65 or 80 % let off?

[toddjler]

well I bought a bow, so I have a few questions on some of the things I forgot to ask about at the store. can someone tell me what the difference between 65 and 80 percent let off is, and what the +/- of either is? Thanks in advance

[CNP]

The +/- amounts to what feels better to you. Obviously you can hold 14 lbs longer than 24.5 lbs. Not many newer bows with 65% let-off? There is a reason why 50% let-off bows are largely extinct.

[KBF]

So what did you get?

[elkoholik]

Originally Posted by ehntr

The +/- amounts to what feels better to you. Obviously you can hold 14 lbs longer than 24.5 lbs. Not many newer bows with 65% let-off? There is a reason why 50% let-off bows are largely extinct.

Most target guys will use 65% to keep them honest and truer on their shot form/placement. Most hunters go for the 80% as it allows for the longer hold at draw without getting fatigued as quick which in turn gives them better shot opportunity in different scenarios.

[toddjler]

I bought a Mathews monster mr7 with 70 pound limbs

[Mike_W]

Originally Posted by elkoholik

Most target guys will use 65% to keep them honest and truer on their shot form/placement. Most hunters go for the 80% as it allows for the longer hold at draw without getting fatigued as quick which in turn gives them better shot opportunity in different scenarios.

X2 but most target guys wont be shooting 70 lbs either.

[SKSniper]

I don't think I would have gotten my moose in September if it were not for the 80% let off on my new bow, I was at full draw for well over a minute and I was barely able to pull it off, if I would have had my old bow (65%) I think it would be an all deer meat winter for me. Thank you technology

[toddjler]

so does let off make any difference in the speed of the arrow

[CNP]

65 is probably faster because you start off with holding more weight on full draw. I could be wrong. But even if I'm wrong.............it's like an insignificant difference anyway.

Bowtech RPM360 (360 FPS) has 80% let off

[elkoholik]

Originally Posted by ehntr

65 is probably faster because you start off with holding more weight on full draw. I could be wrong. But even if I'm wrong.............it's like an insignificant difference anyway.

Bowtech RPM360 (360 FPS) has 80% let off

There is a bit of change depending on bow for sure and as stated it is marginal. My target bow states 3-6 fps difference between 60 to 70% let off mods. Never seen a hunting bow nor other target state speed difference so it has to be close for them to not publicize it.

[SonofDixie]

I've heard that the round cams can tend to be more accurate than the oval..... Total myth?? I don't understand how it could....

I'd love to change my cam to the 80% .....

[LiveTarget]

The let-off does not affect the speed of the arrow as the overall draw weight remains the same, the let-off only makes holding the weight of the string less. The Potential Energy (PE) on a bow with a draw weight of 70lbs translates into the same Kinetic Energy (KE) value whether the let-off is 65% or 80%. Changing the arrow or it's charactistics such as head weight or fletchings will change the overall KE value however the PE remains unchanged.

[normanrd]

By changing the let-off you change where the cam rotation stops relative to each position. If you go less let off it typically stops the cam's rotation slightly sooner than in the higher let-off condition, talking strictly about cam rotation.

Because of this the area under the draw force curve for each let off condition is different. Since the area under the draw force curve is representative of the potential energy, theoretically the higher let-off condition should have a larger area under the curve, thus more potential energy, thus be able to shoot an arrow faster than the lower let-off condition.

In the real world, it usually doesn't amount to much, but it is highly dependent on what the shape of the curve looks like as you fall into the valley, since this is the only part of the curve that is different in the two draw cycle scenarios.

If you have ever had a bow that you were able to do this with, you likely would have noticed that the draw length felt slightly shorter in the lower let-off condition. On a draw board you would likely also see a slight reduction in draw length as well. This is in fact the difference in potential energy, caused by essentially shortening the power stroke (decreasing pe/area under the draw force curve).