Do you like your lowered x? How did you do it?

[X5SND]

Originally Posted by TriX5

The bag is quite rigid and I doubt it changes shape much with a change in pressure. When you remove air from it, it rolls in on itself and thus lowers the car. In effect it works like a piston, not like an expanding balloon.

I know the gas law but that does not explain how it exerts upward force to keep the car from dropping down.

See this article: Riding on Air Air Springs Aren't New - News - Automobile Magazine

[Icer006]

Originally Posted by TriX5

The bag is quite rigid and I doubt it changes shape much with a change in pressure. When you remove air from it, it rolls in on itself and thus lowers the car. In effect it works like a piston, not like an expanding balloon.

I know the gas law but that does not explain how it exerts upward force to keep the car from dropping down.

When I say rigid, I talk in the physics sense. It is NOT a rigid body. You just said yourself, it rolls on itself...and it does so when pressure is minimized.

P=nRT/V, V is constant.

When you change the pressure inside the membrane, the membrane becomes "stiffer," because there are more gas molecules per unit volume (aka pounds per square inch aka psi).

Let me ask you a question, when you inflate your tires, do you increase the volume or the pressure of air inside?

[Icer006]

Originally Posted by X5SND

See this article: Riding on Air Air Springs Aren't New - News - Automobile Magazine

Good link, it speaks in layman terms for those who don't understand the concept of air suspensions.

I should have had this link a long time ago when I was also debating with someone on the Cayenne forum about the its air suspension as well. Same idea, the person thought that the air bladder acted as a piston and not a spring.

[TriX5]

The gas law is true for a given number of molecules. Since you release air from the bags to go down and pump air in to ride higher that would not be the correct formula when you raise or lower the car with the compressor.

When you lower the car V changes because the bag reduces in size where it rolls in around the lower support. Both V and the number of atoms change. My argument was that the Pressure remains the same. The ride height changes because you add or release air.

However, once the ride height is set then you are right. The number of atoms is constant. When the car hits a bump the wheel goes up and the volume of the bag becomes smaller, the pressure in the bag goes up. However, when the car is steady state (for example sitting still) then raising or lowering the car will not appreciably change the pressure in the bags.

So, for the sake of argument, if the total amount of air contained after lowering 20mm would be 5 or 10% less your spring rate would go up by the corresponding amount. I am not sure about this estimate but it should be somewhere around that. I think a 10% increase in spring rate would be hard to sense in the seat of the pants but maybe it is.

[X5SND]

Originally Posted by TriX5

My argument was that the Pressure remains the same. The ride height changes because you add or release air.

BUT, by adding or releasing air to/from a space (ie airbag), you ARE thus changing the pressure. Because you have the weight of the X pushing down on the air spring, the ratio between air in and spring expansion is not linear. IF the spring expanded at a rate equal to your air in, your pressure would then remain constant. Higher Pressure in each corner translates to a higher ride height.

Originally Posted by TriX5

However, when the car is steady state (for example sitting still) then raising or lowering the car will not appreciably change the pressure in the bags.

Wrong, a lower ride height will have a lower pressure in each of the bags.
The overall pressure difference between my lowest and highest ride settings is about 18 psi.

[TriX5]

Whatever you say bro.... Good luck with it.