Using different Cassettes?

Rotatinglegs Posts: 7
edited June 2013 in Workshop
Hi there,

I have a 10spd Shimano mixed 105/Ultegra chainset and I have a set of wheels with a 9spd cassette that I'd like to use for racing (I am already using the original 10spd on another pair of wheels) so it it possible that I can use the 9spd cassette with the current chainset? Will I have dodgy indexing? Should I stick to the 10spd cassette and buy another one for the other set of wheels?