I've got a set of new limbs the same length as my current ones, but they're going to require a 1/2" shorter string to reach my brace height. I think that's too much to try to get from twisting the string, but is there a good "rule of thumb" of how much can be achieved safely and without affecting performance? I shoot ultra skinnies just for clarification. I would guess high strand count stings may tolerate more shortening by twist.
I've read where you shouldn't exceed a maximum of 1 to 2 twists per inch, but I see that I exceed that on some of my bows. The rule of thumb is that you shouldn't twist to the point that the string binds up. As a practical matter, if you're using an ultra skinny string to reduce weight and increase arrow speed, you're kind of defeating your purpose by twisting the string more than necessary, which has the effect of thickening the string.
For dacron strings, I've been told more than 20-30 twists for 60-62" bows will signficantly shorten string life. This is because the more twists the tighter the strands are held together making for more strand to strand abrasion as the string stretches during the shot. Newer string materials with smaller diameters are more abrasive than dacron. The potential saving grace is the newer materials don't stretch nearly as much as dacron, so there might be less strand to strand movement.
IMO, that's too much to try to twist up a skinny string. Would work OK with 12- to 16-strand string.
I agree with Orion. I put way excessive twists in a skinny string once that broke after a few shots.