Physically the steering wheel will fit but the airbag on the B8 went back to single stage in 2012 when the B8 became the B8.5 so the airbag will not be the correct one for the airbag system.
The wiring can be adapted for the single stage airbag from the B8.5 but not only is this dangerous there is also no way to know if the airbag will operate properly until it’s too late.
In order to get the desired effect of having a flat bottom wheel with a correct 2 stage round airbag and correct MFSW buttons then the Mk2 TT is the only one which ticks all the boxes. That is the wheel pictured.
This is based on a lot of research of different wheel and car combinations.
Like I said, you can fit a different airbag and adapt the wiring but with the risk to life it’s not worth it just to have a nice looking wheel?
Here is a pic of the Mk2 TT round airbag for the Flat bottom steering wheel showing the 2 igniters for the 2 stage airbag system.
In your pics, you can see that the round airbag only has 1 igniter port so would need wiring modification to be plugged in to the car. No way of knowing if it’ll work though lol.
It’s well known about the airbag issue, just most people choose to ignore it and fit the wrong one anyway and drive around with a question mark explosive in front of their face ha ha. Oh, and with buttons that have ones that will never work due to different infotainment systems.
For me personally, unless it can be retrofitted to be 100% as factory then it’s not a proper job lol.
Anyway, I just wanted you to be fully informed before makeup by a decision but you’ve already solved your issue so I guess you can never know too much
I think you are wrong, and I will try to explain why.
A good source to find out how the airbag system works in different Audi models is the Self Study Programme (SSP). Audi has released such programmes for a lot of their cars and their components.
Let's first have a look at Audi SSP 409 - A4 2008, page 11-12:
"All Audi A4 '08 models distributed world-wide are equipped as standard with an adaptive driver airbag. This is a single-stage solid fuel generator with an additional igniter for adaptivity. The airbag control unit J234 activates igniter 1, thereby in turn igniting the ignition charge. The actual propellant charge is subsequently ignited via nozzle ports. When the gas pressure produced by combustion of the propellant charge exceeds a predetermined value, the gas generator housing changes shape, thereby providing a clear path to the airbag via the inner housing and the metal filter. The airbag unfolds and is inflated.
An additional igniter - driver side airbag igniter -2- N250 - is located on the back of the airbag outside the gas generator. A cord which seals an additional discharge port is wound around this igniter. The discharge port is kept sealed as long as the cord is held in place by the igniter.
Depending on the severity of the accident and the driver's seat position, the airbag control unit J234 activates the igniter 2. The igniter housing ruptures and the cord is released. The volume of the airbag increases by approx. 4 litres, and the additional discharge port is opened. This discharge port allows more gas to escape from the airbag. The airbag is "adapted" to suit the occupants."
As we can see, the Audi A4 B8 series has a single stage airbag with an additional igniter.
Since you mention the TT mk2 wheel, let's have a look at Audi SSP 380 - TT coupé 2007, page 12:
The Audi TT Coupé ‘07 has two-stage front airbags on the driver and front passenger sides. The airbag control unit selects the time interval between the two ignition stages (approx. 5 ms to 30 ms) according to severity and type of crash. The loads acting on the driver or front passenger during an accident can be reduced through time-staggered ignition of the propellant charges. Both propellant charges are always ignited. This ensures that no propellant charge remains active after the airbag is deployed.
A gas generator with two pyrotechnic propellant charges is integrated in the driver's airbag. Igniter I is activated electrically by the airbag control unit J234. The igniter flame passes through the container and ignites the ignition charge in the container. If the pressure produced by the ignition of the ignition charge is high enough, the flame will break through the container and reach the propellant charge through the perforated tube. Propellant charge I ignites and combusts. The developing gas destroys the foil seal, and filtered gas flows through the air outlet into the airbag. After a defined interval has expired, the airbag control unit activates igniter II, which in turn ignites propellant charge II directly. The gas produced by combustion of the propellant material flows through the raised end cap into the combustion chamber of propellant charge I. From here the gas flows through the filter into the airbag.
The Audi TT mk2 has a dual stage airbag system. This is also true for the Audi A3 8P (SSP 332, pg. 16).
How I understand the above information (disclaimer; I am not an Audi tech!)
- Single stage airbags have an additional igniter to increase airbag volume and help gas escape from the airbag for faster deflation, depending on driver seat position and severity of the crash?
- Dual stage airbags have two igniters which always ignite within a pre-determined time delay, and activation of the second stage keeps the airbag inflated for a longer time period?
Conclusion:
The Audi TT mk2 airbag is not suitable for the A4 B8 series. Looking at pictures, the facelifted B8.5 round airbag is also a single stage airbag with an additional igniter (similar design). But there's some differences in the slip ring connector compared to the early B8's. I don't know for sure if the round airbag facelift steering wheel is a safe retrofit, but it seems like a pretty common mod on various german forums...
Untitled by craig hill, on Flickr
Untitled by craig hill, on Flickr
Untitled by craig hill, on Flickr
Untitled by craig hill, on Flickr
