Bicycle Mechanics - Swapping out cassettes- adjust deraileur/chain length?

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Stefan.
09-16-10, 02:49 AM
Hi there. I recently purchased a pinarello that came with "junior gearing" (14-25 I believe). I want to swap out the cassette for an 11-25. Does this require the rear deraileur to be adjusted, or to change the length of the chain. Since the highest gear remains the same, I don't think so, but just want to confirm.

Thanks all. Long time lurking, first time poster.

constant mesh
09-16-10, 04:23 AM
Chain lenght will be fine, the only RD adjustment that you will have to do is the spring screw if you have one, but usually it's a straight swap, because your lowest sprockets are the same.
thompsonpost
09-16-10, 06:06 AM
That's "B screw" adjustment you refer to.

andrewluke
09-16-10, 10:18 AM
Just remove the chain and move the derailleur by hand back and forth to see the spacing between the cogs and the guide pulley (the one closest to the cogs). Adjust by turning the B-screw. You normally want that around 5-10mm from the cogs to the pulley at its closest point depending on manufacturer (I set based on the big cog with an 11-25/28 and SRAM). It can be checked and set with the chain on but it's a lot easier without.