For MX racing, is it better to have taller front and shorter rear tires, or shorter front and taller rear, or even? From what I gather, the taller front and shorter rear is the hot setup (i.e 18" turf-tamers and riken fronts). Why is this so, and will it hurt to have 20" turf-tamers instead?

 

20" tammers are not bad but most people use the 18" tires to get out of the hole quicker and the smaller tire will not flex as much as the 20" tire just make sure you have you countershaft sprocket set up right for the type of ridin you do.