OK, let me see if i can explain this right..
Rear Wheel
Cog1 14T
Cog2 18T
Chainring
Ring1 42T
Ring2 38T
Basically,they would all stay on at the same time, but only Cog1/Ring1 or Cog2/Ring2 combination would be used at one time. Is this possible?
I'm no expert, but probably possible if you get your spacers right on the rear hub
I take it that gear1 is road and gear2 is offroad?
Anyway it's all down to chain line and chain tension. If you've got the right spacers on the back wheel then chain line is no problem. Personally that's where my knowledge ends as I have a slidey dropout, so I don't need a tensioner and so I don't know how easy they are to get right.
Of course you'll be wanting 2 chains of differing lengths
Is that not referred to as a dinglespeed?
If you don't have a drop out that will take the slack in your chain you could use a phil wood philcentric BB to take up your chain tension, or a standard tensioner which isn't as practical, for offroad anyway.
Its called a geared bike 😆
have a search for 'dinglespeed'
/edit - beaten to it while I took a dump.
Ah, good stuff.
Trb - yes, correct. Gear1 will be for commuting, and gear2 for weekend singletrack bash.
I will be getting the new Salsa Ala Carte, which i think will be very good for this kind of set up. The new alternator drop outs, should make chain tension quite easy.
Any photos and set up descriptions?