The inseam method is almost as old as the days when the salesman would simply pull down the largest frame that didn't crush your nuts when you straddled it. These days, manufacturer recommendation is the best place to start if you're starting with an experienced, reputable brand. But it pays to understand your individual morphology. Are your proportions average or do they have eccentricities? They might limit your choices or indicate adjustments in size, stem, handlebars, and cranks.