Quote:
Originally Posted by Gummee
The old math still applies: 1 tooth in the back is 3 teeth in the front.
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That math only applies for cruising gears. Since this thread is about very low climbing gears with roughly a 1:1 ratio of chainring size to rear sprocket size, 1 tooth in the back is worth pretty close 1 tooth in the front.
A bigger cassette in the back works only up to a point, because most road derailleurs will have a maximum sprocket size (and Campagnolo road derailleurs typically have a more limited maximum size than the S groups). Another disadvantage of larger cassettes is that they require a derailleur with a larger capacity (i.e. longer cage), whereas reducing chainring size generally doesn't require the derailleur capacity to increase. It should also be noted that larger cassette also usually means bigger jumps between gear sizes.