Originally Posted by
burnthesheep
And since two in the front is worth one in the back, going from 50t/11 to a 13 for efficiency would mean needing a 54t in front.
That's not the way ratios work. The difference between 11 and 13 is roughly 18%. The difference between 50 and 4 is roughly 8%. You'd need a 59t paired with a 13t for the gear ratio to be the same as the 50/11