Adding teeth to the front drive sprocket is also an option, and the improvement in top speed for a given addition in teeth will be much more noticeable, but clearance in the drive housing may not be sufficient to allow for a bigger sprocket with more teeth. I also agree that the change from 41 to 39 is not big and should not make a huge difference in top end speed - an additional 7 kph sounds about right. I agree with you 100%, the problem is not cost, it is finding someone that has a rear sprocket that will fit a Phantom with fewer teeth (or, as noted a front sprocket with more teeth that will fit in the drive housing). Will a Phantom pull to redline in top-gear with a 41-tooth sprocket? If it won't (and it might not) it sure won't do it with a 39-tooth sprocket.Īlso, then idea of cutting and welding together a sprocket is nuts- they're way too cheap to consider doing something so fraught with potential problems.