The traction control reduces the engine power when the slip reaches a certain value.
This value and also the slip values versus velocity can be set in the TC EDIT page on the slip/velocity graph.
Also you can choose to play with one of four presented options: 0%, 100% and pre-set value.
Choose 0% if you want to have no traction control assistance, 100% to have slip ratios at minimum values (full Traction Control assistance) or a pre-set value to play with your own setting for the slip ratios values.