https://developer.roblox.com/articles/building-carkit-1
Following that article, I took the time to fully finish the kit. I was successful in doing so.
Now jumping to my issue. I decided to do this again, this time I resized the wheels and the vehicle base. And positioned the wheels accordingly to where they will properly sit on the vehicle.
When it was all said and done, the drive is harsh and isn’t smooth at all, and very unresponsive.
My first guess was constraint issues to match the new sizes, but after countless hours of playing with the various different settings, nothing worked.
Hoping someone with more knowledge of the various different constraints can take a look at this for me. Attached is the file for the exact model I’m using.
CarKit[Undone].rbxm (11.7 KB)
BONUS GIFT - Anybody else who is using this Car Kit, but isn’t good with scripting can take the model and put it with their functioning kits. Since inside I basically changed the script to allow you to group the vehicle together. If you do this, make sure to move the vehicle seat parent from the base to the model.
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I think that this should be in #learning-resources:community-tutorials-resources. Ask a Top Lead Contributor to move this for you.
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It appears that way, however, the main topic is me looking for help in fixing the car. I just so happened to add a little extra.
The wheel mounts are clipping with the body and the wheels. Setting them to CanCollide = false fixes the issue. An alternative is to edit the position of the mounts and wheels and their attachments to avoid clipping. This second method would alter your suspension geometry, and my example below exaggerates some flaws.
carkat.rbxm (12.7 KB)
Maybe because you need to make the car a bit smaller, maybe? I can’t view the video on my bad laptop. Just, make sure the car is a considerate size, not too big or too small. 
So, interestingly enough, I have collision groups set up. Where the vehicle and the wheels + mounts are on two separate groups, making them unable to collide.
Plus, on both Karts you put, the issue remains the same. Where the wheels are just unstable.
I just built the car kit (after having to manually download the videos) and the instability is present even with what Roblox provides. It’s a case of bad design that I should’ve explained. The issue is how the hinge is placed.
Essentially, since the wheel pivots two studs away from its center, every time you go foward the wheel acts as a lever and the hinge is compensating, resulting in that awful wobble. My hopefully final model fixes this as the wheel mount is now inside the wheel. There is now zero wheel scrub.
fixedkit.rbxm (11.5 KB)
