bigger UISlider ok but tracking zone problem

My goal is to create a bigger UISlider with 35 pixels height for the thumb image. I subclassed UISlider and added the method : ``` - (CGRect)trackRectForBounds:(CGRect)bounds { return CGRectMake(bounds.origin.x, bounds.origin.y, self.bounds.size.width, 50); } ``` Then I set the thum image from my controller using setThumbImage: My bigger thumb is well displayed. The problem I have is that the tracking zone is still the same around 19 px height, how to extend it to 50 ? Thanks T.