AusA8

Does anyone have the WABCO part number of the compressor??

s4master1

agree with Mishar on this, you can not compare it with tires even though your version also makes sense, specially in a system like the Allroad uses.
difference is the A8 spring is actually encased in an aluminum housing thus it does not increase in diameter like the Allroad spring or a tire for that matter.
this system is used for a few reasons space been one of them, but also combined with electronic dampening assist it reacts much faster and accurately than an exposed spring.
been encased it can only go up or down.
now as longest load doesn't change all it takes is more air volume to raise as it is a pneumatic ram.
use this example, when lifting a car in a hydraulic hoist the pressure at the beginning starts from 0 and increases until the car leaves the floor, from there on it remains constant no matter how high it gets, so the only thing that changed was the amount of oil.
the tire or the Allroad spring expands to the sides as well.

Edd W

I agree, my analogy was not good because tyre is effectively resisting the force the air is exerting with ever increasing opposite force - until it bursts!
I am still not convinced about the pressure being linear if the mass remains constant. I can understand that in the theoretical world it would be, because there is no increase in opposing force, but in the car, there will be other factors to take into account like resistance of rubber bushes and all the ancillary equipment linked to the unsprung suspension components - brake pipes, ride height sensors etc..... all these will require a reasonable increase in force as they are moved from their natural resting position - OK I am clutching at straws here, I accept I was wrong.

mishar

You are absolutely right!

s4master1

both are right and wrong, am in the middle as didn't read all the facts.
Mishar claim is good and agree as is stated with the car sitting still, weight does not change.
Edd is right as he states the car moving, thus changing weight like on a turn weight shifts more to one side.
both makes sense in a common hydraulic or pneumatic system.
in the A8 however the system is aided with electrical input in the dampers, to minimize body roll/diving or squatting, voltage is applied to the dampers and an internal valve closes or opens accordingly preventing hydraulic fluid flow within the damper keeping it a steady position.
air pressure change is minimal thanks to this.

Mister Bally

415 403 116 0

go to the www.wabco-auto.com website, product catalog INFORM, product number, enter the number I just listed (spaces are important as I listed them), you can click on a very nice engineering drawing.

mishar

We were not discussing car dynamics. I’ve stated that pressure is constant for the constant load and that height is changed by changing volume. Constant load means constant force and it is not constant when car is moving. We can discuss that too.

I don’t think you are right here. Internal valves do not close oil flow completely. They just choke it making shocks stiffer, but not totally rigid. So, by making shock absorbers stiffer we can’t prevent body roll in any longer curve. Roll comes slower but eventually it is there. That’s why we have anti roll bars. There were anti dive systems on some motorcycles that would completely close oil flow in shock absorbers when brake is applied. Not that good idea because totally stiff suspension kills the grip on anything but perfectly flat surface.

There are systems generally called Active Suspension, but as I know they are still experimental. They should prevent any body roll. I’ve seen Volvo lining into the curve like roller coaster, but it was on the test grounds, not on the street.

s4master1

correct. I got confused on what exactly was, standing where there's no weight change and or moving.
my point on the internal valves was to aid on the position during weight change as in a turn, in that case for air to compensate would need a huge amount of air very quick in and out to compensate pressure and dampen the extra load, so is more efficient easier and practical to use flow restricting valves internally in the damper.
there's already system on the road that work faster and easier almost instantly, voltage controlled viscosity. (magnetorheological)
Porsche is using this even in motor mounts in the turbo 911, and is working amazingly.

jakematic

Saw an interesting video on this about the Bose suspension just recently:

<iframe width="425" height="349" src="http://www.youtube.com/embed/Lyf4rfT7bHU" frameborder="0" allowfullscreen></iframe>

AusA8

Thanks Mister Bally. I've managed to track the WABCO distributor here in Aust and I need that number!