Chain Length- Different Cog Ratios
 

If I change replace my existing cassette that is 14/28 with one that is 12/28 how many or do I need to take links out of my chain???

Or just re-adjust my limit screws?

If your chain is the correct length now and the new cassette is the same number of gears, you don't need to change anything.

Remove the chain from the rear derailleur cage and wrap it around the biggest front and rear sprockets. Then see where you'd have to join it, and add two links to it.

This is typically how Shimano and others tell you to do it in their installation manuals.

If the old chain did work before with no issues, then as [MENTION=35181]Reynolds[/MENTION] said, you don't need to change anything. Just use the same length the old was.

Nothing needs to change.

Just bolt on the new cassette and ride.

You have exactly the same size large cog as before, so of course the chain length needs to stay the same. Even if you had gone to a 12-24 there's no requirement that you shorten the chain. If your large chainwheel is 52 it is not a great idea to go down to 12 teeth unless you are planning a lot of downhill pedaling (which itself is pretty wasteful).

That's not what limit screws are for. They restrict how far the derailleur can move, so the chain doesn't come off the small cog or let the derailleur go too far toward the spokes. If the derailleur cage catches on a spoke, the derailleur will be ripped off the bike, causing serious damage.

If a chain is too long, then the small chainring - small cog combination will have the derailleur arm fold all the way up, and the bottom portion of the chain will rub on the top pulley chain wrap -- annoying but not serious.

If the chain is too short, it can jam when in the big chainring and attempting to shift to the biggest cog. Serious.

Here is a useful manual. Page 8 and 9:

http://si.shimano.com/pdfs/dm/DM-RD0003-08-ENG.pdf

All the above is what I needed. I thank you all. (I saved the Shimano manual.)

I'm good to go...........

I'm a believer in the big/big method for determining chain length. If your chain is too short, accidentally shifting into the big/big can cause a bunch of damage to your bike in less time than it took me to type this. In your example, neither the big chainring nor biggest cassette cog has changed so, assuming the chain was right previously, it'll still be right.

On the other hand. Chains and cassette (or freewheel) cogs tend to wear together. An old chain will wear new cassette cogs prematurely. I don't always change cassettes when I replace the chain but I always install a fresh chain with a new cassette.