Thanks, that helps…but leads to a follow up question: a 34/40 combo gives a 0.85 ratio whilst a traditional drivetrain with a sub compact 28/44 crank and the largest standard campa cassette 13-29 gives a ratio of 28/29=0.97. So even with a sub compact crank I would need at least a 36 large sprocket in order to get to a lower ratio: 28/36=0.78. on the other hand I read that the ratios do not give the full picture…a large crank with very large cassette is allegedly not the same as smaller crank with not quite as big cassette even so the gear ratios might be close…any experience with that?
For mere mortals like us, ratios are ratios, regardless of the chainring/sprocket combination that achieves them. That being said, a given gear using a large/large combination (eg, 50/25) will technically be more efficient than a small/small combination (eg, 34/17) because the milder chain wrap around the larger gears induces less frictional power loss. However, a straighter chain line (eg, 50/13) will be more efficient than a crossed chain (eg, 50/25) - all this to say, differences in power transmission efficiency as a result of what the chain is doing are the most marginal of marginal gains compared to available gears, and of academic importance to anyone but high-level competitors.
When you’re grinding up a hill, you’ll be praying for another, lower, gear - not a slightly more efficient drivetrain. Available (low) gears are king.