Hoyt ATA and BH question

[rhendrix]

Ok, so I've been shooting and tuning my CST and crunching numbers. Just wanted to verify some things real quick, Hoyt measures brace height from the deepest part of the grip, correct? And ATA should be measured from center of the top cam to the center of bottom cam, correct. I'm only asking because I'm not meeting the advertised speed according to several calculators and I think I need to add some twists to my cables since my ATA looks to be a half inch long, and my brace height is about 3/8 inch long. Not sure if that would account for 10 fps though.

Thanks for the feedback,
Ron

 

[OR Archer]

A2A is measured from the center of the axles not the cams. Brace is measured from the grip throat.

What cam size is this bow? Each size cam will have a different A2A and brace height measurement.

All specs for the 2014 CS Turbo can be seen here http://www.hoyt.com/uploads/tune-charts/e040ba48e9e3b1deddf4b927345e8e7dc4f40064.pdf

 

[RosinBag]

When you say calculators, do you mean chronograph? If you are referring to on line calculators based on inputting data, they are only going to be close at best. You need to shoot it through a chronograph to know what your bow is doing.

Also those specs are only exact in with one of the modules per cam size. I wouldn't get to caught up in exact measurements. ATA within a ¼" and BH within an ⅛" and you are fine.

 

[OR Archer]

Also those specs are only exact in with one of the modules per cam size. I wouldn't get to caught up in exact measurements. ATA within a ¼" and BH within an ⅛" and you are fine.

The modules will not change the those measurements at all.

 

[RosinBag]

My experience is if nothing changes other than modules, measurements will change slightly. I have always had to manipulate string and cable length slightly if I want everything back to spec or close to it.

But I certainly don't work on bows like OR does.

 

[OR Archer]

The modules don't actually contact the cables until the bow is drawn that is why they do not affect those measurements at brace.

 

[rhendrix]

OR, I don't know why I said center of the cam since the axle is the pivot point and therefore the center. To verify it's a #3 cam. I checked the tune chart prior to posting, so the ATA is off by about a half inch. Is that half an inch going to account for a 8-10 fps loss of a chronographed speed vs a calculated speed based on ATA, DL, arrow weight, et al.? I only ask because I wanna squeeze everything I can outta this bow.

 

[OR Archer]

Yes it'll effect the bows performance. I'd suspect you have quite a bit of stretch in all three strings. I'd take them off and measure them. I will venture a guess that with that much stretch your bow isn't making poundage which would attribute to your speed loss.

 

[rhendrix]

That's what's strange though, it's set at 72# and peaks at 74#

 

[velvetfvr]

I have to guess stretch in the string and cables but that is odd. Maybe just get a high quality set or custom strings now and start all over?

 

[rhendrix]

I have to guess stretch in the string and cables but that is odd. Maybe just get a high quality set or custom strings now and start all over?

This is probably what I'll be doing after Christmas, although I've been told that the Hoyt strings on it are pretty darn good already, and I haven't shot it all that much, so I can't imagine that the strings and cables have stretched.

 

[Ozz08]

I had kind of the same problem with my CST. I twisted my strings and cables to match the lengths on my limb sticker and was still off 1/4"-3/8" on BH, ATA, and draw length. Ph rage was maxing at 74.5 lbs. Then I checked the string and cable specs on the tune chart and it lists lengths that are about 5/16" shorter than what was actually on my bow. I looked into it further and found that some of the CST's came with harnesses that were a hair long. I got a custom set made to match the lengths on the tune chart for my cam and everything is dead nuts now. Pundage maxes a hair over 72lbs.

 

[rhendrix]

Oz, I might try that until I can get the funds together for new strings and cables.

What order did you start measuring and twisting your cables and string in? Figured I'd start with the bus cable, then control, then string. Then retime the cams again.

 

[charvey9]

I believe BH also needs to be measured with the stock grip on. If you running side plates, or have the grips off, and measure to the deepest part of the riser it would be off by about 3/8".

 

[MattB]

It sounds like your strings/cables have crept and need to be twisted back to spec.

I see a few folks refer to stretch above, and not to go all internet vocabulary Nazi, but stretch and creep are actually different concepts with creep being the relevant one here. Creep refers to permanent elongation of the string material, whereas stretch is temporary/recoverable elongation that happens during the shot. Creep can cause ATA and BH to change, whereas stretch does not. In the old days, most recurve/longbow strings were made of Dacron which had a fair bit of stretch that added a shock absorbing quality at the end of the shot. Most recurve/longbows made during that era could not be used safely with low/no stretch fastflight strings because it would damage the limb tips over time due to the lack of this shock absorbing stretch.

 

[Ozz08]

I originally pulled my strings/cables off the bow and put them under 100 lbs of tension and measured them. I twisted them up until they measured what was listed on my limb sticker and put them back on. Then added/ removed twists to get the cam timing right. I wasn't all that concerned with ata and BH off a little but in order to get the draw length where it should be I had things so twisted up it just didn't seem right. That's when I started looking into the string and cable lengths and found my bow came with different lengths than what was on the tune charts. When it comes down to it as long as the bow tunes up how you want it I wouldn't worry too much about ata and BH being off a little.

 

[rhendrix]

How'd you put pressure on the strings?

 

[Ozz08]

How'd you put pressure on the strings?

I added a small book to my draw board just for that purpose. Hook the loop on the j hook then attach the other end to the winch and bow scale. Just crank them tight with the winch until the scale reads 100lbs.

 

[rhendrix]

Guess I'll be building a draw board now!

 

[OR Archer]

You really don't need to measure the strings under tension. Just put a loop end on a peg and pull them tight and measure.