Last week I redid my differentials on my car. The rear one was bone dry. I don't have any traxxas oil here so I used Tri Flow in the rear end. Its really light oil. The front differential had thick oil in it yet but I added a little Tri Flow to it as well. I have noticed that the car doesn't want the back end to spin out as bad anymore. I'm guessing the thicker the oil the more it locks up the differential. I would think you would want the front end locked up more than the back end. I really notice a difference it is night and day !!! I see on the funny cars they are locking up the differential which is the opposite as what the XO-1 would want. When I have my car in the air I hold one tire give it some throttle and when I let go of a rear tire it takes a while to catch back up to the other tire. When I hold a front tire and let it go it takes right off. With the thicker oil in the rear end it makes it have more of a posi traction in the back which would make it more prone to spin outs. With the lighter oil its less opt to spin both tires at the same time and lets it have just enough time for the other tire to grab when the other tire is spinning. Does this make sense to you guys ?? Like I said I notice the difference night and day !!!