I looked far and wide for a small (2-wide track) wheel for popular smaller train sets, and couldn't find any good ones, so I created one that fits the bill.

This is not for the larger sets; it's for the smaller 2-bump wide ones. 

I've also uploaded an extensive set of tracks that are compatible with the smaller sets:

[https://makerworld.com/en/models/1583655-tracks-for-small-brick-compatible-train#profileId-1667050](https://makerworld.com/en/models/1583655-tracks-for-small-brick-compatible-train#profileId-1667050)