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Carbon Frame Flex

hebblewhitehebblewhite Posts: 3
edited April 2009 in Workshop
Hello,

I have just built up a carbon road frame after using aluminium for years and I have a quick question, when clamping in my back wheel there is a gap of about 5 - 6mm that pulls up when I do up the QR which is fine… or is it?? Am I silly to be worrying about frame failure, I know a 5 - 6 mm gap would be fine on aluminium frame but is it just as fine on Carbon?? I’ve heard they really don’t like much pressure??

Cheers guys

Mike

Posts

  • Monty DogMonty Dog Posts: 20,614
    Might be worth measuring the internal dimension on the frame inside of the rear drop-outs - it should be 130mm +/-. Whilst this level of flex should be OK for the frame - check that the rear wheel alignment is OK - it should be central in the frame and aligned front-to-back - if not it could cause you handling problems.
    Make mine an Italian, with Campagnolo on the side..
  • I think I am feeling a littel "Crabbing" or something in training! Doesn't feel 100% correct.

    If it is out of line should I use washers or something to try and bring it back in?? I think it's causing problems, abnormal sounding rub on the inside of my outer ring when in the lowest sprocket for example!?

    What do you guys recommend?? When the wheel was sat back in its natural position the wheel was rubbing on the inside of the frame so I had to re adjsut the situe of the wheel slightly to get in to stop rubbing?

    Something feel out though!!?
  • Monty DogMonty Dog Posts: 20,614
    If the rear wheel isn't sitting straight i.e. close to the chainstay, then it sounds as though the frame rear triangle is out of alignment. With the wheels fitted and standing from behind, are the wheels aligned? A long straight edge, piece of wood or kerb helps - if it isn't suggest you take it to your LBS and check the frame for alignment for a second opinion. I contact the seller if you have a problem.
    Make mine an Italian, with Campagnolo on the side..
  • pliptrotpliptrot Posts: 582
    MD, in a recent post you suggested that a take up of this magntiude was OK for a steel frame but not for any other material. Subjectivity seems to be the order of the day.

    Flexing a frame that much whatever material it's made of ain't good - either the frame's a dud, the hub is an old 126mm version, or something else in the world of continuous, delberate obsolesence is making this a problem.

    Ask again tomorrow - the oracle may give you another answer.
  • crankycrankcrankycrank Posts: 1,830
    4-6mm is too much. Either the axle is not spaced properly or the frame is not right. As mentioned the dropouts and axle spacing should measure 129-131mm. You may be OK with a larger gap but it does put more of a strain on the frame tubes and axle.
  • Ash_Ash_ Posts: 385
    Out of interest, what frame is it hebblewhite? What wheels?

    Some frames do have asymmetric stays, which might alter your perception of the situation. Carbon doesn't have the 'spring' steel does though so it certainly shouldn't need, or be able to tolerate, manipulating to get the wheel in.

    Any chance of posting a pic.? Although, I'd say that it needs to go back to where it came, regardless of what anyone on here suggests...
  • Monty DogMonty Dog Posts: 20,614
    IMO there's a big difference between what's acceptable for a new carbon frame and making and old frame rideable - I wouldn't think it untoward of running a 120mm hub in a 126mm steel frame - or fitting a couple of washers either side and experience is that it works OK - steel and titanium as used on bikes are inherently more flexible than carbon and aluminium. Modern manufacturing processes and techniques generally mean improved tolerances, a carbon frame being out of whack is more unusal that a brazed steel frame and they don't tolerate scaffolding bar techniques if they need re-jigging!
    Make mine an Italian, with Campagnolo on the side..
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