Chain cassettes

[buddiegolf]

Hi<br />
Can anyone tell me how to know what ratio means in relation to chain cassettes example 31-21 etc and how can I tell what mine is as I wish to replace it.
Thanks

[cyclerUK]

To get a new cassette you need to know:-<br />
1) Manufacturer (Shimano, Campagnolo, Sram etc,?)<br />
2) The number of sprockets (5,6,7,8,9,10 or 11)<br />
3) The ratio (count the number of teeth on the smallest sprocket, count the number of teeth on the largest sprocket ie. 12/28 )
And that's it.<br />
So as an example = Shimano, 7speed, 12/28.