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
It's a good point, if I'm using a mech to tension anyway, there's no need to totally match the tooth difference. That said, I think I might go 34/18 and 38/14 to start, see how that works out.
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