Bike fit is one of cycling's eternal rabbit holes. Every millimeter of saddle height, reach, and drop has been studied, argued over, and re-studied. Most formulas involve inseam measurements, flexibility assessments, and a fitting session that costs about as much as a decent wheelset.
This calculator takes a different approach: apply the golden ratio to the key proportions of the bike. Saddle height as a ratio of inseam. Reach as a ratio of torso length. Stack and reach in φ proportion to each other.
Does it produce a perfect fit? No. Does it produce a remarkably reasonable starting point, often better than the "multiply inseam by 0.883" rules you find in magazines? I think so.
Built with Next.js, TypeScript, and no external dependencies beyond the math.