I know its an old thread but I was so surprised by the handling and ride comfort differences after comparing 3 and Y for a week that I just had to share this experience. Not what I expected!
Have driven Y LR 7 on standard 19" wheels as mostly my daily for about a year and 22k miles. Have hade 3 LR on standard 18" as a loaner for a week now.
These are my My 3 vs Y observations as it relates to this thread:
Handling:
3 wins hands down, no contest. Flat and balanced through fast corners. When the tires start to slide, it feels like you are still in full control and can modulate things as you please. Tires feel like they are allowed to do their best job, straight and compliant, even through bouncy corners. The 3 seems to effectively dampen any mid corner bumps, at least on the roads where I have driven.
The Y on the other hand feels like it is running up on the outer edges of the outside tires in tight fast corners if there are undulations. Looking at my tires seem to confirm this, since the outer edges are pretty worn out. Y self reinforces bump initiated back and forth pitching, causing the front and rear axles to take turns in giving up and gaining grip through turns, creating little side jumps, one axle at a time. Not confidence inspiring. The Y does however stay planted with very good lateral grip through smooth curves, as long as you keep the go pedal input constant. It comes into its own on flat on ramps and clover leaves.
Interior: Y has a more room than 3 in all directions, obviously
Noise: Y has less road noise than 3, but 3 has a little less boom noise when the rear wheels hit potholes.
Ride Comfort: On smooth roads it feels like the Y is a little better. It's like a cloud on the highway. Over higher/deeper bumps the 3 is instead better. We have a lot of brick streets around here with a constant stream of seriously big bumps. The 3, while making crashing and booming sounds, stays pretty level over those. The Y on the other hand gets into a self reinforcing pitching bounce that is so unbearable that you almost have to slow down to a standstill. Additionally, Y seems to have much more roll stiffness than the 3, creating a strong side to side rocking motion over potholes or if you try to cheat a speed bump by taking it with one side only. Not to mention if you make the mistake of taking one of those yellow parking lot sausages on a slight diagonal -you are in for some serious head toss! Almost no head toss in the 3 under those same conditions.
That said, I am happy with the car. Super practical and still drives a lot better than any ICE Suv.
To sum it up, I no longer think of 3 and Y as two bodies on the same skateboard. They are much more different than that. For anyone trying to decide between them, I would recommend test driving both to compare.
PS. Here is a hypothesis for how the two cars turned out so different: Tesla designed the suspension with the 3 and got it optimal for that car. They later designed the Y and reused the parts for maximum commonality (albeit with some pieces beefed up?). The higher COG and bigger wheels may not match the geometry and measurements that were optimized for the 3. Some Y variants may get more unbalanced than others. Imagine for example if the camber is a mean between the desired values for Performance and LR and if the variant geometries only differ in spring length, the LR with the extra ride height would get less than desired camber, further exacerbating the longer wheel radius leverage compared to a M3, if that’s where the original geometry came from. If the 7 seater just has stiffer springs but common dampers from 5 seater, it can contribute even more to the bounciness. Just guessing, but that’s what it feels like on my car. My hypothesis as a layman. Am I right? Out of curiosity I would like to hear if there are any knowledgeable people out there who can chime in or correct the hypothesis.