fixie chainline

adedownunder
adedownunder Posts: 30
edited February 2010 in Workshop
Hi guy's

Im in the process of building my first fix wheel bike and was hoping someone could help with a problem i have?
I have fitted most of the bike including the chainset, on placing the rear wheel in the drop outs and getting a straight line it looks as though the chainline is around 4mm out, being new to this type of build i need to know is this amount (4mm) aceptable? if not can i get shims or spacers to bring the cog out a bit or will i need a new hub axle or hub to allow for the change, hope this makes sense!!
Hope you can help!!

Ade

Comments

  • Monty Dog
    Monty Dog Posts: 20,614
    Anything more than a couple of mm is going to be problematic as the chain centreline is outside of the chainring centreline - you need to keep the chain tension high to compensate and it'll still be noisy and rough. Depends on whether it is the sprocket or chainring that is too far out - some sprockets are assymetric, so turning it around may gain a mm or so, fitting a spacer behind the driveside BB cup - to move it outboard, or as you say fitting a longer BB - depends on your BB/crank combo. You could also adjust / respace the hub on the axle - this will also require a redish of the wheel.
    Make mine an Italian, with Campagnolo on the side..
  • FBinNY
    FBinNY Posts: 1
    adedownunder wrote:
    Hi guy's

    .... it looks as though the chainline is around 4mm out, being new to this type of build i need to know is this amount (4mm) aceptable? if not can i get shims or spacers to bring the cog out a bit ...

    Don't respace the sprocket. Obviously perfect chainline is ideal, but 4mm isn't a meaningful error. 4mm is less than 1° off or, put another way, equivalent to being one sprocket over on a derailleur bike.

    If your BB system uses spacers, switch 2 around to improve things if you wish, but don't add a spacer behind the sprocket. That'll reduce the thread engagement, which is probably more of a problem than the chainline error.

    BTW- If you're riding a fixed gear, I hope you're using a track hub, with a reverse threaded lockring, or have 2 brakes on the bike. If you're riding a SS freewheel it's fine to use a road hub, and in that case might add the spacer if there's sufficient thread available

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