I have a 2020 trek marlin. I'd like to change my rear cassette in the future but for now I'd like to know if I can change it to a 1x using only stock parts. Is this possible to do? Or would I have to buy a completely new crankset? Or just a chainring?
I've done this. A few considerations:
- To optimize your chainline, you want your remaining chainring to be the middle one. The chainring that's currently in the middle may be smaller than you want, but the big one may interfere with the chainstay if you move it to the middle position, so you'll need to figure out what you're willing to live with. Of course you could buy a new crank, but it's not necessary and you might have the same interference problem, depending on your gearing.
- If you're removing chainrings, you'll need new stack bolts to mount your 1x ring (or just washers to take up the excess bolt length); you'll also need to remove the crankset entirely to get the small ring off.
- Chain drops will be a bit of an issue. It was rarely a problem for me using my 1x conversion for street riding, but it did happen. As mentioned in the linked thread, you can mitigate this with a clutched rear derailleur, a narrow-wide chainring, or a chain watcher.
Changing to 1x7 is not going to give a very good experience. There are several features that work together to make a nice 1x setup and none of them are present in 7 speed groupsets.
1x first became mainstream with the introduction of wide range 11 speed cassettes. This allowed an adequate range of gears without the jumps between becoming uncomfortably large.
However 1x also presented problems with the chain being dropped over rough terrain. The clutch mech and narrow-wide chainring were developed to combat this.
So whilst it may be possible to convert to 1x7, it is certainly not advisable.