https://www.motorclubamerica.org/files/theme/scroll-fixed-nav_1446856462.js

1jQuery.noConflict();
2	
3	jQuery(function() {
4 
5		// grab the initial top offset of the navigation 
6		var sticky_navigation_offset_top = jQuery('#site-navigation').offset().top;
7		 
8		// our function that decides weather the navigation bar should have "fixed" css position or not.
9		var sticky_navigation = function(){
10			var scroll_top = jQuery(window).scrollTop(); // our current vertical position from the top
11			 
12			// if we've scrolled more than the navigation, change its position to fixed to stick to top,
13			// otherwise change it back to relative
14			if (scroll_top > sticky_navigation_offset_top) { 
15				jQuery('#site-navigation').addClass('fixed').css("top", -nav.outerHeight()).animate({"top": "0"});
16			} else {
17				jQuery('#site-navigation').removeClass('fixed'); 
18			}   
19		};
20		 
21		// run our function on load
22		sticky_navigation();
23		 
24		// and run it again every time you scroll
25		jQuery(window).scroll(function() {
26			 sticky_navigation();
27		});
28	 
29	});