I race a 08 YZ 250X in enduros in the "A" class. I bought the 21" NueTech Tubliss which was the only one available. I replaced a super heavy duty Michelin tube. Good things: 1. MUCH better front grip. The front end has always been loose in turns, but now the front stays put and the back wanders. 11lbs worked great. 2. Thanks to reduction in rotating mass the front brake has better stopping power. I was considering an over-size disc until I installed the Tubliss. 3. The front follows the ground better and almost seems softer in the first couple inches. 4.There seems to be less pounding passed through the bars to my arms. 5. No risk of pinching a perfectly good tube on installation. 6. Quicker tire changes. Less Good: 1. They suggest a new tire with an new Tubliss. I installed a "one race" Michelin and there was a slow leak. The indentations from the old rim lock creates a space for the air to leak out. I think that for racers that switch between practice and race tires, you may spend some extra time lining up the rimlock markings with the rimlocks. I will be the first in line to get a 19" for the rear.