Hi y'all. I'm struggling to get up the Fife hills with my city bike so it's putting me off cycling to work - in the granny ring I have to leave my seat - something I'm not confident doing with a dodgy knee, and it is still really hard. I've done the same hill on my homeward route on both my MTB and tourer in the granny rings, and whilst hard, have managed to stay in the saddle.

So looking at my rear cogs on the city bike I have 12 on the small ring and 25 on the big ring, whereas my MTB has 11 and 34. So I'm presuming the bigger the ring (34 as opposed to 25) the easier the gear? Is this right? If so I'd like to change the cogs but am clueless. Will my chain still fit? What is the difference between a cassette and a freewheel? How do you go about swapping them over. I've seen this

http://www.wiggle.co.uk/ProductDetail.aspx?Cat=cycle&ProdID=4000000046&N=Shimano%20HG50%207%20Speed%20Cassette

at Wiggle and wonder whether it would be suitable. Trying to save money I'd like to have a go myself.

If you're going to change the rear cassette / freewheel you need a chain whip (sounds dodgey but it's a piece of chain attached to a spanner handle) and a spanner.  You would also need to check if your rear hub can accomodate the new cassette. When you change the front or rear sprockets / chainrings it's best to change your chain to prevent wear.

Hope that helps, good luck

hey,

this should help

http://www.parktool.com/repair/readhowto.asp?id=48

 kate

Thanks everyone, it's a bit clearer now but didn't realise there are so many different types and it looks a bit fiddly for someone with little patience . Also the 7 speed cassette I wanted is unsuitable as I currently have 8 on the rear , glad to know it counts.

The Parktool link is very helpful Kate, thanks. Think I saw the 'chain whip' in the photos.  I'll have a good read and cost everything up including the tools to see whether it's worth my while - might end up taking it to the bike shop but it would be nice to have a go myself.