I,m shooting a 45/50 spine woodie with 135 gr.broadheads.Want to go to 165gr. broadheads.what spine shaft should I go with 50/55? Shooting them out of my HHbows.

Sounds ok, may have to go to 55-60

depending on the length of the shaft, 50-60 short shaft under 28" and 55-60 for 28" and above. That gives you play room for adjustment.

Assuming ALL other arrow specs are the SAME, a 30 Grain increase in point weight should require a 5# spine group increase.  I'd start with one of your current arrows, remove the 135 and put a 165 on and see how it goes.

Arne

I agree with Moebow.  Most bows will handle a range of spines quite nicely.