I just swapped my 10 speed Ultegra cassette from the stock rear wheel that came with my bike (Shimano Ultegra WH-6600's) to a set of Mavic Ksyrium ES's. I followed all the directions on the park tool site for removal and attachment of a cassette like mine, even torqued the lockring down to the 40 Nm spec. After going for my first ride this morning on these wheels I noticed that the rear shifting is off. Looks like the rear derailleur thinks the second to largest cog is the final gear, and when I'm shifted into any of the three largest cogs the chain leaps down 1 gear. Is there a spacer or something I need to install for a 10 speed Ultegra cassette for Mavic ES's? I don't think that's necessary for this size cassette, but I could be wrong. Or is it just a matter of re-adjusting my rear derailleur by tightening the barel adjuster or messing with the limit screws? I'd hate to mess with the screws if I don't have to - the derailleur was shifting smooth as silk on this same cassette when it was attached to the Shimano wheel, and there was no spacer for that cassette on that wheel. My brifters are 10 speed Shimano Ultegras too just so you know. Any help on the easiest way for me to fix this would be greatly appreciated!