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Do you really want that low an off road gear? A standard 2:1 ratio isn't that bad for spinning along to the trail, and would be less of a pain to deal with. On the other hand, if you're using a mech to tension and not trying to match the chain length between gears, you could use a 34:17-20 and 34:14 combo, not have to use two different front rings, and get a slightly higher road ratio to boot, or a 36 front for closer to 70gi on the road
I want to build my MTB up again dinglespeed. One gear for the relatively flat commute and getting to the trail-head, and another for pottering round trails. I'm thinking this combination (circled figures) could work well. I'll use a butchered road mech for a tensioner.
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