Greetings Icecats, i've recently came across a post of yours ( increased resistance ); Big Jim Greenemeyer contributed to a great read " Big Jim's RC Motor Black Book " -author Hank Hagquist . If you considered to dwell more into as to why there is more resistance across the commutator , this book may shed more light on your inquiry. You have a good question [ that many rc car people have/had ] .Anyways, good luck with research. -Greg