How do I figure out what length string I need for a bow that has no markings? I don't know who made it and it doesn't have an existing string. Is there a formula that can be used by measuring tip-to-tip or something?

Also, how is the AMO length calculated?
My buddy has two AMO 60" recurves (a Bear and a Shakespeare) that are about 4" different in length when they are unstrung. Would the same string work on both bows?

AMO length is three inches longer the actual string length to bring a bow to proper brace. So bows can have much different actual lengths but the same AMO because they need the same string lengths to make their recommended brace. A bow that has 6" brace and one that needs 8" brace both using a 60" actual length string would be of much different length when unstrung. There is no formula for it depends on the bowyer's recommended brace height.

To get the bow length, use a flexible take (like a steamstress' tape--a cloth or plastic tape) and start at the "top" of one of the string grooves.  Measure along the side of the limb, following the contours of the limb, through the center of the riser, down the other limb to the "top" of the other limb tip.  

Most bows will get a string 3" to 4" shorter than this, but it will depend on the bow, if the bowyer followed AMO specs, etc.  I've seen string lengths run from 1.5" shorter to 6" shorter.

The same string will probably work on the Bear and the Shakespeare--most of those get a string about 4" shorter.  

Like Vermonster said, according to AMO specs the AMO bow length is 3" longer than the string that puts it at the proper brace height.  The "catch" is a lot of bows don't follow AMO specs.

Chad

are you by chance referring to the unmarked bow your friend found in an attic you suspect may be a clif coe bow?

because if so there may be an amo spec somewhere.

If not disregard

Yep, that's the one. There isn't any writing on the bow and I'm still not positive it's a Cliff Coe bow or not. Let me know if you know where I might find some specs on Cliff Coe bows. I didn't find much doing a web search.

What's up Troy, I just noticed the Portland location. You find a left handed bow yet? The thread that I started about the bow with the stress cracks in the limbs is the bow Andy ended up buying.

Vermonster nailed it for you.  An AMO 60 bow string is 57" loop-to-loop. The length of the bow itself is irrelevant.  As for the unmarked bow, I'd start with a string 3" shorter than the bow and try shooting it.  Keep twisting the string till you get a brace ht that works or until you need a shorter string.  When you get a brace ht that works, measure the string loop-to-loop and add 3" and you'll have the proper AMO length for that bow.  Then mark the bow!

All I got on Cliff Coes is this site
http://www.archeryarchives.com/coe.html

It has some specs.

If you can visually find the bow then you might be able to get the AMO length.  Otherwise use the seamstresses tape or a string to run along the bow they way that was said earlier.