I would just like to put my hand up as someone who is in exactly the same boat. It seems physics driven bicycles/motorcycles are inherently going to be a problem with the limited choice of collision primitives.
And I agree- a boolean type system, where you could chop out the sides of a sphere with a couple boxes on each side, would do the trick!
My only advice here if you are not C++ proficient (as I’m not), is to maybe employ the help of an AI assistant, such as Claude AI, which I used recently to help me to develop a C++ plugin, which worked very well. I will probably go down this path soon to see what I can do, because the custom or generated mesh options don’t seem to be working out too well so far.
Cheers!