Air bags up or down when parked/stored.

[davidbrady]

Hi William,

I'm a fan of keeping the system pressurized and at ride height. That's good dry air you have in there with a low dew point which helps eliminate any condensation forming inside the system as ambient temperatures swing. Also, buses of our vintage tend to use auxiliary tanks, ping tanks, at each air spring. This system lowers the suspension's resonant frequency which is a fancy way of saying we have a softer spring rate and a plusher ride, but if you make it too soft the suspension can bottom. What Prevost did was to include a conical rubber bump stop within the air spring. The bump stop adds to the spring stiffness at the end of the suspension travel. I know I don't want my conical bump stops permanently flattened by prolonged resting of the bus onto them. And thirdly, I've been told the same effect isn't good for our IFS bushings. These bushings shear as the suspension articulates. They're designed to operate over an angle of rotation. It's anecdotal, but a mechanic tells me he sees more suspension bushing failures with owners who store their suspension dumped. You can imagine brand new fresh bushings might not care, but as they age they might. That's my swing at it. What do others think?

Attached is a load diagram for my spring. See how the spring rate is a plush 650 lbs/in but it then escalates to 1800 lbs/in thanks to the conical bump stop: