Thread: 4 corner airbags ( spring replacement) - anyone running them?

Originally Posted by martnH

So with air springs you can't really change ride height as your will?
It's more for load management?
Cheers

not quite. more PSI at static the bag extends giving you lift. If you hit a speed bump the axle moves up. the piston (lower seat as described earlier) is pushed into the void in the bag. That action decreases the available volume in the bag for the same volume of air, thus increasing PSI. The increase in PSI gives you a firmer rate while the bag is compressed but then equalises as the suspension returns to its static height. the same principle applies wherever you set your initial ride height (within reason). the reverse applies at extension of the bag. clear as mud?

The kits are not exactly height adjustable, in the sense that you have the ability to sit at lower level for highway and then raised for offroad. They have an optimal working height. In the rears this is about a 6cm range (from total height of 23-29cm). I found at the lower end, it tended to have some body roll. So as you approach the upper and lower limits the compromises come into play.

I see it more as a set and forget kind of deal. I do have the option to drop it for hooking up trailers and when I go the fronts to drop the car height to get in the garage. But really I see the only time I would touch the pressures would be when I'm loaded or towing and I add air to level it out.

For me it was, a choice of stock spring rate and helper airbags or this. This I thought had the benefit of a nicer ride like the rear airbag equipped D2s. That was how the D2s run it in the rear. With a D2 it sits at an optimal height, when people lift their car they generally run airbag spacers, not bigger airbags. The rear bags can drop for hooking up a trailer and have a height extension button for when you need it off road (but you are limited to the speed you can use it in), it will also self level when you load up the car. It was essentially this system that I am replicating. The newer D4s have a bit more going on with stability controls etc. I believe, which gives them the height adjustable system they have.


Bit of info from Accuair site

Q: Can I adjust the Spring Rate of my air springs along with the height?
A: Yes, but the Spring Rate will be directly connected with spring height. As you raise the air spring’s height, you will also be increasing the air pressure inside, thus increasing its Spring Rate. Unfortunately, this is opposite from what most of us would want for performance applications, (low and firm for handling, high and soft for mobility). One way to adjust the relationship between Spring Rate and vehicle height is to change the mechanical installed height of the air spring, or make it adjustable. Another way to reduce the spring rate is to add an accumulator tank plumbed in parallel with the air spring (sometimes referred to as a “ping tank”). When you purchase a complete Air Suspension System from AccuAir, you can rest assured that the spring rate and overall ride quality has been optimized for your application. AccuAir and our Industry Partners focus on providing the best possible balance between ride quality, handling characteristics, and ease of installation for your vehicle.

Originally Posted by clintooo

As you raise the air spring’s height, you will also be increasing the air pressure inside, thus increasing its Spring Rate.

This is incorrect. The pressure will change little with height. The pressure is simply the load divided by the area. The load is constant and the area is constant in the working range. As you increase height, the volume increases. With little change in pressure the spring rate DECREASES as you raise the suspension.

For a cylindrical air spring the initial spring rate is pressure (absolute) times area divided by length. As you compress due to axle movement, the volume decreases with travel and the pressure increases at the same rate, causing the spring rate to increase to the square of the remaining bag length during the dynamic loads. The shaped lower seats modify this rate and you need to determine the actual rates from the spring data sheets. Regardless, the rate always increase as you lower the ride height and increases as you add load (requiring more pressure)

Here is the data for the springs in question. W01-358-9327

>> Bushie Suspension Bushie Ute

As you can see, load is constant at a specific pressure within the preferred ride height of 9 to 13". The rates are low (compared to typical coil springs) at the high height and will increase as you drop. You could figure out the approximate numbers from the geometry of the lower seat and the bellows.

Due to my sagged front coil springs I was running the rear bags somewhere between 8 and 9” so the car looked level....I found on my speed test the rear bags would bottom out. Now that I’m running in the range it doesn’t bottom out.

I’m guessing shocks might need to be slightly different for bags??

Hey Pedro!
Can this thread be linked to the Good Oil?

shocks was the big unanswered question. There just doesn't seem to be much out there on what to run with them. Plus airbag man seem to avoid the issue. All I could find was where people were running the Koni raids.

I had the lower bolt freeze halfway on my tjm shock. By the time I pulled out the big impact gun to get it off, it had shredded the thread. I tried to recut it, but it didn't really hold up so I thought bet not to drive it. So car is off the road until new shocks make it across the nullaboar.

I ended up ordering a full set of Koni raids and I also ordered the front airbag kit while it was on sale.

But I will play around with the airbag pressures for the rear and get you an idea of how ride height changes with PSI. Seems my 40psi is a little below the recommended on that bag though.