I've been very happy with the combination of 100k front diff and 30k rear diff. My times at my track are getting more consistent every week. I shimmed the transmission on the front pulley of the car and it rolls a whole lot smoother. Other changes that I made are side belt = Mugen, front belt = kawahara low friction belt, and the rear belt = Kyosho Sp belt. The brando belts are less then desired. Hope to have a successful outing. Thanks for all the information posted so far, this is a great reference tool.