Smaller dual chain ring setup on gravel bike

[Natepul]

Hello everyone, first post here! I am in the process of gathering parts to upgrade the drivetrain on my 2020 gt grade elite from 2x8 Claris to 2x11 sram. I want to get as much range as I can while keeping the 2x setup, and it looks like I would be able to use an e13 xcx cassette with a 9-34 or 9-39 range (I've already sourced a derailleur that will work with this). Given my top end range I've had on previous bikes, I would be able to go down to a 42 tooth chainring up front and still have more top end.

On the low end, I see that road chainrings tend to have a range of 16 teeth. That would bring my small ring down to 26 teeth (which would fit on my spider that has 110 bcd and 80 bcd) However sram mountain chainrings that go down to that size recommend that I pair a small 26 tooth chainring with a large 38 tooth chainring(12 tooth range), and that I pair a large 42 tooth chainring with a 28 tooth small one (14 tooth range).

Here is my question: does going down that far in size in chainrings limit the potential range down from 16 teeth, or is that just sram putting forth compatability numbers for mountain bike front derailleurs, meaning I should be fine using a sram road front derailleur?

I will be using a clamp on road front derailleur to be able to reach that far down

My guess is that it would work since I believe the relationship between radius and circumference is linear (2*pi*radius=circumference). I would appreciate corrections if I am incorrect

Whew, that was a bunch of words, I hope they make sense!

[Marin]

I ride the 9-39 XCX casstte in a 1x setup. With a 32t chainring.

I can pedal up to 60kph on descents. I actually did just an hour ago. Do you want to go supersonic?

I also have a 9-32 for road only riding - with a 38t front ring.

To answer your question: Front derailleur range is independent of ring size.

[Natepul]

Thanks!

On the top end, it appears that I would be getting a ratio similar to having a 51-11, so for the road side of my riding, it would be a touch faster than the 50-11 on my old bike. I will probably err on the 9-34 side for the cassette, as the ratio of 26-39 would rival many full on mountain bikes

[jemima]

10sp Sram notes, but I found the bottom end of the cage on a Red front derailleur hit the chainstay on a 2x with 40t large ring, when dropping down to small ring. Shorter cage length on the Sram front mtb derailleur, so that was fine.

With a 42t and Sram road 11sp front der., you may also strike the chainstay.

Bike currently setup with 40/22, using an XX front derailleur.