My current ride has a 12-26 9-speed Sram Cassette. I'm changing it to a 13-30 Custom (shimano) Cassette. Am I going to need to add links to my 9-speed Shimano 105 chain to accommodate the extra teeth? And, will the RD need reset up for the new cassette??

Thanks

Which bike?

Trek 2100 with 39/53 crank.

It is good practice to replace the chain whenever you replace the cassette. A worn chain will create abnormal wear to a new cassette.

You might need a long RD?
https://www.trekbikes.com/us/en/bikes/2005/archive/2100

He needs a chain wrap capacity of 30, the Shimano short cage rear derailleur is rated at 29. However, the Shimano ratings have a safety margin, he should be OK with his current Derailleur.

I got the new cassette from Sheldon Brown and they claim it will work with the short cage RD Shimano due to the conservative ratings that Shimano uses.

It should arrive today or Monday.

Hope it works...............

As far as having to readjust the RD; most likely you'll need to adjust the "B" adjuster. The H and L stops should be okay. You'll need to lengthen the chain, so it might be a good idea to replace it at this time. I have a 2005 Trek 2100 too. It's been pretty good except that the rear Race wheel rim cracked. Trek replaced it, no questions asked. Everything else has been perfect.

OP says the RD will arrive on Monday (RD and cassette). If you're just putting the RD on the bike you'll need to adjust the H and L stops, the B screw and the cable tension. Park Tools and Sheldon Brown have excellent directions (same for figuring out chain length.)

There isn't any new RD, just the new cassette. And it did arrive today. I've already put it on the wheel. I did also go out and get a new chain. I'm trying it without any extra links, but I think it may need one extra link. I'll check it some more tomorrow.

Thanks

Well, after experimentation I added two links to my chain and it works much better. The indicator? Before adding the links, when adjusting things and I would be on the Large/large cogs (just for testing) the RD was stretched out straight and almost touching the cassette.

Adding links wasn't that easy. I got it to work, but I'm a tad worried about it. When the pin was inserted ALL the way the link was stiff -- as in barely moves -- but if the pin is out about .25 mm the link moves normally. The pin is about 99.9% seated, but sticks out just a hair. I'm trying not to be anal about it. I don't want that to be the proverbial "weak link" in my chain.

Oh, and I learned one other thing -- don't use a YouTube video for adjusting the FD on a MTB as your lesson for adjusting your FD on a road bike. The inner and outer limit screws are reversed.