Cassette / derailier compatibility and gearing

JST
JST Posts: 158
edited February 2008 in Road beginners
Another gearing question i'm afraid!!

I have just bought a used road bike with a Campag Chorus 52/39 chainset and 10 speed centaur 12-23 cassette. As someone who is newish to road bikes, whos fitness is improving and lives on the edge of Dartmoor I am going to change the cassette to get lower gearing for the hilly bits.

I'm thinking along the lines of 13-26 or 13-29. Will these work ok with the current derailier? Will the current chain then be too short with either of the above?

My hybrid I have been riding up till now has a 52/42/30 chainset with a 12-25 9 speed cassette, I very rarely use a gear below the 42/12 but then I suspect on steep hills i'm not spinning as fast as I should!

My current lowest gear (39/23) is 44.6 inches
with a 13-26 the lowest (39/26) is 39.4 inches
with a 13-29 the lowest (39/29) is 35.3 inches
on my hybrid the 42/25 is 45 inches but then I can as low as 30/25 which is 32.1 inches

Any comments and suggestions gratefully received :D

Comments

  • meagain
    meagain Posts: 2,331
    "the current derailier?"

    13-26 almost certainly; -29 maybe! The specification should be listed somewhere (well, it would be if it were Shimano, but I assume Campag) and will tell you max sprocket difference, small to big and max big.
    d.j.
    "Cancel my subscription to the resurrection."
  • JST
    JST Posts: 158
    Ah yes, the current rear derailier is a campag centaur short cage I believe. I have just had a look through their site and the blurb on the bottom of page 16 of the instruction manual here : http://www.campagnolo.com/repository/documenti/en/7225195-Rear%20derailleur-0606.pdf says all cassettes except 13-29, although this is taken from the 2008 info and I think mine is a 2006. So it looks like I should try the 13-26 for starters...
  • meagain
    meagain Posts: 2,331
    I know nowt about Campag, but will not the cranks take smaller rings (even if not down to "compact" sizes, say a 50 and a 36)?
    d.j.
    "Cancel my subscription to the resurrection."
  • JST
    JST Posts: 158
    I don't know, maybe someone else can answer that?? I can't find any info on it..
  • Steve928
    Steve928 Posts: 314
    39T is the smallest chainring possible with your chainset, assuming it's a standard Campag double with 135mm bolt circle diameter.

    A short cage derailleur handles a double chainset and 13-29 cassette fine (even a 13-30 custom cassette in fact) if you set the chain as long as possible i.e. 39T chainring + 13T sprocket and take out the minimum links to have the chain clear the jockey wheels. Your existing chain may of course be too short though.

    If the 13-26 goes low enough for you then use that, as the 13-29 really misses the 18T sprocket that gets dropped to add the 29T - in my opinion.

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