[Closed] Smaller chainring, should I shorten the chain?

I've never bothered when switching between 30T & 32T. I don't know if it's optimal or not but I don't notice any poorer gear changes one way or the other.

Strictly, and assuming the chain was the correct size, yes.

Practically: probably pointless. Ride it and see if it feels overlong.

Rear mech will likely take up the slack. That's its job after all.

Unless of course you're running singlespeed, then yes, you need to shorten the chain.

Strictly, and assuming the chain was the correct size, yes.

No. Reducing the chainring size by two teeth means the chain needs to be one tooth shorter, so half a full link. You can only shorten a chain by a whole link, which is two teeth’s worth of chain, so if the chain was optimal before you could make it too short.

I'm surprised how often this gets asked.

It varies from bike to bike. If it needs shortened, shorten it!

Unless it was right on the limit of being too long before then no. As above, the change in length is less than the minimum amount you can shorten it by.

I'm surprised how often this gets asked.

It varies from bike to bike. If it needs shortened, shorten it!

You're surprised yet offer no practical advice for those that don't know whether it will likely need shortening or not, or what to look out for if it is too long.

Thanks to everyone else for their help, I will give it a go and see what happens.

I swap between a 32 and 28 without changing the chain length. No issues apart from slightly slower downshifts

Strictly, and assuming the chain was the correct size, yes.
No. Reducing the chainring size by two teeth means the chain needs to be one tooth shorter, so half a full link. You can only shorten a chain by a whole link, which is two teeth’s worth of chain, so if the chain was optimal before you could make it too short.

If we're on pedantictrackworld here, just because it's not practically possible to shorten the chain appropriately does't mean that it shouldn't ideally be shorter... 😉

Personally I'd probably not even have given it a thought going between the two, but if the person who'd initially sized the chain had got it wrong for whatever reason then it is possible that such a small change could be the straw that does it.

Being even more pedantic 2 teeth less does not equal one link. Its less than that 'cos of trigonometry

Two adjacent chainring sizes could run from one chain length. However, your 32 might run with the 30, or it might run with the 34.

However, the same chain length, while it may work with all 3 sizes, is not optimised.

I use the park chain length equation as a stat point. Remember, when it asks for chainstay length, you need the longest length, where ever it may be in the suspension travel.

Just check it at home and if the mech isn't catching the chain or frame anywhere, then it's OK.

You're surprised yet offer no practical advice for those that don't know whether it will likely need shortening or not, or what to look out for if it is too long.

Thanks to everyone else for their help, I will give it a go and see what happens.

Without seeing the bike it's not known if it needs shortened.

If the chain is much too long the mech will not be able to take the slack in the bottom gear.

Wasn't meant as a pop. Your set up might have it that it's on the upper or lower limit.

If you posted a couple of photos showing the mech position in top and bottom sprocket it would be handy. Of course if it's a full suspension that makes it trickier still, then I'd be asking you to show it at full travel.

Sram 11 was designed to work +/- 2t on the chainring without shortening the chain so it should be good for a 32 as normal and swap to a 30 or 34 without altering anything unless you were aggressive on your initial shortening.

I’ve always found the Park Tools YouTube video to be a good guide.
As others have said, if the chain length was correct for a 32T then it will probably be okay with a 30T.

My CX bike is 2x11.

Today I road around the bleak fenland countryside, occasionally changing into the granny ring for the hills (yes, there are a few).

I didn't stop and shorten the chain, I just rode it.

It was fine(*).

(*) Ignoring the lunatic car drivers and the grey countryside. Coffee was nice.

I use the usual method of big:big, as tight as possible plus one link.

I've just set up my first 1*11, is that still the correct method considering that is now a regularly used gear rather than a horribly crossed chain line that any sensible rider would only select by mistake?

I think I added two links this time but didn't give it much thought, not ridden the bike in anger yet as I'm ill 🙁

Spooky - should be ok if it shifted properly on the workstand / upside down on the floor.

One note: My experience of gx 11 is that the b-screw position and corresponding Jockey wheel offset from the cassette is quite critical for good shifting so if the chain was too tight to the extent that it wasn't possible to set this properly then that could be a problem.

FWIW I've swapped between a 32,30 and 32 oval without adjusting the chain length.