A bow that's perfectly tuned today will not be perfectly tuned 2-3 months from now.It might shoot great with field points, but broadheads will greatly magnify any misadjustments that have worked into the system over the summer.

The arrows you shot all summer might well be worn out too. Even though they shoot fine with field points,broadheads will greatly magnify any spine or straightness issues they've developed. Contrary to popular belief, carbon arrows are not good forever. They don't bend but they do warp. And they are susceptable to spine degradation.

Buynew arrows and retune your bow when it's time to switch to broadheads.