A side note - as I read this discussion and others like it in the past, it occurs to me there seem to be representatively few SRAM users in our discussions. It’s like everyone’s assuming Shimano all the time. Maybe a drivetrain poll is in order?
Done. Go vote! What’s your drivetrain brand poll? NOT argument!
Sram has all but skipped 2x for all-road bikes. Their push to 1x, especially driven rightly by CX is not the perfect solution for all gravel riders.
I think a 12s variant with something between 10-50 Eagle and 10-42 11s may give appropriate range and improved hear steps.
Shimano Ultegra RX gives a direct 2x11 option with clutched performance. It’s an important development because we need solid clutched derailleurs, IMHO.
True @mcneese.chad that Shimano RX clutched derailleur is a big step. That said, even with the Ultegra RX RD in a pure Shimano drivetrain, you’re somewhat limited on gear range. It only supports up to a 34t cassette and their smallest chainring is a 34 - so that’s just 1:1 gearing. For easier climbing gear than 1:1, you have to either go off-brand rear derailleur accessory (like the Wolf Tooth that’s been pointed out) or off-brand sub-compact chainrings.
I’m helping a buddy build up a new gravel bike right now with an Ultegra RX rear derailleur on an Ultegra group, except he’s going Easton crankset specifically to get the sub-compact, gravel-friendly 47-32 chainrings. Then, at 32x34 he gets slightly easier than 1:1 climbing gear.
Plus, for the high end don’t forget that tire circumference affects your gear ratio too - so while many roadies might shudder at anything smaller than a 50t big ring, if you calculate that on a 25mm tire vs. a 40mm tire you’ll see a big gear ratio change. So the 47 big ring there ends up being a better, more usable big gear. Plus add in increased rolling resistance from dirt and gravel too.
Seems like for areas with more moderate grades maybe gaps between gears are more important, but for steeper grades range becomes more important. (On gravel rides I never feel the gaps in my 1x setup - only when using it on a pure road ride with gentle grades do I notice them).
I run a SRAM 1x with 42 up front and 11-42 cassette. Works for me. I wanted 1:1 ratio and the 11 cog gives me all the speed I’ve ever needed even for paved sections. I think a sub-compact chainring might be the optimum but there were limited choices a couple of years ago when I bought my bike. Most then came with standard compact which I did not want.
Here is what I got from wahoo about the eagle on the KICKR, might solve your problem
Hello Mike,
Currently a 12 speed cassette will not work on the KICKR, But we have had success with using this Sunrace 12 speed cassette http://www.sunrace.com/en/products/detail/csmz90
It uses a 11 speed spline but 12 cogs so it will work on the KICKR and we have tested this on a Sram Eagle set up and it works perfectly.
Cheers,
Mike G
I mean, I specifically mentioned that gear ratio because it’s what he said he used. I realize that terrain varies greatly, but in my mind that’s where 1x is better than 2x. You can swap out your chanring for something smaller, cassette for something larger, or both.
I say this as someone who exclusively rides 1x. I change the cassette and/or chainring on my gravel bike depending on specific events, and stick with a 44x11-36 or 11-40 for all “generic” rides. My road bike is 50x11-32, which works find for where I live.
I’m similar @summerson, except all on one bike. Just swapping wheels, cassettes, chainrings and even chains (to account for extreme chain length differences from one combo to another). So my standard road setup is a 44 ring with an 11-36 cassette. For the most extreme gravel I’ll be on a 38 ring with a 10-42 cassette. And I’ve got all the ring sizes in between!
I would love to put a 1x with a 12 speed cassette on a gravel bike, but this option wouldn’t work nicely with the Wahoo KICKR trainer. Sure, you could go through the hassle of fiddling with the adjustments on the derailleur to get it to “sort of work” on the trainer, but that’s simply too much hassle. I’m leaning towards the 40T x 9-46 e*13 route, maybe Di2 … my workable cadence range is ~80 - 105, so I don’t imagine the larger steps of this combo are going to present too much of a challenge for me.
Next question is crank length—172.5mm vs 175mm. I’m 6’ with a 32" inseam, and I’m building up the Ibis Hakka MX with a 58" frame. Until this bike, I’ve been exclusively MTB oriented and all my bikes have 175mm cranks … why would I drop down to a 172.5?
One thing I would add re: 1x (con side): Even with a clutched rear derailleur if you are descending on a fast rear cog (smaller gear) and go through some rough stuff the chain can drop. Chain tension is at its lowest when the rear derailleur is in that pos’n.
I’m sure all gravel riders have experienced potholes or wash ruts at the bottom of a hill. In all my hundreds & hundreds of competitive gravel miles I’ve dropped a chain like that exactly once. Even with a narrow/wide chainring. On the other hand hit a manhole cover on flat pavement @ 25mph and the chain dropped! 
Never had that happen with a 2x setup.
Hold the press–this could be a winner! If I can run eagle off the trainer, and the sunrace CSMZ90 on the trainer, without having to fuss with fine-tuning adjustments to get the shifting, its new bike and new trainer time.
Was that a note from Wahoo?
I’m still confused how you plan on running Eagle—are you going with a flatbar? Because drop shifters for Eagle don’t exist.
Agreed. I have not seen an answer to my question yet. No cable options I know for drop bars.
The only thing I can think of are the pending electronic options from Sram and Shimano.
It is from wahoo but I’m not sure of a shifting solution yet…looks like the folks below caught that too, does a 11speed shifter really have “11 clicks” or is it just +1 -3 and could work? Or is the indexing off?
Wahoo needs to know about the 12s issue since people likely want to use their modern, Eagle-equipped mountain bikes on the trainer. So it is important from that perspective.
And eventually, there will be 12s on road/gravel setups.
Maybe the new Campy 12-speed road shifters hacked to handle the uber-wide cassette range? 
I’m MTB guy and assumed an eagle setup could work, or maybe a Di2 shifter could be reprogrammed to allow for a 12 speed shift…wishful thinking? I have Eagle on 3 of my MTBs; a hard tail Santa Cruz Highball, Ibis Mojo 3, and a Borealis Crestone rigid fatbike. I’m waiting for the 12 speed shimano group to be released, and may go that route on a Santa Cruz blur I will have built up this winter for Leadville in 2019. I’m building the gravel bike as potential tip toe into the road waters–riding with cars around scares the bejesus out of me–and to use for longer outdoor training rides this fall/spring. MTB trails in my neck of the woods are not conducive to LT100MTB training, so I really need a different bike to get to higher watts outdoors on grave/paved roads.
Yeah man, sounds like you’re a bit ahead of the curve here. There isn’t a solution for 12 speed road as far as I know—at least not right now. 1x11 is all you’re going to get with drop shifters, at least for the time being.
Terrain and distances are also a factor to consider. At the end of some of my longer training rides for DK, I was thankful for the 2x that allowed me to still spin up the hills and motor along on the few flat sections.
If distance and terrain aren’t extreme, I don’t imagine you could go wrong either way.
1x10 for mine and I ride some big climbs with it and most of my races are 10k’ climbing with some pretty steep and loose gravel or single track. I’ve never had an issue. I also never have any problem hitting those flatter rollers and drilling it.
44T Drop-stop wolftooth up front
11-36 SRAM cassette on the back
SRAM Force 1 Type 2.1 Rear Derailleur
Gutted left brifter so it’s just the brake.
I’m curious what is wrong with this approach
2x compact with a 10x34
53 - 10 = 5.3 ratio
39 - 34 = 1.14 ratio
1x with 10x34 and 53 chainring
53 - 10 = 5.3 ratio
53 - 46 = 0.86 ratio
I know the 2x would give closer shifts but ratio wise the 1x of this config beats a compact setup,