The question should be "why do most cyclist have such large rings"
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I recently changed out my road triple for a mountain bike triple (not just for touring) because the 50 was way too much for me. I like to ride at 90-100rpm which means I won't need anything more than a 44/12 until I can ride >48kph/30mph on a regular basis. I also find the harder I'm working the higher my cadence, I often ride at >110 if I'm working really hard so I really don't think I'll ever need more than a 44.