I have a 11-42 shimano cassette 10speed, need a new one but none available anywhere, can I change to any other 10 speed cassette, I'll be changing the chain at the same time, the rear mech is a long cage, will I need to keep the new cassette to a certain size to accommodate the longer cage?
If you are happy with the gear ratios you already have then you may be best to track down the same sized cassette. (ie 11-42)
You probably already know this but just in case, the higher number of teeth a cassette has, the easier it will be on the hills.
If you find yourself using the largest cog on the cassette to get up hills then you may need the larger 42t (42 teeth).
10 speed 11-36 may be more readily available.
The 11-42 cassette will more than likely have the following teeth ratios:
11, 13, 15, 18, 21, 24, 28, 32, 37, and 42t sprockets.
This means the second largest cog will have 37 teeth.
A good way to test if an 11-36 cassette would be ok for you is to go to your steepest local hill and see if you can get up it using your 2nd biggest cog (not the 42t).
This should be 37t and if you can get up the hills in the 2nd biggest cog then you should be ok.
If you feel you need to go up to the 42t (biggest cog) then you will be better tracking down the 11-42 cassette.
Hope that makes sense?
And if you already know all this then just ignore!
The only 10 speed 11-42 cassette I can find is on
ebay.
ebay link
I'm not saying to buy this..just all I could find when searching.
Some other local shops or other places might have them in stock too.