I bought a new 2005 kx100 for my nephew. The power band hit was so bad that, when in wet and slippery soil, the rear wheel would slip so bad you couldn't control the bike. I put a 10 ounce weight on and love it. IMO, they ought to come with one on from the factory! You can still feel the hit but it comes on much smoother. Don't worry, it will still pick the front wheel of the ground when shifting into 3rd with no trouble and I weigh 165! They are quite easy to put on but I see no need to take it off. The kx100 is so light to begin with, it has trouble keeping good traction in the first place. I also put a 53 tooth on the rear to gear it down to keep it on the pipe more and seems to work nice also.