Adding MR52-2Z / MR52-ZZ ball bearings to LEGO train wheels to reduce rolling resistance of my LEGO MOC trains. I also used DIN 913 M5x10 grub screws to fix the ball bearings inside a standard LEGO train wheel holder (part number 2878) … a method invented by Maciej Drwiega and Pepe Nietnagel.
I bought the ball bearings and the crub screws on aliexpress.com
The video „LEGO Train Wheels with Ball Bearings / LEGO Eisenbahnräder mit Kugellager“ shows how to implement ballbearings in LEGO train vheels.