Do I need new chain? Going from 32T to 30T and 11-36T to 11-40T?

[drabina]

I am looking to replace my 32T chainring with 30T and also my 11-36T cassette with 11-40T. Will I have to add links to my chain to clear the 40T on the new cassette? I am asking because I may just order new chain while I am placing order for the parts.

[HerrKaLeun]

unless your chain is really new, always new chain with new sprockets.

Your existing chain may be 2 links (1") too long, or correctly sized. you need to verify how long it is based on your derailleur specs.

there are some general chain length rules about going large-large cog and leave 2 extra links (1"), however SRAM 11-speed RD require 4 (2") addl. links. RTFM

[MSU Alum]

I would also get a new chain.

[drabina]

Thanks guys. I will get a new chain.

[noapathy]

One thing you didn't mention was why you're replacing...if due to wear, I agree it's new chain time. If the parts are mostly new I wouldn't bother (just re-measure and add links as necessary).

Also, you need a chain checker. That'll answer the question better than the internet.

[drabina]

I am replacing cassette and chainring to get better radio for mountain biking. The hardware including the chain do not have more than 300 miles on them.

[Lone Rager]

You can almost certainly use the same chain. The chain basically goes halfway around the cog and chain ring. On the chainring, it will see one less tooth. On the largest cog it will see 2 more teeth. That's a total increase of 1 tooth or 1/2". You can only change chain length in 1" increments.

[noapathy]

I am replacing cassette and chainring to get better radio for mountain biking. The hardware including the chain do not have more than 300 miles on them.

Still depends...if you keep it clean and shift smooth 300 miles is no big deal. Run in the mud/grit and skip cleaning, 100 miles can kill a chain. Chain checker will tell you for certain either way.

Personally, if you don't have a spare chain I'd order one anyway. Keeping a spare around is a good thing.