cycling newbie after some advice

[gkirky]

Hello all,
my names george, this is my first post on the website, wasnt sure weather to put it in beginners or mechanics so im sorry if its in the wrong place. i started riding on and off road about a month ago and really enjoyed it, the only problem was my bike, i mean it was a cheap-as-chips car boot jobby and i dont mind admitting it is sh*t haha! as i enjoyed riding i though an upgrade was in order, though being a student unfortunatly money is lacking. i have bought myself a kona blast ( not sure of age as i bought it on eBay) and it seems perfect for me, although i want it to be reliable so i would like to replace some of the parts that are looking worn.
firstly the chain slips occasionally, so i thought it would be best to replace the chain, front and back sprocket (or would it be easier to just buy a new rear wheel and front sprocket??)
i have had a look online for these, but it seem i need a little more bike knowledge before i buy the wrong parts. currently i have 21 ( 3X7 ) gears on my bike, so would i be right in thinking i need a 7 speed bike chain? and also does it matter what chain i buy, as i can see they vary in price?
With the back sprocket (or do you call it a cassette?!) im assuming i would need a 7 speed again..? had a quick look on halfrauds website and i dont really know what the 12 - 28T means but would i need something like this?

http://www.halfords.com/cycling/bik...ables/shimano-cs-hg20-7-speed-cassette-12-28t

(i know this is a very cheap one, and i would rather get one thats a bit more expensive and will last longer, this is just an example)

ill leave it there for now as im asking a lot of questions and could probably do with something to read before i go much further, well thanks for reading and hopefully ill get a few replies,
george

 

[RichardB]

If your chain is slipping, it's highly likely that it and the sprockets are worn. Have a look at the teeth on the front sprocket, as they are the least likely to be worn out, and you may get away without replacing that. Nice, even teeth, good - worn, pointed or hooked teeth, bad. You need a 7 speed chain, and unless you are doing serious mileage I would think that a cheap one will do for the time being. The numbers on the sprockets are the number of teeth, so the one you refer to has a small sprocket with 12 teeth and a large one with 28 teeth - a reasonably wide range. However, different makers have different methods of fitting to the freehub, and different tools to remove the cassette. Before you spend any money, I would be tempted to take the bike into Halfords (or, even better, your local bike shop) and ask them what they think. They could swap the bits over for you for a few pence, or even free - it isn't a big job. With a new chain and sprockets, it will feel like a different bike.

Also, with a new chain and sprockets, you might need the gears tweaking so they change properly. Again, a few moments' work for a bike shop, which they may do for nothing if you have bought the parts there.

 

[Nigelnaturist]

7sp come in two varieties freehubs the cassettes you mention or a freewheel screw on, as @RichardB says it worth getting it check so you know which one (8sp can be had as freewheels as well, but much less common)