Join Date: Sep 2008
Location: Loveland, CO
Bikes: Two LOOK 585s, one KG461
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Anyone who states that more than 7-8 cogs merely produces more duplicate gears is wrong. You can produce a cassette with the same range of 12-27 (for example) and have anywhere from 5 to 11 cogs. The difference would be the jumps between cogs. The latest 11 speed 12-27 cassette has the following cogs: 12-13-14-15-16-17-19-21-23-25-27. A Shimano 10 12-27 cassette is similar, but the after the 19, it goes 21-24-27. To get the same range, there are two 3-tooth jumps between the largest cogs. The same cassette in a 9 speed version loses the 16T cog.
As for cog life, Shimano reduced their cog thickness by 10% to 1.6mm when they produced their first 10 speed drivetrains (four years after Campy). Campy made almost no change to their cog thickness with 10 speed.
The new 11 speed cogs have the same 1.6mm thickness as Shimano 10. The width of the 11 speed chain roller was only reduced about 2%, so there shouldn't be a significant reduction in chan life. Most of the width reduction was accomplished by reducing the side plate thickness and using stronger material with no weight reducing holes punched into the outer plates.
Of course if the cog thickness is reduced by 10%, there will be a corresponding reduction in cog life. That makes it more important to learn how to manange chains and cassettes for optimum cog life. You'll get greater cog life by alternating the use of 2-3 chains rather than using only one until it's worn and then installing a new one. Chain skip if far more likely when a new chain is installed on worn cogs. If you alternate the use of several chains, you'll never install a new chain on overly worn cogs and you won't get chain skip from the new chain mismatch.
Another common mistake is relying on a Park chain checker or similar tool to measure wear, rather than acutally taking accurate measurements of elongation with a scale and roller wear with calipers. The Park tool always exaggerates it's wear measurements by combining elongation and roller wear into one meaningless reading.