I used acer ceramic bearings, Tamiya may be investigating ceramics for use in the near future
. I blew them out and relubed them with some light oil. They don't need to be blown out because they come prelubed with a oil, not grease, but I did out of habit. Also, the rubber seals on the bearings are a little draggy at first but when you've put a couple of packs through the car, they seem to really free up. Overall, I was pleased with the ceramic bearings...it wasn't like they were faster or anything, they just held up a lot longer with less maintenance. I used mine for six months before I replaced them. Now I'm running the Tamiya blue shield bearings in the axles and Xray high speed bearings on the diff/oneway. It's free but not "blow on the spur to spin up the drivetrain" free.