, , Anadin, thank you very very much for your helps. We finally got rid of that problem.
Anadin has sent a fbx file that shows the correct way to rotate root bone. We have applied same solution to our model from scratch and it worked. Before exporting the model to Unreal, we gotta rotate root bone in x axis -90 degree. But wheel bones should be the same value with world’s coordinate’s axis values.
But I must say that it’s really really weird and newbies like us cannot handle with that easily. We have tried every other possibilities by rotating wheels or rotating car completely. I couldn’t understand why root bone should have a different axis setup than world’s axis.
My final worlds, I’m deeply appreciated for your helps. Thank you 