New 8 speed rear cassette, does it exist?

broona
broona Posts: 414
edited September 2012 in Road buying advice
Riding Shimano 2300 8 speed compact 50/34 up front, 11-28 out back, and potentially looking to change to a 30/32 on the back if possible, and if a suitable cassette exists.

Mostly ride a MTB, but trying to get into road biking too, and struggling a little with the gearing on some of the steeper climbs, easy in 27x36t (just checked, thought it was only a 34 on the rear!) on my MTB, not so easy in 34x28t on my road bike!

Is there such a thing as an 8 speed 11-30 or 11-32 cassette, and would it fit my current setup, or would I need a new rear derailleur?

Comments

  • getprg
    getprg Posts: 245
    Try reading this

    http://techdocs.shimano.com/media/techdocs/content/cycle/SI/2300/SI_5XA0A_001/SI-5XA0A-001-ENG_v1_m56577569830673817.pdf

    Assuming you have the RD2300 rear derailleur - according to this the maximum sized rear sprocket is 26 teeth with a max combined capacity ie tooth difference of 35. Your chainwheel difference is 50-34 = 16 and rear cassette difference is 28-11 = 17 making 33 in total.

    So you are currently not using the total capacity of the rear derailleur even with a 28 tooth sprocket but according to shimano you shouldn't be able to run a 28 sprocket - only a 26. Shimano usually err on the cautious side with capcity specs.

    The main problem going bigger than 28 (say a 30) would be the possibility that the top jockey wheel (with chain) will foul on the largest rear sprocket. There is some adjustment in the rear derailleur to over come this but, of course, this has a limit. The only way to find out is to try a larger cassette.
  • getprg
    getprg Posts: 245
    So far as larger 8 speed cassettes are concerned they do exist - you can use 8 speed MTB cassettes as these are interchangeable on road freewheels.
  • giant_man
    giant_man Posts: 6,878
    I got a new one a couple of years ago for my shimano winter jalopy, so yes they do exist .....
  • broona
    broona Posts: 414
    Thanks for the replies, I'll take a look at some MTB cassettes then, if I buy one and it doesn't fit/work, at least I can just sell it on. Thanks again. :)