Not so - I decide to forgo my rarely used third ring before I discovered that Sram road and MTB components are compatible.
I'm using a 36/22 x 11-36 combination.
36 x 11 gives me a 25mph top gear at 90rpm. I'll have to be going down a mineshaft to need higher.
22 x 36 gives a 17.4 gear inch low gear - plenty low.
I find the gear progression quite natural and comfortable.
36x11 equals 23.6 mph at 90 rpm. 88.4 gear inches. Sort of quick. But with a tailwind and level ground, you can easily go faster. Almost all down hills will get you much faster than 23.6 mph. I coast down all hills without pedaling faster than 23.6 mph. Vast majority of people would be unhappy without a higher gear.
22x36 low gear equals 16.5 gear inches.
Personally, I'd opt for a 40-22 crankset over your 36-22 rings. Combined with a ten speed SRAM 11-36 cassette of 11-13-15-17-19-22-25-28-32-36. You would have 15 usable gears on your 20 speed bike. Your 36-22 gearing results in 14 usable gears.
One of the problems with double mountain bike cranksets on touring bikes is they do not come from the factory setup like this. Every touring bike comes with a triple crankset and shifters/derailleurs for a triple crank. If a person wants to use a double crankset on a touring bike, they MUST build it themselves. Either buy all the parts and frame and build the complete touring bike themselves. My choice. Or buy a stock bike with a triple and replace shifters, crankset, derailleur. Costly and wasteful.
Not quite.
36 x 11 using 29" x 2.3" tires = 94.7 gear inches and gives just over 25mph @ 90rpm.
And 22 x 11 gives 17.7 (my typo previously).
Personally I don't care how fast a bike goes downhill - and I don't know why any other cycle tourist would either. The subject is touring, not racing. Once you have reached to the top of a climb you have earned a breather on the descent. If you spin out, you spin out - so be it (for me that would at > 130 rpm - around 35mph).
So odds are I will be coasting downhill, and on the flat I definitely will not be pedaling a loaded bike at anything like 25mph unless there is a
very strong wind behind me.
However, this bike is set up bikepacking. Sram have plenty of chainset options for higher overall gearing if you want to build a road tourer.
As I have posted, the gear progression is natural and comfortable. The amount of overlap between the rings is quite convenient and reduces the number of chainring shifts.
On the road it works extremely well. This not mere opinion, this is actual experience riding the bike. It is so nice to ride that I'm considering upgrading the Shimano 44/32/22 x 11-34 triple arrangement on my road tourer to the same, or more likely a 2 x 11 arrangement.
A 38/22 chainset will give the same high gear with 700 x 35 tires which will suit me just fine.
In fact there are quite a few factory offerings now with 2x MTB drivelines. They are marketed as adventure bikes and are redefining touring bikes. They are equipped for touring nonetheless, with alternative driveline arrangements, fender and rack mounts and multiple bidon mounts, with frame clearance for decent sized tires too. There are a just few examples listed here.
2016 Buyer's Guide: Best Adventure Bikes
