don’t have to live with them every day for the lifetime of the lease.

Christopher Hinds : 20 Mar 2008 00:22 |  Comments (0) |  Report a problem