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BonkonFleet 04-03-20 10:13 AM

New cassette question
If I change from 11-28 to an 11-30 ultegra cassette will I need a new chain as well or will my current one fit?. The reason I ask is I'm getting some new wheels and I figure this is a good time to change my cassette as well and since I live in a rather hilly area and enjoy climbing I thought I'd give an 11-30 a go. According to shimano my short cage RD will support a cassette up to an 11-30. Apart from possibly needing a new chain are there any other adjustments to the RD I'd need to make?

dsbrantjr 04-03-20 10:38 AM

Whether of not your current chain will fit depends on how much, if any, extra length it has. New cassettes may not always play well with old chains. I always replace my chain when I put on a new cassette and keep them as a set; you might consider doing this with your old wheel/cassette/chain. If you decide to try and use your old chain, you must put your chain on the largest chainring and GENTLY try to shift into your biggest rear cog while turning the rank by hand, and STOP if the derailleur is stretched out straight or there are any other signs of a too-short chain.

Unca_Sam 04-03-20 10:50 AM

dsbrantjr gives great advice, your best option is to get a new chain. If your chain is 'stretched' it will quickly wear your new cassette.
If you measured your chain stretch and it's satisfactory, just use the chain sizing method Mr. Jones shows in this video.
You'll get the same information you would get from dsbrantjr's method without risking damage to your derailleur.

Unca_Sam 04-03-20 10:54 AM

Your derailleur limits might need to be tweaked a tiny bit for best performance. A TINY bit. Shimano tolerances are pretty good, but no one's perfect.

base2 04-03-20 11:05 AM

Your small/small combination is the same with new/old. After that it is a matter of derailleur capacity. Long cage Ultegra should still be within limits. If you are using medium cage it is beyond limits, but only because the limit is the 28 tooth cog. It'll still run fine on a 30 tooth cog.

If you have a medium cage and want to go beyond 30 teeth, you may want to consider the long cage.

...And the advice to change the chain when doing cassettes is pretty solid. The more worn the stronger that advice is. If all is new-ish (less than 500 miles) I wouldn't be too concerned though.

Bill Kapaun 04-03-20 11:07 AM

Put the chain on the largest cog & ring and see how much excess chain you have.
IF you have at least three 1/2 links, you are good. (1-1/2")
Each 2 teeth > cog will require 1/2" more chain.
You want at least 1" of "slack"

dsbrantjr 04-03-20 12:46 PM

Originally Posted by Unca_Sam (Post 21398740)
Your derailleur limits might need to be tweaked a tiny bit for best performance. A TINY bit. Shimano tolerances are pretty good, but no one's perfect.

Expect minor limit and indexing adjustment, even when replacing like with like. You may (probably) need to adjust the B screw for the larger big cog.

BonkonFleet 04-03-20 12:56 PM

Wow thanks for all the great answers. Normally I would just change the chain no questions asked but in this case I had just replaced it last summer and it probably has 1,000 miles on it or so. I think I will just change it to be safe and let the LBS deal with any RD adjustments that need to be made.

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