Originally Posted by
Gonzo Bob
The two big rings with a small third ring is called half-step plus granny. ... This type of gearing makes sense when your freewheel cogs jumps are large, typically in the 20+% range, so that the big/middle jump of ~10% "half-steps" the freewheel. A typical freewheel used with half-step granny might be a 13-32 or 14-34 6-speed.
When your freewheel cog jumps are smaller than 20%, it gets harder to half-step and it makes more sense to use a crossover such as 52x42x30. That's why you don't see half-step+granny on today's new bikes. ...
Actually, I use a 49-46 or a 45-42 half-step with about a 13% progression in back, for my favored 6-7% ratiometric progression. There are few combinations better than 49-46/14-16-18-20-23-26. Unfortunately, some of the newer spiders won't accommodate half-step gearing without the chain falling between the rings -- this is where I really like 1.5-step, rather than crossover.
In the mid 1970s I set up my Nishiki to run with either 50-47/14-16-18-20-23 half-step or 50-42/14-16-18-20-23 1.5-step. To adapt for a hilly course, I simply swapped the inner chainring, a 5-minute operation.
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Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069