Hi, I just got a new wheel set and I am going to a 11-28 cassette from a 12-15 will I have to put a longer chain on ??? I was hoping to switch back and fourth . If I have to I'll put quick release master links and switch chains with wheels....

I go by the old standard, wrap the chain around the largest cog and the big chainring, not through the derailer. Pull it fairly tight to see where the links would match up. Now add 2 links length, or 1 plus master link if you use one.

It depends on whether your existing chain is long enough to work with the new cassette or not. For road bikes with double cranks, I generally give them as much chain as they can handle in the small-to-small combo without the RD losing tension or rubbing its cage tab on the bottom section of chain. If your chain's sized to that target with the 11-28 cassette, it will also handle your 12-25, so you might just need one new chain. With more chain, the upper pulley tends to track closer to the cassette cogs when in the big ring, where the pulley cage is more extended; that's the rationale behind using as much chain as practical. It also leaves you more breathing space for larger cassettes, and for removing damaged links if you have a mishap and need to fix it to get home.

This assumes that your old cassette isn't worn to the point where it has problems with a new chain; if that were the case, your plan of two chains dedicated to the two different cassettes might be the best compromise.

I assume you meant you were going from a 12/25. If the chain was sized as small as possible with the 25, then you need to add 3 links. It's likely there's enough excess chain totake the 28.

Put the 11-28 on the bike. Put it in the repair stand. Gently put the bike in the 53/28 combination. If there's enough chain to go into that combination comfortably, then your fine. If it's a stretch to get it in the 53/28, you need to add chain.

Even if you never cross chain into the big/big combination when actually riding, the chain needs to be long enough to accomodate that combination, under load, or bad things will eventually happen.

You may need a new chain anyway. If you do, size it to fit the 28, and you'll be fine running either the 25 or the 28.

I use the same method - learned it from a Shimano derailleur documentation, and it works like a charm.

Meant I did not need a larger-cage model, when I replaced the cranks in my bike with a triple. Adjusting it this way, the original one works fine as always, I saved money and preserve the groupo intact.