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Discussion Starter · #1 ·
I've been curious about this for a while. How much of a speed gain will typically be seen by going from an 80% let off module to a 65% let off module? If it's significant (say 10-12 FPS or more) then I might be interested in trying it out a little bit after hunting season ends.
 

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as previously mentioned, it depends on the design of the cam, with PSE's current hybrid and single cams the letoff is determined by an adjustable draw stop that limits or allows full rotation of the cam/cams. in this case there will be no difference in speed between 65 and 80% becuase the rotational differences are so minimal.

on a cam that has different modules for 65 and 80% letoff the 65% will generally be 3-5 fps higher due to an increase in energy storage (same rotation between the two but there is more stored energy)
 

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My Vectrix XL has a draw stop for 65% or 75% - you can also take out the stop and go with something in the 80% range with a slightly mushy back wall. I haven't noted any difference in speed among the three settings.
 

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Discussion Starter · #5 ·
My Vectrix XL has a draw stop for 65% or 75% - you can also take out the stop and go with something in the 80% range with a slightly mushy back wall. I haven't noted any difference in speed among the three settings.
thanks for the all the info guys.
 

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With to days bows and cams most are more effcent at 75 to 80% than at the lower ranges. 5 to 10 years ago it was a differ. story.
this is not the case, the market has driven the 80% market, on a lot of models the efficiency is the same no matter the letoff. yes most bows have the modules designed for 80% (its based on cam rotation and cable to string ratios) but cut manufacturing costs by short stoping the cams from going into full rotation for increased letoff and obtaining the lower letoffs like 65%. the bows are still just as efficient at this short stopped position, but are storing slightly less potential energy at full draw because of the decreas in cam rotation (a slight change in draw length)

some companies like BT in the past have made smooth and speed modules to give their customers the choice of letoff and draw force curve for speed or less aggressive. with their rotaing modules now they are doing the same thing as PSE, Hoyt, CSS/Horton and many other companies for customers that want decreased letoff. Mathews I belive has the same or virtually the same efficiency numbers for both their 65% and 80% letoff cams and the 65% letoff cams shoot a little faster because of more stored energy at full draw.

later
jkeiffer
 
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