We use #25 for everything. As long as you run it/tension it properly, there is no conceivable way you could break it. Please note I'm not saying it's invincible, I'm saying when done correctly, it is more than strong enough.


As for tensioners, that depends on your drivetrain setup. Some teams buy idler sprockets from McMaster, or some equivalent, and then put it on a U bolt so it's adjustable. I personally prefer to go with live Axles, and pull bearing blocks. But that requires more machining and materials.

Good luck! Post some pictures once you finish it, so we can see!