JX53mb good stuff as always.
To avoid those darker spots on your model, if I may, you should take a look at the geometry in those spots.
I don’t know how you modeled it, it looks like you went for surface modeling, but usually those glitches, in my experience, are caused by messed up geometry like overlapping vertex/polygons/faces, you may want to check normals too.
I prefer to model with 3DSMAX Mesh/Poly Edit instead of surfaces or curves because I find it easier, but that should be it.
I took a look at you project, great stuff, I have a couple questions:
I quickly tested your vehicle on a track I usually use as a test but it stumbles here and there into the geometry of the track, itself, I might try a higher polycount model to avoid that, does it work only with mesh spline objects?
Is the project fully set up to support network replication and client, server communication? I super quickly looked into and just migrated the vehicle for a quick test.
Now that you are experimenting with motorcycles are you done with vehicles?
Can yours be used for other projects?