Conversion to 9 speed
Hi, I have an off the shelf Specialized Allez with 8 speed rear cassette. I have Sora 8 speed shifters. The rear derailleur is 9 speed Tiagra. What's to stop me smacking a 9 speed cassette on in place of the 8 speed? Or am I going to need to change the chain/front mech/chainset/shifters? I don't know exactly how the shifters work but they aren't indexed they shouldn't be a problem should they? I realise a narrower chain might have to be fitted, but then how would that affect the front chainset?