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Why not use a double crank with a 10-42 cassette?

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Why not use a double crank with a 10-42 cassette?

Old 05-12-20, 12:05 PM
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Chris_W
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Why not use a double crank with a 10-42 cassette?

In brief: I've never see anyone use a SRAM 10-42 11-speed cassette with a double crank, but the Shimano XT 11-speed rear derailleur I have seems to shift across the 10-42 range just fine with the chain on either of the 26 or 36 tooth chainrings (Shimano 11-speed crank). The cassette is only 1 tooth off of Shimano's normally quite conservative specs. The chain is a Shimano 11-speed. So is there any reason not to use this setup?

The full story: I'm getting my hardtail MTB ready to sell. I rode it with a Rohloff hub, but that's now going on my e-cargo bike, so I'm putting a mostly-new 2x11 transmission on the MTB to sell it. A friend has an ideal pair of wheels that come with an XD freehub body and a SRAM 10-42 11-speed cassette. The hub is unbranded and has no markings (OEM on a Boardman bike) and when I removed the freehub body it wasn't any brand that I recognize, so I'm giving up on the option of trying to source a Shimano freehub body. So, to use these wheels I need to use this cassette.

I thought about offering the buyer the option of having a single front chainring, 30 teeth instead of the 26-36 double, but then I thought why would anyone choose that given the option of having a double at the same price? Surely 2x11 is better than 1x11. More gears and wider range is better, right? I still don't get people's obsession with eliminating chainrings - front derailleurs are quite practical and generally work very well (as long as they're not labeled SRAM). Anyway, that's a bit off-topic.

As long as no-one points out something that I'm missing then this bike is being sold with 26-36 chainrings and a 10-42 cassette. Why not?

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Old 05-12-20, 12:14 PM
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The limit of the rear derailleur's ability to take up chain slack is why you usually see super wide range cassettes used in 1x setups but not 2x set-ups.

But your cassette is a 10-42, not a 10-50, and your chain rings are 10 teeth apart, not 14 or whatever. Your max tooth differential (the amount of slack the derailleur has to handle) is 42, which is pretty close to slack a derailleur handles on a 10-50. It helps, too, that it's on a hardtail, and you don't have to worry about rear suspension travel.
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Old 05-12-20, 12:16 PM
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Originally Posted by ljsense View Post
The limit of the rear derailleur's ability to take up chain slack is why you usually see super wide range cassettes used in 1x setups but not 2x set-ups.

But your cassette is a 10-42, not a 10-50, and your chain rings are 10 teeth apart, not 14 or whatever. Your max tooth differential (the amount of slack the derailleur has to handle) is 42, which is pretty close to slack a derailleur handles on a 10-50. It helps, too, that it's on a hardtail, and you don't have to worry about rear suspension travel.
Yep, absolutely no problem with having a slack chain in the small-small and there's still a reasonable cage articulation in big-big, so I'm not worried about chain wrap capacity.
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Old 05-12-20, 03:28 PM
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Shimano made a mtn bike 2x11 setup using a 11-40 cassette option for XC racers so you aren't really pushing it much over the recommended going 10-42. As for why not use it? Because when mtn biking I don't need to be able to pedal at 35mph, it adds weigh and complexity. I don't need that gear range to make it simple. For a mixed use bike it can make more sense.
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Old 05-12-20, 03:59 PM
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Have you plugged your gears into a gear calculator to see what kind of overlap etc. you have?
How about after eliminating a gear on each end to allow for cross chaining?
I would imagine with some combinations that there is little gain. Especially compared to a "primitive" 3X9, which apparently has become overly complicated up front over the last few years with that FDER thingy.
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Old 05-13-20, 04:56 AM
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Originally Posted by Bill Kapaun View Post
Have you plugged your gears into a gear calculator to see what kind of overlap etc. you have?
How about after eliminating a gear on each end to allow for cross chaining?
I would imagine with some combinations that there is little gain. Especially compared to a "primitive" 3X9, which apparently has become overly complicated up front over the last few years with that FDER thingy.
I am quite happy with my even more primitive 3X7 setups....
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Old 05-13-20, 11:44 AM
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Originally Posted by Bill Kapaun View Post
Have you plugged your gears into a gear calculator to see what kind of overlap etc. you have?
How about after eliminating a gear on each end to allow for cross chaining?
I would imagine with some combinations that there is little gain. Especially compared to a "primitive" 3X9, which apparently has become overly complicated up front over the last few years with that FDER thingy.
It was a brilliant idea to put the chainrings on the rear and a cog from a cassette on the front and charge 5 times the cost of a normal cassette. Tell everyone it is simpler and lighter and amazingly better.
Cos no one could make a FD that shifted nice. It just couldn't be done.
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