The stack-to-reach ratio compares how tall a frame is (stack) versus how far it stretches you forward (reach). It's the single best number for cutting through marketing claims and understanding a gravel bike's true character — more telling than either measurement alone.
A ratio below 1.45 gives you a low, aggressive, race-oriented position — fast but demanding. The 1.45–1.55 range is the versatile sweet spot most riders should target, balancing comfort and efficiency for mixed-terrain adventures. Above 1.55, you're in endurance and bikepacking territory, with an upright position built for long days in the saddle.
Choose based on your priorities: racing or going fast, lean lower; exploring and all-day comfort, go higher. Just don't assume more upright always means more comfortable — being too upright can actually cause hand numbness on longer rides since your weight shifts differently.