Originally Posted by
sandeept
The situation on my bike is a bit odd. The complete chainset is a 10 speed Shimano Ultegra setup, except for the cassette, which is an Ultegra 9 speed.
That's not going to work well at all. A 10-speed shifter, paired to a 10-speed derailleur, will move the chain over the exact distance from cog to cog on a 10-speed cassette.
The cogs on a 10-speed Shimano cassette are 3.95 mm apart. Cogs on a 9-speed cassette are spaced at 4.34 mm. It's not even close to matching, so shifting won't work well at all.
Originally Posted by
sandeept
I do not want to replace the cassette yet (unless you guys strongly suggest I do; it will be another expense) but need a new chain.
If you've got 10-speed shifters and derailleurs, you really need to replace the cassette. It doesn't have to be an expensive Ultegra cassette, though. Any Shimano-compatible cassette will do, so long as its gearing range doesn't exceed what your derailleurs can handle. Shimano, SRAM, Microshift, SunRace, Nashbar...
After replacing the cassette, be sure to adjust the rear derailleur.