magic ratio gearing

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  • magic ratio gearing
  • Premier Icon oxym0r0n
    Subscriber

    How long have you been riding “magic ratio” for?

    Shirley the chain will wear and then you can get rid of the half link??

    Premier Icon nickjb
    Subscriber

    Mine only lasted a few weeks before it started slipping. Went with tensioner after that.

    yesiamtom
    Member

    I wouldn’t bother with a magic ratio personally….horizontal ends are so much superior. I tried it before and it worked for about 5 miles 🙁

    thepodge
    Member

    Ps, interested in answers to my question not reasons why magic ratio is rubbish

    thepodge
    Member

    Murray, thats a clever calculator but gives variants on the cs length not chain length

    smiffy
    Member

    it is not the ratio that is magic.

    thepodge
    Member

    Less pointless answers please

    amedias
    Member

    what smiffy and the link are trying to tell you is that it is not *just* ratio you need to take into account.

    it’s a combination of chainstay length, chainring diameter/teeth, cog diameter/teeth and chainstretch/wear that is used to work it out.

    We lack the required information to advise you with a single line answer, but you can work it out for yourself using the calculator in the link once you have the other bits of info.

    Murray, thats a clever calculator but gives variants on the cs length not chain length

    it shows both, the chainstay length is across the horizontal axis, the points plotted are colour coded to specific chain lengths. The vertical axis gives you the value of gear inches for the chosen options.

    making some reasonable assumptions about your chainstay length if you are currently running 32×18, and with a new chain your *might* have some success with 33×19 or 35×21, others may work once chain worn slightly.

    but both of those are going to be awkward to get rings for and I’m using assumptions, which is never a good thing 🙂

    also – half link chains are easy and cheap to get online if none available locally and the extra weight is naff all really on the whole of the bike.

    thepodge
    Member

    If I’m running 32:18 and it falls exactly on half a link with vertical dropouts, what will give me roughly the same ratio so that it falls on a full link?

    I run a bmx half link chain on the fixie and the SS but they are too big and heavy for my trail bike & don’t fit through the chain cleaner. I’ve also bought Sheffield’s entire supply of single half links so to save faff all round I’d prefer to run a whole link chain but can’t get my head round it.

    Thanks

    thepodge
    Member

    The chainstay is a constant in the equation so I assumed right or wrong that as it currently works on half a link it was an easy calculation to work on a full link. It seems as though it isn’t.

    Another reason for not using a half link chain is they seem to be predominantly 1/8 and I’m running an alfine which is designed for 3/32.

    The 33:19 is a ratio that I also though might work giving me an ever so slightly lower gearing.

    amedias
    Member

    the chainstay length is constant, but you didn’t give it to us and if you think about it, it’s not just chainlength and chainstay length that are at play, eg, adding a single tooth on a cog increases the chain length requirement but half a link + whatever increase is also needed overall to incorporate the increased diameter of the cog now it has another tooth.

    so its not as straight forward as it initially seems, we’re dealing with multiple changes even when varying only one parameter.

    throw chain wear into the mix as well and it gets more complicated again.

    Measure the chainstay length, plug it in to the calculator, and see what ratio is similar to your present one. It’s not rocket science.

    thepodge
    Member

    Good point. I really shouldn’t be trying to work this out after a ten and a half hour day

    thepodge
    Member

    That was more aimed at amedias, I’ve got some SS sprockets both above and below 18 so I might do a bit of experimenting too.

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