Article by Marvin Long – Sep 20, 2006
Measuring Traditional Bows and Bowstrings
There is a lot of misconception about measuring bowstrings for traditional (conventional) bows and I would like to help alleviate some of the questions about these bows and bowstrings.
I have sat on the AMO (Archery Manufacturers Organization) & ATA (Archery Trade Association) Specifications committee for some 20 years and have been involved in many discussions about archery equipment specifications. I have also been manufacturing bowstrings commercially for 28years. I made my first bowstring in Boy Scout Camp in 1954.
Recurve and Longbows are historic items that are now being used more and more, which I am glad to see. Archers using the old style equipment will help keep alive the history of our sport.
Ben Pearson, Earl Hoyt, Fred Bear and others that where involved in our sport in the middle of the last century and earlier, understood there needed to be standards set for the industry to make it easier for archers to enjoy the sport. Setting a standard for measuring the bow I am sure was one of many and since the compound has become much more dominate in the sport, many of the newer sport shop operators are not as familiar with the traditional bows.
The Archery Trade Association (ATA) specifies that a Traditional Bowstring should be labeled and sold by the length of the bow not the bowstring length itself. A 60″ Bowstring is for a 60″ bow, not the length of the bowstring. A Traditional bow is measured from string groove to string groove around the curve of the bows limbs, not directly from tip to tip. This measurement does not go into the curve of the handle but across theface of the bow limbs from string groove to string grove. This will give you the approximate length of the bow.
A Bowstring for bows over 40 lbs is measured by placing it over steel pegs and stretching it at 100 lbs of tension for 20 seconds. The measurement is taken from the outside of each peg. ATA Specs say that a bow should be properly braced with a string that measures 3″ shorter than the bow. So if a bow is 60″ is should be braced properly with a string measuring 57″ under 100 lbs of tension after 20 seconds. Bowstrings for bows of less than 40 lbs should be measured in the same manner, using 50 lbs of tension.
Bow Makers used a Bowstring Master Set of steel cables that would be designated as AMO (now ATA) Bow Lengths such as AMO 66″ (bowlength) but it would have an actual length of 63″ under 100 lbs of tension. If this cable should brace a bow correctly it would be classified a 66″bow. A Bowstring Master Set would range from 45″ to 69″ and would brace bows from 48″ to 72″.
A Dacron Bowstring, which will stretch almost an inch under100 lbs of tension, will look “out of the package” like it is 4 inches shorter than the bow. This is the reason you hear people speak about bowstrings being 4inches shorter than the bow length. This will only be for a Dacron bowstring and not under tension or actual length.
Because all materials stretch differently, measuring everything under pressure compensates for the differences between materials.The newer materials, like Fastflight do not stretch like Dacron, so they will look longer out of the package and more like the three inches according to ATA Standards. Strings are supposed to be measured with out any twist at that time.However strings are installed with some twists to give better performance and by twisting and archer can achieve better arrow flight. Some modern archers shoot with as many as 50 twists in a 70″ bowstrings. To get the proper length bowstring after twisting 50 twists you may have to start with a bowstring 1″ longer.
Strings that have been shot a long time and need to be changed will probably look longer than when they were new so going by the bow length is a more consistent starting reference.
Strings can be twisted to change their length and this can be done to change the bow set up so it performs better for each individual archer. This will help get better flight characteristics for the arrow; this is called tuning your setup or getting all parts working best together.
Marv Long measuring the Bear Grizzly AMO 58″, the ruler does not go into the handle but goes directly across the face of the limbs.
Shows the AMO 58″ bow measures 57″ from string groove to string grove.
Show 4 bows of different ages. The left bow is marked AMO 58″ the next bow is marked 60″ and the remaining two are not marked for length. They are all Bear Archery Bows The 3rd bow is a static recurve with the aluminum lamination and a running bear logo, The 4th bow is a laminated bow signed by Nel’s Grumley with no weight or length on it.
Shows the bow is marked as an AMO 58″ bow and this bow measures 57″ from string groove to strings groove but being an AMO St233andard it will brace properly with a 55″ AMO bowstring so it is a AMO 58″ bow.
All the non AMO marked bows do measure the length marked on the bow ie (60″ bow).
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