Getting close to my 24hr race, and the necessity of lighting is paramount. I installed the Trail Tech heavy flywheel for the 250/450/505 yesterday afternoon as TT claimed that it would provide enough extra power to assure that the battery would still charge at low rpm. The worry is of course that with an extended load on the electrical system that I would end up running out of battery somewhere to the left of nowhere with a dead bike and no kickstarter. With the HO stator still a little ways out yet (and I have learned the hard way that it is best to have a spare, so I did not want to have the stock one redone) I decided to go with the large flywheel. First things first. This thing is small. I am used to the parts inside my XR650R, so the fact that there is even enough capability with a stator and flywheel so small is quite amazing in my eyes. Install was straight forward. Just remember that for those of us with 450/505s that the instructions were first laid out for the 250 motor, so the descriptions of removing some of the parts don't quite jive as the 250 is a no e-start situation. Important point number two. Don't forget to put in the spacers for the trigger. If you do forget, no matter how much you push the button it won't fire. So if you hurry like I did, you will have a bike with a near dead battery. When finally fired up, the change is immediately noticeable. The bike does rev slower (duh), but it is in no way a slower bike. The sheer rush of power that we are all addicted to with the 505 is still there, just now it is much easier to dial a wheelie. Throttle control was much improved. As a side benefit, my 505 starts much easier. I am sure the extra mass has a lot to do with it. It will now happily start in gear without any reservations and the clutch drag that seemed to be there is now gone. On the charging front, remember that I had an issue with the battery almost dying down due to my utter stupidity. At idle the battery is currently showing a volatge across the poles of 14.7 as it charges. Still at idle, when turning on the HID race light, the voltage across the battery dips to 11.5 on initial ignition of the HID, and as it warms up the voltage across the battery increased to 13.4 at idle. So the electrical system now has some definite power behind it. The large flywheel may not be for everyone, but if you are looking to make sure that you aren't going to puke out your battery in the middle of nowhere with lights or a fan, this may be the way that you want to go. I have had two others ride it in the last 24hrs and both of them are ordering the flywheel for their 505s this week. I have so far only ridden it off road and it is a great bonus there. I will report again after I have spent some time on the MX track to see if it is an improvement, hinderance, or neutral there compared to the stock flywheel. I have a puller in my toolbox so I can switch them out at the track for a direct comparison.