My bike is an Elswick 700c Equipe. It has a 13 - 28 compact cassette, 42 - 52 one piece chainset and 7 speed sis gears. I would like to change the chainset to a 36 - 46. I am confused as to why most of the chainsets are sold as a 7,8,9 or 10 speed etc. If I was to buy a 7 speed compact chainset, does that mean I can retain my existing bottom bracket and all will be well ? Can I buy any double compact chainset and ask which bottom bracket is needed to suit ? I need to know what my options are. Would be glad of any help to solve my confusion.