Increase touch target size of UISlider with Swift

Subclass UISlider and in your custom class of slider add this method,

  func pointInside(_ point: CGPoint, withEvent event: UIEvent?) -> Bool {
    var bounds: CGRect = self.bounds
    bounds = CGRectInset(bounds, -10, -15)
    return CGRectContainsPoint(bounds, point)
}

Then create object of that subclass when you used slider.

If you have used slider in interfacebuilder (storyboard) then set it's class to that custom slider class from identity inspector.

Swift 3 update of Lion's great answer:

import UIKit

class CustomSlider: UISlider {

     override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        var bounds: CGRect = self.bounds
        bounds = bounds.insetBy(dx: -10, dy: -15)
        return bounds.contains(point)
     }
}