Around where I live there's these soapbox/gravity kart races (google "carros de rolamentos") in which the wheels are built simply from ball bearings. As I was building my own, I began wondering how I could easily mount my large bearings onto my kart, and it occurred to me that an easy way to do it would be to get some smaller bearings inside the ones previously mentioned and mount the resulting pair onto the frame, like this:
More importantly, I was under the impression that this would improve the performance of the kart in terms of speed. I am not completely sure though, hence why I am asking this question.
On one hand, I find that my older kart reaches some sort of terminal velocity when the inner and outer races of the bearings can only move so fast in relation to each other. So, the inner bearing would sort of take some load out of the larger one by rotating in the same direction, allowing the outer-outer race to rotate faster in relation to the inner-inner race (or, in the worst case scenario, I would get no gain but also no loss, unless the smaller bearing spins backwards).
On the other hand, I asked this to a student of mechanical engineering and he said he doubted I would get any gain, because there would be more overall friction, which does make some sense, but does not convince me much.
We can assume that they will be well coupled together (I can file them if needed and will probably weld them afterwards).
I can't run any practical tests at the moment because I haven't bought the smaller bearings yet (I don't know if it's worth it)
From my research, this kind of configuration has only been mentioned in some videos about fidget spinners, and sure enough, it seems to rotate fairly well.