I have a Carpet Knife 3.1. But I'm sure it's not that the car is tweaked. Because I just set it right before I ran the last time. But the car will only spin to the side when I accelerate hard from a dead stop or slow speed. But drives straight all of the rest of the time. I'm pretty sure the rear wheels are just slipping. But I will check the tweak and everything next time I run. But I'm pretty sure its not that.