Okay, I figured it out, but it may not have been the best way of doing this, since karts are really bouncy. But for my purposes, I was right.
Basically, I went into the Vehicle_Speedkart addon and changed two variables:
1. Body Friction
2. Body Resitution
and I made the values higher than what they originally were.
Again, probably not the best way to do it, but it sure does make for some funny moments.
Locking.