I have a 12oz. weight on my 99 and I think it works very well. It helps with traction on trails and lessens the hit a bit. Where I notice the biggest improvement is on hills. Since there is more reciprocating mass, the bike is almost stall-proof. My bike has strong low end to begin with, so the weight really helps when I'm on tight single track. The bolt on weights are easy to install. And they are easily removed when it's not wanted or needed. Personally, I think it helps me on the track, also. Since installed, mine has never been off.