Body parts' effects on changing Center of Gravity

to my knowledge nothing changes the actual weight of the vehicle, just the center of mass. I will defer to someone who more knowledge on the matter tho

The actual weight of the car doesnt matter for handling if i remember correctly, only for crashing.

Ok despite the explicit title mentioning ΔCG, I might have confused you guys in my posting. When I said increase/decrease mass I meant, CG moving toward/away that part of vehicle... People still think there are people who think we can change the curb weight?

Ah hello Tears, fancy seeing you here.

If you've read this part in my document there might be some bad phrasing in there, but there's also this image with the info text:



And a snippet from the bumpers section, regarding front bumper specificly:

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So to answer your questions...

1. For the majority of parts beyond bumpers & parts with collider meshes, only very specific parts still impact the CoM (or CG, as you refer to it, just to be clear we're talking about the same thing). The list of car-specific modifications will be far too long to post here so I'll give the general rule of thumb instead: bumpers & skirts do not impact CoM for the majority of cars. Exception to the rule known so far are neons & rollcage, with each neon tube pulling the CoM towards itself & the bounding volume of the rollcage determining its centre before pulling CoM towards it.

To elaborate on bumpers & skirts specificly their effect is dependant on speed. It should be pointed out that, from me recently toying with my steering sensitivity through Steam, I'm less sure if these parts really change weight/downforce. As the speed increases you get the sensation that the car becomes more and more "on rails". This can happen from simply making the peak slip angle lower (the sideways angle required to hit max grip). The bumpers & skirts will "tighten" the grip of the opposite wheel pair, meaning the front bumper will tighten the rear grip and vice versa. Skirts affect all wheels more or less equally. I've been slacking with updating my document and I apologize for that.

Cars to keep an eye on here are usually muscle cars as the rollcage can add a fuel tank (or whatever that is) to the trunk, causing a massive CoM shift towards the rear. The Dukes is a great example of this. Most cars have the cage centered enough where it might not matter though, but worth keeping in mind.

2. So to clarify "the rule" I referred to above, I'm talking about what I described for the Brawler example. If a part has its own collider mesh (aka. hitbox) and is linked up to activate it (refer to the carcols file of each update to know which parts are used). The logic behind this is very simple: what's the relative size difference (bounding volume) and location difference? Average the CoM location based on these conditions, where tiny parts influence the CoM less. If there is no collider mesh the part most likely isnt affecting CoM.

The 190Z is a very interesting car to look at for this. Stock bumpers and the first few options dont add anything to the car until you either see the massive front wing being added or the rear bumper having those centre-ish blocks added. However the bumper delete options also activate these rather large colliders for some reason, dunno what the dev was thinking there.

3. Refer back to point 2. If there's no collider associated with said part it's most likely only cosmetic, known exception for rollcages.

4. Hm... this got me thinking and I decided to double check.

Nah, the wheel covers are only cosmetic. As far as the physics are concerned the Hermes doesnt seem to have any parts influencing the handling beyond the usual stuff.

Removing parts can indeed have an effect on CoM, like the Coquette Classic's roof, resulting in the opposite of adding parts; centering the CoM some amount for each removed part. Crashing the car and losing parts that way does not have any effect to my knowledge, as the detached part is actually a duplicate and the original is reset & turned invisible.

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Lengthy post from me yet again, but hopefully this answers your questions. As always if you got any more questions ask away.