Bag over coils performance

[Oh Damn, it's Sam]

Depending on the spring rate you desire, you might be able to reach it with air bags. I can offer you the equation I use to calculate instantaneous spring rate for air bags if you want, but it does require some math.

Otherwise, if you're looking for an extremely stiff setup, I don't think you're going to be able to achieve it with air bags. You can get pretty stiff depending on how much uptravel you require at ride height, but you're not going to see much beyond 1000 lb/in with any setup I can envision.

[Legoctf]

So I could still get a desired spring rate if I got the right bag setup correct?

Honestly up until very recently I would never have consider bags over my coilovers, but as I have been seeing, bags can be performance oriented and thats why they are attractive to me, especially the bag overs since I already have good dampers

[Oh Damn, it's Sam]

Gotcha. In that case, unless you drive with the bags at full extension (which you probably shouldn't), you actually won't have control over the pressure inside the bags. You see, the pressure inside the bag is a function of the weight of the vehicle and the dimensions of the bags themselves. At any point between slammed and maximum height, adding more air to the bags won't increase the pressure - instead, the vehicle will rise and the pressure will remain stable until the bag reaches maximum extension, at which point the vehicle will stop rising and the pressure in the bags will increase. It sounds counterintuitive, but that's the principle.

In fact, all other things being equal, what controls the instantaneous spring rate of an air bag is actually the ratio between the fully-compressed height of the bag and the height of the bag when the vehicle is at ride height. The closer to fully-collapsed the bag is at ride height, the higher the effective spring rate will be. Unfortunately, this means that the stiffer the spring you need, the less uptravel you wind up with.

Do keep in mind, however, that air springs are naturally progressive: the more they're compressed from ride height, the stiffer they get. You may find you do not need nearly as stiff an airbag as you would a comparable linear spring.

[Legoctf]

No no lol, I mean replacing my springs on my stances with a set of universal air aero sport bags(or at least that style)

So the bag will go directly around my damper replacing the spring in the coilover

[Oh Damn, it's Sam]

If I understand correctly, you're planning on what the VIP guys call a "cup kit," where a small air cup sits above the spring on the coilover, allowing the vehicle to be raised an inch or two when desired, correct?

Depending on PSI, the air cups will have a given instantaneous spring rate, but if my understanding of the physics is correct, you will only be able to subtract from the rate of your coil springs.

[Legoctf]

So I have an evo x currently on stance ss+ coilovers and recently have been looking into bag over coil setups using my stance dampers.

My main concern is I dont want to kill the performance handeling of my evo by switching over to bags, but my understanding is that depending on the psi you run in the bags it effectively creates a spring rate. So theoretically I could create a 10k 8k spring rate setup correct?

Are they any downsides to this style of setup both for performance and lowering wise?
I believe the accuair s4 runs this style setup which was what made me look into this.

Any thoughts or things im overlooking would be greatly appreciated, thank you!