Simple chain length question

[tele]

I got a new 13-26 cassette. Will the current chain for a 12-25 fit or do I need to break out a new chain?
thanks
Kevin

[roydyates]

I got a new 13-26 cassette. Will the current chain for a 12-25 fit or do I need to break out a new chain?
thanks
Kevin
Probably, but it depends on how your chain was sized. With your 12-25 cassette, shift into the big ring up front and your biggest cog in the back. If you can nudge the rear derailleur to create some slack, then the old chain will fit fine. Of course, you ought to get a new chain when you get a new cassette.

[Louis]

For just one more tooth on the big cog? Unless you were already too short to begin with, it seems unlikely to me. Try it with the existing chain and see what happens. How far up does the R-der cage have to go? Measure with the current cassette, swap out, and see how much it changes with the new one.

Louis

[Jeff N.]

I'm thinkin' you'll probably be OK. Jeff N.

[Bob Loblaw]

Here is it in old school BASIC style.

The only time you'd be at risk is if you ride on the large chainring and largest cog on the cassette.

IF you ride on the big/big gear, THEN test it out in that gear
IF it rubs or behaves strangely, THEN don't do it.
IF you must do it AND it rubs or behaves strangely, THEN get a new chain.

BL

[Ralph]

I would try it with the old chain on the work stand to see if I needed 2 more links with the 13-26. I could break the old chain and put it back together good enough to check it on the stand. I usually keep an old chain around with some extra links for this purpose. Then I just have to cut the new chain once.

[tele]

thanks all, used a new chain anyway to do some cleaning on the other chain. used the existing chain for length and seemed to work just fine on todays ride.
thanks again