this is likely since he only sees the issue at quite high speeds.
what...? What is a nut space and 20 pieces of what? I'm confused. Show pics pls
https://cdn1.bigcommerce.com/server4200/i6hhse/products/86/images/298/machined_spacers__14455.1382745602.1280.1280.jpg?c=2
Something like this, my stock 318ci lug nut is M12, while the wheels itself is M14, i have to custom a lug nut spacer just to make sure the lug nut fit in the holes completely. Those spacers actually eliminated 90% of the vibration issue but my mechanic pre-amped me the tyres are too far out, almost stick out of the fender, so i will definitely feel some vibrations.