Hey all, I’m doing a 6 day enduro Mtb race in a month and just considering dropping a chainring size on my sram eagle drivetrain. Just want to make sure I have enough gears when I get tired after day 4 with heavy bike and carrying a bit more kit than usual. Currently running 32t up from with 12 speed 10-52 cassette. I also run 155 cranks so have a bit less leverage. Wondering if I will need to shorten chain to drop to 30t or can I just add a bit of b-tension?
For just 2 teeth, I wouldn’t change it.
B-tension’s primary job is to set the jockey wheel’s distance from the cassette; it is not a substitute for compensating for chain length. You can of course do some back-of-the-napkin math on what happens to chain length when you subtract two teeth from the chainring, keeping in mind that the chain only contacts half of these teeth at one time. But this makes a big assumption that your chain is perfectly sized right now, when it could be a little over or under. My best advice is to check chain length against the Sram manual once you have the new chainring installed. 1x-mtb-mechanical-derailleurs-user-manual.pdf
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A two tooth reduction in chainring size would require a single link removed to maintain the same pulley wheel position. You can’t remove one link from a chain, unless it’s a (confusingly named) half link chain, which it isn’t.
So, assuming your chain is not a link too long with your current chainring, leave the chain alone and go enjoy the event.
i think the difference in chain length is about 12mm so half of the amount you can adjust by. Also sram guide leads to chains that are too long in my experience on my bike. I know be tension is not there to adjust chain tension but you can tweak it a bit to get the chain taught in the hardest gear.
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But also, you can remove a link if that makes the system function better (worthwhile for an event, in my view), and then put it back with a 2nd quick link. There’s nothing wrong with running several quick links. (As a stunt, people have made entire chains out of quick links, and that works.)