Hey, I've made a semi fixed Miami Grand Prix Circuit. This my first time making a map so expect some bugs.
It's quite easy to do yourself. All you have to do is navigate the main.materials.json file in the folder where the .dae for the track is located, then scroll down to the material and right before translucentBlendOp put groundType:"GRASS" or groundType:"SAND"
It really is. The whole process takes like 30 seconds for one material if you know what you're doing.