I'm using the SpeedCarts, and sure they don't turn the best, but that's why I made the embankments to help you around the corner.
It just seems more like a dirt track with the slight banking, the karts you are using are for asphalt, no suspension or anything. It's an amazing build, but the proper dirt bike would be bitchin' in that circuit ;
I think I remember a good dirt bike that handled well, it had a number plate on the front too, just to match the racing look. I'll try to do some research.