For whatever reason, you want to pull the trigger on your 1x commuter/road bike. I just finished the final piece in my somewhat haphazardly approached, yet successful conversion. Some things I did right and lucked through others. For those interested, I suggest the following approach:
What are YOUR acceptable limitations?
If it ain't no fun, you won't want to ride it. Whether you use a gear inch calculator, or just the way you feel while pedaling, determine what range you want. I started with a 3x9 mtb, ~99-17 gear inches. I almost never used the upper most and lowest most ends. Smartly, I fixed the front derailleur into the middle, and rode for a month. Got a great appreciation for what that range (in my case, 32x 11-34) could do for my body and terrain dynamic.
What are your priorities/what are you willing to give up?
Likely, you will compromise around prioritizing downhill speed and climbing ability. I naively went for biggest back dish and the largest chain ring that could match my climbing requirements and maximize my downhill speed. I expected there would be an easy engineering solution, and almost "screwed the pooch".... More on that in a moment.
Can I do this cheaply?
Mostly, no.... You
can set the front derailleur screws, ditch the left shifter/cable and be done with it. No cost but time. Other than that, if you are going to change range, parts and labor are going to cost you.
What I want vs the drive train!
Go into this understanding that cranks, chain ring, chain ring bolts, bottom bracket, chain, rear derailleur and sprockets may all have to be replaced with associated labor/tool costs. I almost messed up by choosing 40x 11-50 without considering chain stay length and the necessary link count. Got insanely lucky to have the combination come out to 116 links. Used a standard 9 speed chain. 10+ sprockets require thinner chains. Yes, you can fit as many sprockets as your drop out will accept (common mtb = 135 mm). If you go outside your derailleur's capacity, a goat/road link will be required ($5-$35+). The basic Shimano Altus rear derailleur + $6 generic aluminum alloy "goat link" has worked flawlessly for me. Narrow Wide chain rings will prevent chain drops from foreseeable road use. Avoid a riveted crank so you can customize as needed. Chain line is very important and an appropriate bottom bracket will be required.
Sounds like not so much to consider, but doing the above homework will save you pain. And you just might decide it's not worth it.
As a counter-intuitive footnote: I actually placed a 28 tooth, 64bcd chain ring inside my 40 tooth, 104bcd. It is a manual "bail out", and certainly not unique. I call it the "Boy Scout" ring. Just in case I meet steeper hills, load my CamelTrek heavily, or get a bent outer chain ring, I have an emergency solution. Tested it today, and I get excellent operation from sprockets 1-7. Top speed is garbage, as I'm only achieving 45.5 gear inches. For hills, loads, and emergencies, acceptable.
Hope this helped amateurs, like me
Constructive questions welcome!