Chain length

bbs
bbs Posts: 5
edited October 2014 in Workshop
Just wondering my road bike is possibly running with too long chain. So with a compact 50-34 crankset when I shift to big-small the 3 chainrings aren't above each other its apparently longer with one link. Is that harmful for the chainrings? Should I buy a connector pin to make it shorter?

And one more: I'm pretty tall 197cm with an 58cm frame, 30cm seatpost and MTB shoes. That means my seatpost's "min" marking is ~10mm above the top of the seattube. Is that normal or is a really important sign?
Thank you

Comments

  • pinno
    pinno Posts: 51,807
    The rear mech will take up the slack of too long a chain. Difficult to say unless you posted a picture.

    The transmission would be smoother with the right length of chain and too long a chain can sing about increasing the wear rate but it would have to be exceptionally mong to do that.

    Pretty sure the manufacturers of the seatpin have set that mark with a large margin of safety. That's your call. Seatpins don't cost too much.
    seanoconn - gruagach craic!
  • dj58
    dj58 Posts: 2,221
    bbs wrote:
    So with a compact 50-34 crankset when I shift to big-small the 3 chainrings aren't above each other its apparently longer with one link. Is that harmful for the chainrings? Should I buy a connector pin to make it shorter?

    Can you clarify what you mean as this does not make sense? As for your seatpost if you don't have enough inserted into the seat tube you could damage the frame, sounds like you need a longer one.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    yepp, if your seatpost is not inserted to the mark which says "min insertion" then get another post. I don't reckon the frame is at risk but the post certainly is and you wouldn't want a post failure.

    Agree with the "post a piccie" remark. Not sure what your setup looks like. There are some very good online tools for chain length as well as the old school "big ring/big cog no RD and + 1 inch" rule (something like that):

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

    When in doubt, use your eyes. I have kind of settled on that as the best rule.
  • pinno
    pinno Posts: 51,807
    ^ but it says this:

    "I have no idea how the magic number of 0.0796 was derived but the formula appears to provide a pretty good approximation to the shortest possible length of 1/2 inch pitch bicycle chain that will theoretically go around the two cogs on a fixed wheel bike. "

    1/2 inch pitch!? Is this the calculation for old 5 speed chains?
    seanoconn - gruagach craic!
  • Bobbinogs
    Bobbinogs Posts: 4,841
    Yeah, I think that text just reflects the fact that they frigged the calculation to make it work. However, it does work... I have tried it a few times and it is pretty much spot on.