Mine arrived on Friday. It weighs 8 oz more than stock . I love the feel of the engine with it on. It revs just as fast. It is far easier to ride slowly. For a rough track or trail it would be the hot set-up. For slick conditions it will be perfect. The cost was 99.95 from my local Yamaha dealer. I could have bought it for less here, but shipping would have to be figured in. http://www.parkeryamaha.com/browseproducts/Yamaha-03-05-YZ250-GYT-R-Off-Road-Flywheel.html It is an entire new flywheel with the weight welded on. It is the same cost, or less, than many of the add-on weights. Overall I am very pleased with the purchase. Besides, if I get sick of it, I can put the stock flywheel on in 5 minutes.