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Importance of Correct ATA Length
Yesterday, I started to set up my old Hoyt Trykon for the upcoming 3D season. I installed a new set of cables and used the old string as there was nothing wrong with it and I didn't have a new one anyway. After installation, the ATA was 1/4" longer than the tune specs. I have not corrected it yet. I adjusted for cam timing, but have not otherwise tuned the bow. The draw length feels good. I have not measured brace height, actual draw length, or draw weight. I have not been able to find information on the effect of leaving the ATA a little long on overall tuning. Does anybody have any information on this? Without trying to over think it, I would think that it may shorten the draw length and decrease speed.
I wouldn’t worry about it. Timing is more important. Have you shot it? If it’s shooting bullet holes through paper and Broadhead tunes then you’re in better shape than 75% of hunters.
I have not shot it yet. This is set up for 3D only and not BHs. Typically, I'll paper tune, then walk back tune, then group tune. I'm usually pretty anal about my tuning. I've always been within 1/8" of the factory ATA spec without much ado-probably just by coincidence. But, is adjusting to the factory specified ATA that important or just a waste of time.
What was it before you took the old cables off. I am sure that your string is longer than factory so that will affect your set up too.
I didn't think to measure it beforehand. I use Winner's Choice strings and cables. But those had been on awhile. So, I will assume that they stretched some including the string. I usually add or subtract twists to the string to adjust brace height and not adjust the overall ATA. To adjust the overall ATA to shorten it I would add equal twists to the buss and control cables as well as the string. Once done with that I would adjust the timing, brace height and draw length. I've just never had to do that before. Assuming that the buss and control cable were of correct length and the string stretched, I could just add a few twists in the string and see how that affects the ATA.
I think that you should always start by getting the ATA correct. This will get the limbs properly loaded. Then adjust the DL and timing. With a long ATA you may have reduced your draw weight with your limb all of the way in. If you are happy with what you got I would leave it seeing that you are already done. If you find that you are having problems with pondage or DL you can adjust your ATA. If the timing is right it should shoot well.
It has always been my understanding that Hoyt's use the buss and control cable to set the brace and AtA length. In theory, you should be able to take twists out of the string to ensure the load is on the cable system, re-twisting the string once things are in spec setting your peep rotation. In saying that, your optimum performance is going to come from having everything as close as possible to factory specs. As you alluded to, leaving the AtA long will reduce the overall poundage achievable because you are taking out some of the limb preload. If you time and sync your cams, even with the longer AtA, you should still get good shot quality and grouping, just not optimal in all areas of performance.
As with most tuning threads, you will likely get 2 different responses. The "close enough" crowd will tell you that you're worrying about minutia, and to just shoot it. The "OCD" crowd will tell you to start out tuning by getting the bow as close to factory ATA and brace height as you can, then fine tune from there.
I happen to fall in the latter crowd. I always start with factory ATA and brace, then go from there. Once I get the perfect tune, I put reference marks on everything. That way, if anything changes, I can quickly make the necessary adjustments to get back to tune without starting from square one.
A friend who ran a bow shop for 20 years has told me to never take out twists, but rather to add to the opposing cabling.
ATA is nothing more than a measurement that indicates the complete harness assy is to the same spec as the bow that was built when the engineer set it up. If you twist cables or string to get your draw length and/or holding weight where you want it, which is what you should be doing, the ATA and Brace will both be off from the initial measurement.
Matt, I'm right there with you. I've never been in the close enough group. I also now remember a thread in Archery Talk by some Hoyt guru. I think I remember that he untwisted the string and used the cables to set the ATA and then added the twists back into the string and went from there to adjust brace height and draw length. I know I printed the thread. Now, if I could only remember where I put it.
Twisting the string won't affect ATA. I think it's always best to start where the bow was designed and make any changes you want from there. As mentioned, that's where the limbs were designed to be loaded, etc. If you know what you are doing and understand the implications of any deviations, that's fine but start off at correct specs.
Factory ATA is an "average". I would never use it as a be-all, end-all. ATA changes with draw weight adjustments and string length adjustments.
If you have a press, remove and measure each string and cable, then twist them to as close as you can to what they are supposed to be. Once you get the cam timing correct after that, you can fine-tune draw length with just the string (never mess with the cables once they are the proper length). The string itself can be shortened or lengthened without disrupting the cam timing to adjust DL to that sweet-spot.
Once you have everything where it shoots well and feels well. Then go ahead and measure brace & ATA and write it down for future reference the next time you change strings & cables.
Thanks guys. I just went ahead and did the adjustments to correct the ATA, removed the cam lean (I got frustrated and forgot to check it before), and re-timed the cams. Brace height and draw weight are right where they are supposed to be. I figured I'd wait to get to the range before fine tuning the draw length. I don't really measure it anyway. I just adjust until it "feels" right for me. I'll then tune the rest. BTW I did find the Archery Talk article. It was written by Mike "Javi" Cooper. He takes about 10 twists out of the string to be sure it is not affecting the ATA, adjusts the cables to the correct ATA, times and syncs the cams, adds the 10 twists back into the string, and goes from there. Makes sense to me. Thanks again for your help.