I’m running a 3×9 setup with an XT rear mech, my newly bought sram chain is massively long!

I don’t have the original chain to measure and use as a guide.

How do I figure out how long the chain should be?

Do I put it in the biggest chainiring and the biggest rear sprocket and just wing it seeing as that’s the longest the chain is going to need to be – I know I shouldn’t run it like that though.

Cheers
Col

Thread chain through mechs etc
Put chain on largest sprocket and largest chainring.
Pull as tight as the mech will allow it
Trim to nearest link

Done. 🙂

I put it on the smallest sprockets both front & back and remove enough links to pull the derailleur from the default sprung position

Does that make sense?

One rule of thumb I read (possibly in the shimano docs) is wrap chain round big cog, big chain ring, but not through the rear mech. Add two links for a hard tail or four for a full sus.

Both make sense to me 🙂

As per pete poddy above but don’t pull so tight as to make the chain take a straight line through the jockey wheels. There should still be a slight kink through the mech.

In addition, if it’s a full suss bike deflate the rear shock and do the above measurement with the rear end fully compressed.

big ring to big ring plus 2 links

It depends on your setup. For most triples I would go big ring to big ring without going through the mechs, no overlap except the powerlink.

For one of my doubles it’s big ring to big ring plus one plus the powerlink, (full sus) but for the 2×9 HT it’s big to big, minus one plus the powerlink. I found even then, that with a med cage mech and Blackspire the rear mech was folding back on itself on 11-22, and had only a wee bit of an S shape in big-big (36-34)

Trial and error I’m afraid. B screw adjustment became critical on my setup.

As per pete poddy above but don’t pull so tight as to make the chain take a straight line through the jockey wheels. There should still be a slight kink through the mech.

In addition, if it’s a full suss bike deflate the rear shock and do the above measurement with the rear end fully compressed.

Tick.. you wouldn’t want to tear off your mech as you g-out the bike as you’re tearing down the hill typing to beat your mates strava! Particularly important in 1x or 2x.. in 3x.. you should never be in that gear, but stranger things happen.