Chain Sizes

[JoniL]

Hi,
I'm not sure if I have the right idea of chain sizes. I have a mountain bike that is in dire need of a new chain, I'm just not sure which one to buy. It's got 3 front chainrings and a 7-speed freewheel. I also have a road bike which is a double, with an 8-speed cassette. I was told that you just add the number of chainrings you have on your bike, so does that mean both would need a 10-speed chain?
Thanks,
Joni

 

[Zoiders]

I won't give a lengthy answer and quote exact sizes, some one will and it will confuse.

Chains get narrower the more sprockets you have on the block at the back.

You need a chain to fit a 7 or 8 speed indexed system, the chain is the same on both, ask for that in the LBS and they will give you the right one.

 

[HLaB]

6-7&8 speed chains are the same thickness; you only need a cheaper 8sp. 9, 10 & 11 all narrower however but that needn't concern you.
If the chain was badly worn you may need to fork out for a new cassette too.