This for sure, the whole point of the 0 density function of A-Chassis is to make parts weightless so your body parts/meshes don’t affect the weight of your car, and in games that don’t utilize fluid forces, parts floating isn’t exactly going to be a concern (at least that’s what i can understand with parts being lighter than air causing them to float, since if there’s no forces at all that shouldn’t happen, right?). I’d like to be able to test the waters with this change to see if it’s even worth my time to start changing hundreds of initialize scripts to be compatible with the new limits, since right now all we know is that it will happen, how it will affect things in theory, but not how it will actually affect our things, since we can’t test it for ourselves beforehand.
Setting the density to 0 does not actually set the density to zero, it gets clamped to 0.01 today, so parts are not weightless. You can set the Massless property to true, which, under specific conditions, prevents parts from contributing to assembly mass. However, Massless is independent of the density, and is ignored when the part is its own root part.
If you want to set the density of a part to something very low, but future proof it against changes to the density lower bound, we suggest setting the density to something at or above the lower bound, currently 0.01, and soon 0.0001, rather than setting the density to zero and relying on clamping behind the scenes. That way any tuning you do that is affected by part mass will be insensitive to future changes in the clamping.
Most of the A-Chassis base code was written somewhere around 2017 or so, back when Massless wasn’t a property yet, that is why 0 density was opted for, regardless on if it was truly 0 or not, there are external scripts that enable massless for all parts, however i am unsure if a functionality like such was ever included inside the actual Initialize script, still, the ability to be able to gauge what kind of an impact this update will have on our stuff (especially since A-Chassis is heavily used inside of “slot” communities that likely don’t know anything about this change (or how to edit their existing a-chassis installations to not be affected)) would be greatly appreciated, since this will have a massive impact on things, and given that, an opt-in preview be (likely as a beta feature) would be of huge help, not just for developers that use it, but also for the car community as a whole.
this update sounds super cool, cant wait to try it out
We will update this once the change is live 
wow i can’t wait to play physics, maybe we could create hot air baloon? if possible, can’t wait 
Is this change still going live today? I just checked, it’s still not happening yet.
Hi Everyone,
Due to too many experiences still clamping the minimum density of parts incorrectly, we will release this change through a 3-phase rollout workspace property. We plan on enabling opt-in for this feature by End of March.
Also, to assist with this incorrect clamping, we have added a warning message in Studio for any experience that clamps any Physical Properties to their minimum or maximum values. This warning message should help you know which script(s) are doing this and need to be adjusted.
Thanks,
M0bsterLobster
Please refer to the update - I apologize for the delay. We had hoped a 3 phase rollout wouldn’t be necessary.
Is there anyway to opt-in early?
The physics based experience I’m making requires the density of then part to be lower than it current minimum of 0.01 for it to work as I want it to…
Does this change also add a maximum density? Previously we were using density on some cars to help give them some extra mass, but now I’m seeing warnings about 100 being the max density. I don’t think we’ve made any changes to our cars but I started seeing this about a week ago.
Hey @CompilerError,
Thanks for the feedback. We have not modified any of the density bounds yet and at this time we are only looking to lower the minimum bound. The warning message we recently added is just checking against the current bounds (see PhysicalProperties | Documentation - Roblox Creator Hub) and printing out if any of the physical properties (including density) are clamped. I would not expect to see any behavior changes from your cars as the message is not a functional change - just a warning that the density you’ve been getting is not what you’re setting. Hope that helps
Hi
Could you please add a stacktrace to the output warning. It’s hard to track where it comes from, even with the suggested find-all trick.
Hi Apenz1,
Thank you for the feedback. We initially decided not to add a full stack trace to the output warning because it could potentially be a lot of output without the ability to collapse it.
For this reason, we did add the ability to click on the warning and have it take you to the script which is causing the issue and the ability to hover over the warning and have it tell you the path to the script.
Is there a use case we didn’t account for that requires the full stack trace?
Best,
M0bsterLobster
I only see the warn in the error analytics (real game errors). I can’t seem to reproduce it from testing in studio.
Thanks for this. I can reproduce the issue you mentioned on our end and we are currently investigating solutions.
Hi Apenz1,
Thank you for pointing out that oversight - you should see the fix (provide script and line number in error analytics) in 2 weeks or so
Best,
M0bsterLobster
I’d like to point out that for any games that heavily rely on A-Chassis, If you’re in need of a quick fix to get your game playable while making further changes then you can set the “Tune.CustomSuspensionDensity” in all the A-Chassis Tune modules in your game to the updated amount & fix the broken suspension problems.
I have been thinking about writing my own post regarding the A-Chassis bug (as I have figured how to fix this issue on my own) for a day or two but I see someone was quicker. Thank you, @m0bsterlobster, for bringing this up. I bet many creators will thank you 