Originally Posted by
pakossa
Main reason for measuring this in some fit formulas, is to compare it to the length of your inseam, to determine if your torso is shorter or longer than average. If that shows your torso is much shorter or longer than average, then it's likely your reach to the handlebars will likely need to be shorter or longer than average (though flexibility/core strength can also affect the ideal reach).
If your ape factor is greater than 1, your arms are long. Less than 1, they're short. If your legs are greater than 46 percent of your total height, they're long. Less than 45, they're short. Or something like that.