Looking at the tire options for our motorcycles, I see a lot of tires I would like to try that are 19 inch only models. Are the 18 inch versions primarily there to cut the tire and wheel weight over a 19 inch equivalent? Even the KTM's seem to come in 18 inch rears on most of their models.

Is the 19 inch rear only practical on higher horsepower motorcycles? A larger rear tire seems like it would roll easier over obstacles but, I also realize the difference between the two sizes is pretty small.

 

I belive that offroad cycles(vs. mx bikes) use the 18 inch rear because the tire has more sidewall heigth to it. It lets you hook up over trail hack better. KTM mx bikes will have the 19 inch rear.