I know this has been discussed in the forum before, but based on my searches it hasn't quite been resolved, it seems. I've managed to import some straights that are very smooth to drive on. Put one after the other and you won't even notice crossing from one to the next, even at very high speeds. I even imported them using the LL importer/physics options, and they still work.
Corners are a different story, they are jumpy no matter what. Just how jumpy seems to depend on lag. Having finally figured out how to get a straight road texture to follow a mesh curve, getting said mesh texture ready and align friendly and getting the curves down to 2-4 LI (sides vs. not), whether convex hull or prim, my curves still might make you fly off the track. Even a simple structure like this.
(Blender is a steep learning curve for me. Even the above "sectioning" took a lot of time).
I've tried importing a very simplified version along with it as a physics model, but it remains jumpy. Any tips or pointers to relevant tutorials (there are tons of tutorials, but not directly relevant to this that I've found) would be appreciated. I've probably skipped a lot of steps here,.