I do not know why this is true ... but I've found that if you use a wire
wheel in a dremel and clean the Kadee wheelsets by running them
in an old plastic truck and getting them to be bright shiny - that they
do not pick up dirt as fast as they do with the blackening on them.
We can speculate on the reason - I prefer to just know that it works
and use them with very few problems with dirt build up. As in - I
have used them for 2 or 3 years without any build up ... recleaning
them, when necessary, is as easy as removing them and running
them thru the make shift "dirt lathe".
I agree with you/others that they are not the best - but if you already
have a Kadee car equipped with them - you do not need to replace
them ... just run them thru "the lathe of heaven" (apologies to Ursula).
- Jim B.