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Torsion in my frame? Is this bad?

fuzzynavelfuzzynavel Posts: 718
edited November 2008 in Road beginners
When I put on my front and back brakes and push down on one of the pedals the pedal on the other side moves....Not turning around the crank before you say it....but it looks like my bottom bracket is twisting. Could this be a manufacturing fault?
It's a Giant SCr 1.5 Btw
17 Stone down to 12.5 now raring to get back on the bike!

Posts

  • John.TJohn.T Posts: 3,698
    It's the chain stretching, the chainstay compressing and mostly the wheel flexing.
  • topdudetopdude Posts: 1,557
    Add to that, rear spokes flexing, tyres deforming, frame twisting, brake calipers deforming, etc, etc :wink:
    He is not the messiah, he is a very naughty boy !!
  • Its just the frame flexing - its a cheap low end bike, so to be expected.
  • blackhands wrote:
    Its just the frame flexing - its a cheap low end bike, so to be expected.

    I'm so sorry that I can't afford to censored 3 grand on a new bike but I still expect a quality product for the £650 RRP of the bike. My £299 mountain bike has lasted 13 years with no maintenance and I never noticed anything like this before.

    I think I'll take it to the LBS just to make sure
    17 Stone down to 12.5 now raring to get back on the bike!
  • gkerr4gkerr4 Posts: 3,408
    fuzzynavel wrote:
    blackhands wrote:
    Its just the frame flexing - its a cheap low end bike, so to be expected.

    I'm so sorry that I can't afford to censored 3 grand on a new bike but I still expect a quality product for the £650 RRP of the bike. My £299 mountain bike has lasted 13 years with no maintenance and I never noticed anything like this before.

    I think I'll take it to the LBS just to make sure

    he is right though - it is just the frame flexing - there is a reason why £2000+ carbon frames are £2000+ - they don't flex.

    My trek Pilot1.2 does it. my specialized langster does it, my S-Works Roubaix does not.
  • Thanks for all your help. I guess I am just worried that I will be powering up a hill and the flexing will lead to fractures and I will end up ripping my bottom bracket out of the frame leading to a catastrophic crash. I don't really fancy bursting a testicle on my top tube as my bottom bracket gives way :shock:
    17 Stone down to 12.5 now raring to get back on the bike!
  • topdudetopdude Posts: 1,557
    I don't really fancy bursting a testicle on my top tube as my bottom bracket gives way Shocked
    Don't worry, the top tube will probably bend and absorb the impact of your testicle :wink:
    He is not the messiah, he is a very naughty boy !!
  • gkerr4gkerr4 Posts: 3,408
    fuzzynavel wrote:
    Thanks for all your help. I guess I am just worried that I will be powering up a hill and the flexing will lead to fractures and I will end up ripping my bottom bracket out of the frame leading to a catastrophic crash. I don't really fancy bursting a testicle on my top tube as my bottom bracket gives way :shock:

    the exercise you are doing shows the flexing at it's worst - I always think that turbo trainers show the worst in frame flexibility too - it won't get any worse while you are out riding and certainly won't rip your bottom bracket out or destroy anything.

    you are using effort to deflect the frame though - which is again why people will pay for the stiffness of a top-end frame.
  • John.TJohn.T Posts: 3,698
    Which way is the bike flexing. Is the pedal moving from side to side (lateraly) or in the direction of rotation. If the former then it is frame and wheel flex. As has been said the more you pay the less of this you get. If it is the latter then most of the flex will be in the Wheel and brakes. Quite normal but again you get what you pay for.
    You probably did not notice any flex on your MTB because you never looked and also it was built like a tank.
  • John.T wrote:
    Which way is the bike flexing. Is the pedal moving from side to side (lateraly) or in the direction of rotation. If the former then it is frame and wheel flex. As has been said the more you pay the less of this you get. If it is the latter then most of the flex will be in the Wheel and brakes. Quite normal but again you get what you pay for.
    You probably did not notice any flex on your MTB because you never looked and also it was built like a tank.

    I sat on the bike and looked directly down to the bottom bracket aligning it with the top tube. It moves laterally...it is not a loose bottom bracket as that is why my mountain bike is currently dead. It spilled its ball bearings all over the road on a hill while I was mashing a big gear...It was steel and not exactly lightweight so probably no flexing in that one!

    If this is a common observation at this price point then I shall stop worrying and get on with enjoying riding. Thanks again.
    17 Stone down to 12.5 now raring to get back on the bike!
  • My original comment wasn't meant as a put down - sorry if it was a bit terse.

    Just examine all the tubes around the bottom bracket - and especially the welds - to make doubly sure that you don't have a damaged frame.
  • Brian BBrian B Posts: 2,071
    I would pop into Bicycle Works at Argyle Place up at the Meadows and let them observe the flex - they are a good LBSin your area.

    Its probably nothing to worry about but it wont hurt to get a professional opinion to put your mind at rest.
    Brian B.
  • dennisndennisn Posts: 10,601
    fuzzynavel wrote:
    Thanks for all your help. I guess I am just worried that I will be powering up a hill and the flexing will lead to fractures and I will end up ripping my bottom bracket out of the frame leading to a catastrophic crash. I don't really fancy bursting a testicle on my top tube as my bottom bracket gives way :shock:

    Maybe you're making more of this than it is. I can't think of an instance where I have seen or even heard of someone "ripping the bottom bracket out...." of a bike. Even a cheap one.
    Maybe some ultra light track bike with some guy on it with "Arnold" legs, maybe. I think you're worried about nothing. In any case if you do" bust a nut" it will probably have to be removed and then you'll win the TDF. Best of both worlds.

    Dennis Noward
  • alfabluealfablue Posts: 8,497
    My steel Dawes Audax flexes a lot around the BB if I really go for it, but its not a problem, its a very comfy and compliant frame, but that is the trade off with slender steel tubes; my Ti MTB (converted for touring) doesn't, neither does my Planet-X carbon as far as I can tell. I don't think it is anything sinister and would not expect any harm to occur - the BB area has got to be the strongest part of the bike, I reckon.
  • dennisndennisn Posts: 10,601
    Wasn't there a post a while back in which someone attempted to disprove the "conventional wisdom" that stiff frames are "better" than flexi ones.
    He tried to "prove" than flexi frames were more efficient than stiff ones.
    I would hazard a guess and say that it probably hasn't been proven either way.
    So the OP's frame may or may not be "the way to go". I await further testing.
    And while I'm at "Why does it seem that no one is able to prove anything about cycling(i.e.
    tubular vs clincher, high cadence vs low, Campy vs Shimano, aero rim vs low profile) that kind of stuff?"

    Dennis Noward
  • alfabluealfablue Posts: 8,497
    I think the only "proofs" lie in mathematics, for everything else there are just degrees of confidence or certainty, which can often come tumbling down.
  • dennisn wrote:
    fuzzynavel wrote:
    Thanks for all your help. I guess I am just worried that I will be powering up a hill and the flexing will lead to fractures and I will end up ripping my bottom bracket out of the frame leading to a catastrophic crash. I don't really fancy bursting a testicle on my top tube as my bottom bracket gives way :shock:

    Maybe you're making more of this than it is. I can't think of an instance where I have seen or even heard of someone "ripping the bottom bracket out...." of a bike. Even a cheap one.
    Maybe some ultra light track bike with some guy on it with "Arnold" legs, maybe. I think you're worried about nothing. In any case if you do" bust a nut" it will probably have to be removed and then you'll win the TDF. Best of both worlds.

    Dennis Noward

    Making more of than it is?? :lol: ....lol there is a reason why this is the beginners forum...I'm a beginner so I wasn't sure and asked the question.....A lot of my questions seem stupid to the more experienced members here...
    I am starting to see the same things cropping up in my short few months as a member here so I am not the only mental newbie here..

    I'll keep pushing for that knackered nut so that I can get free entry to the TDF then! :)
    17 Stone down to 12.5 now raring to get back on the bike!
  • fuzzynavelfuzzynavel Posts: 718
    edited November 2008
    duplicate post
    17 Stone down to 12.5 now raring to get back on the bike!
  • fuzzynavelfuzzynavel Posts: 718
    edited November 2008
    duplicate post
    17 Stone down to 12.5 now raring to get back on the bike!
  • dennisndennisn Posts: 10,601
    alfablue wrote:
    I think the only "proofs" lie in mathematics, for everything else there are just degrees of confidence or certainty, which can often come tumbling down.

    Sort of like the old saying "The only sure thing is that there isn't one". Or something like that. Maybe, "There is no such thing as a sure thing". :wink::wink:

    Dennis Noward
  • dennisndennisn Posts: 10,601
    fuzzynavel wrote:
    dennisn wrote:
    fuzzynavel wrote:
    Thanks for all your help. I guess I am just worried that I will be powering up a hill and the flexing will lead to fractures and I will end up ripping my bottom bracket out of the frame leading to a catastrophic crash. I don't really fancy bursting a testicle on my top tube as my bottom bracket gives way :shock:

    Maybe you're making more of this than it is. I can't think of an instance where I have seen or even heard of someone "ripping the bottom bracket out...." of a bike. Even a cheap one.
    Maybe some ultra light track bike with some guy on it with "Arnold" legs, maybe. I think you're worried about nothing. In any case if you do" bust a nut" it will probably have to be removed and then you'll win the TDF. Best of both worlds.

    Dennis Noward

    Making more of than it is?? :lol: ....lol there is a reason why this is the beginners forum...I'm a beginner so I wasn't sure and asked the question.....A lot of my questions seem stupid to the more experienced members here...
    I am starting to see the same things cropping up in my short few months as a member here so I am not the only mental newbie here..

    I'll keep pushing for that knackered nut so that I can get free entry to the TDF then! :)

    I apologize if you took that wrong. Wasn't meant to be that way.

    Dennis Noward
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