The lowest gear ratio tells you how easy it'll be to pedal up steep climbs — it's calculated by dividing your front chainring teeth by the teeth on your largest rear cassette cog. A lower number means easier climbing. For example, a 38-tooth chainring paired with an 11-46 cassette gives you a ratio of about 0.83, which is quite friendly on hills.
If you're planning loaded bikepacking trips or tackling steep, loose gravel climbs, aim for a ratio below 0.80 — your legs will thank you on long days. For moderate terrain without a heavy load, 0.80 to 0.90 is a solid range. Ratios above 0.90 are really only suitable if you live somewhere flat or you're a naturally strong climber.
The biggest mistake riders make is not accounting for the weight of bikepacking gear. That extra 15–30 pounds transforms a climb that feels manageable on a test ride into a grueling grind. Always size your lowest gear for your heaviest scenario, not your lightest.