Chain length?

TMR
TMR Posts: 3,986
edited May 2012 in Workshop
Just changed the cassette on my rear wheel from an 11-25 to an 11-28. How much longer does the chain need to be to accommodate the 28 tooth? The rear dérailleur is too far forward for my liking.

Have a new chain to put on, it's just an 'interest' question more than anything.

Comments

  • arlowood
    arlowood Posts: 2,561
    Hi there

    FWIW I have just swapped my 11-28 cassette for a 12-30 and stuck with my existing chain just to see if it would be OK.

    Turns out that I have managed to get away with it without any need to lengthen the chain or fiddle with the rear mech adjustments.

    However it will probably depend on how short your chain was to begin with. Try this calculator to see if you need to add any links.

    http://www.epicidiot.com/sports/chain_l ... tm#results
  • rpd_steve
    rpd_steve Posts: 361
    Always run with your chain as long as possible - it reduces wear (by a ridiculously small amount) and the reduced tension will improve derailleur function. Set is so in your small/small combo the chain almost touches the upper jockey wheel.
    If it is then too tight in the big/big then you need a longer cage rear mech - but most are good for 27/28T.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    mmm, not sure about that chain length calculator from Arlowood. Try this one as it works well (you just need to measure your chain stay length (centre of BB to back axle) and then stick in the chain ring and big cog values):

    http://www.machinehead-software.co.uk/b ... hcalc.html

    The old fashioned way is to miss out the derailleur and wrap around the big ring/cog, and add a link (or two):

    http://sheldonbrown.com/derailer-adjustment.html#chain
  • Tabiliran
    Tabiliran Posts: 22
    Hello there. I have some questions regarding chain line/drive- I'm not really sure of the term. Anyway,allow me to describe my query. I've noticed that during the downward stroke of my right crank my chain line tends to go towards the right side of front derauiler cage. I'm not particularly sure whether this is mechanically normal or some problem with bottom bracket.

    I'm hoping that you have some patience for some ignorant cyclist like me.

    Thanks.

    Rolly
  • sungod
    sungod Posts: 16,861
    Tabiliran wrote:
    Hello there. I have some questions regarding chain line/drive- I'm not really sure of the term. Anyway,allow me to describe my query. I've noticed that during the downward stroke of my right crank my chain line tends to go towards the right side of front derauiler cage. I'm not particularly sure whether this is mechanically normal or some problem with bottom bracket.

    frame/bb/crankset will have a bit of flex, some are flexier than others, so it may be simply that

    see if there's any play side-side in the bb, or if the cranks are slightly loose on the bb spindle, or if there's roughness in the bearings, if you find any of these then get it checked
    my bike - faster than god's and twice as shiny
  • Pheckfairy
    Pheckfairy Posts: 12
    Campagnolo recommended way is to place chain on smallest gear combo. Ideal chain length will give 10 to 15mm clearance between chain and rear mech arm. Seems to work well on my bikes.