You can still turn it all the way off, just set it to the lowest setting, which will disable traction control entirely. Note that there's still ABS functionality, including "ice mode". The only way to disable that is to cut the yaw sensor (there's a DIY for it). With it on, the car will understeer when trail braking because the system is applying the rear brakes to try and straighten the car. Long story short, just don't trail brake