I am gonna change the cassette on my winter bike which carries a complete Tiagra groupset. Nice enough, all thing considered but a bit long in the tooth. The 105 / Ultegra 10 speed cassettes are well priced at the minute so I am going to go for one of them. Can anyone see a problem going for the 105 / Ultegra cassette and taking out the Tiagra cassette. Something in my mind says that the chain may have to go as well.