vtraudt

Hackers to the rescue!!

I am sure there is quite a bit of potential in our suspension system still to be uncovered.

Next time on the hoist, I will also check if there is a mechanical way to preload the airbags (higher pressure, stiffer spring rate).

Does someone have contacts at Arnott/Bilstein to find out more about the spring rate of the stock/Gen 1/Gen 2 bags, and the dampening rates of the stock vs. Bilstein shocks?

How about a supplier coming up with electromagnetic shocks for the Allroad?

JustMtnB44

Don't you have Gen II air springs already? These are 30% stiffer spring rate than OEM air springs. The lower aluminum piston is much larger than stock which is why they get stiffer when lowered, and the aluminum sleeve on the outside does not allow the rubber air bag to flex outward as much which keeps the volume more consistent. Your concept of reducing volume to increase spring rate is correct, but putting liquid in the bag is a bad idea IMO because the chance of it getting into the air supply lines during level changing and damaging the valve block is too great.

I haven't tried this yet, but mostly because I don't see how it could possibly work. The only thing that can be changed in the suspension is how much air is pumped in to or let out of the air spring. The PDC valve is only actuated by air, there are no other connections going to it. So it directly relates air pressure in the air spring to air pressure inside the shock. The pressure in the spring is determined by the load on that corner of the car. It takes a certain pressure in the air spring to maintain a certain ride height level (as measured by the level sensors). So when you load up the back of the car with additional weight, the system adds air pressure to maintain the same ride height as before, which also increases the pressure in the shock to modify the damping. If the system were to add air pressure without additional load on the car, then the car would just raise up.

The lack of this valve is why I wouldn't use Bilstein rear shocks on my car.

I don't think the pressure changes all that much from one level to another. The air volume does change some, and the amount of air changes, but the pressure to support a given corner weight of the car is closer to constant than widely variable. So the PDC valve shouldn't be changing the damping all that much from one level to another. It is after all only designed to change the damping for increased loads, which will increase the static pressure for a given ride height.

I don't think it was ever confirmed the trailer towing input does anything other than disable the parking sensors, but if there is something please post a link. The trailer weight is only seen as extra load, and the suspension will add more pressure to the rear air springs to keep the ride height constant.

I asked Arnott a few months ago for a graph of the Gen II spring rate. They said they didn't have one, but told me the Gen II springs are 30% stiffer than Gen I or OEM in all level settings.

I would love to have active damping shocks on the allroad! I've thought about looking into it, but unsure if any manufacturers work in low volume, and then it would probably be very expensive.

vtraudt

JustMtnB44: all checks on what you stated.

The only way to stiffen the air springs would be to 'fake' higher load (adding salt bags is NOT what I mean), which increases the required pressure for a given height, and consequently a higher spring rate (see graphs in earlier post). The mental picture would be 'rubber bands' around the top/bottom of the bags/suspension parts. Or a 'helper spring' (that pulls the top and bottom together). Neither of those solutions seem practical.

Aside from fluid, an 'insert' would also reduced volume (reduced volume = increased spring rate), but even less practical (Arnott went that way by making he 'piston' larger (= more displacement volume for given travel).

If the Arnott springs are 30% stiffer, the shocks (I'd say at least the rebound rate) should have 30% more dampening as well.

Pretty sure this explains the 'bounce' I currently experience (underdampened front from combination higher spring rate with stock rebound rate).

If the Bilstein Arnott shocks are not 'custom' made for Arnott: has someone seen information on the Bilstein shocks elsewhere?

JustMtnB44

Are the Arnott Gen II springs not stiff enough for you? Personally I can't imagine having any stiffer springs up front, as on the really bumpy roads we have around here the ride quality is already poor. I think what would be more important is increased damping in both compression and rebound, which would give a firmer feel and reduce bouncing. Traditional suspension setup is always a compromise though.

We need these shocks as an option.
http://www.activeshock.com/

Kristopher

You could possibly increase your damping in the rear by modding that PDC valve throttle. If you could decrease flow through the PDC it'd increase the rear damping.

I found another explanation for the PDC which helped me.
http://www.dynarev.com/Audi_fuel_exhaust.html


...I learn something new every day

vtraudt

They are certainly not TOO stiff for me. Until I have seen/felt 'too stiff', I can't really say.


Yup. My desire for 'firmer' may actually come from 'not enough dampening'!