Possible damge?

Discussion in 'General Bike Discussion' started by IanHighfield, Dec 16, 2009.

  1. IanHighfield

    IanHighfield New Member

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    I only use rollers for indoor riding. Resistance trainers that clamp to the rear axle and hold the bike on the roller are very popular.

    Looking at these devices and watching riders while using them, I come away thinking they cannot be good for the rear triangle. I see a good bit of twist and torque racking the rear as the bike is pedaled hard. On an unbridled bike, this is not as present because the bike frame (as a unit) can move a little bit. Not so on the axle-clamped resistance machine. All the stress goes into bending rear triangle members.

    I've never heard of this being a problem. It just looks tough on the bike to my eyes. Anyone have thoughts, or long-term experience with this kind of training device?
     
  2. whyeyebike

    whyeyebike New Member

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    I am curious about this topic as well so thanks for starting the thread. This is my first real off season using a trainer and the other night I was looking down at my rear wheel while chugging along thinking, "this can't be good for my bike". I guess my deepest fear is that I do some type of serious damage to my bike while on the trainer. I only have 1 road bike and no money to get another.
     

  3. Industry_Hack

    Industry_Hack Total noob (& forum admin) Admin Staff Tavern Member

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    That would suck to break your bike in your living room.
     
  4. IanHighfield

    IanHighfield New Member

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    whyeyebike: Hope I haven't scared you off the trainer. I tend to think if these things ruined frames we would have heard about it a long time ago via the internet. I think bike makers would be screaming too. I don't hear such things.

    I was just curious to see if others (and you do) see the same kind of twisting going on behind. I've sat a few of these trainers and think a person should get on and off carefully inline with the bike. Don't hang off the side with the rear axle locked and unable to rotate toward the force. Use a step, a thick book or something, and get your body weight centred and on the seat before clipping in. Anything to keep from tipping left or right. When pedaling maybe staying away from humping gears and sticking to spinning would be better too. Nobody gets better in the winter. You simply want to stay somewhat even and ready for spring. Keeping your bum in condition is always a plus too, low-level winter spinning will do this.
     
  5. whyeyebike

    whyeyebike New Member

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    Its right up there with my fear of coming off rollers and crashing into my plasma tv in the middle of a work out. That would only be cool if a video camera is running.
     
  6. whyeyebike

    whyeyebike New Member

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    Don't worry, it takes more then that to keep me off the bike....and since the weather isn't the greatest, the trainer is all I got. And I think your right, there would be all kinds of warnings and horror stories being told if bikes were easily damaged on trainers.
     
  7. jeepster93

    jeepster93 New Member

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    WOW...
    You guys are amazing...

    I just came her to ask if my fancy, sort of new, road bike, will get hurt being used on a trainer.

    It has a carbon fiber fork and rear triangle on an aluminum frame.

    I only have a stationary trainer.

    Only guessing...
    It should flex enough for this...


    Oh man...
    I HOPE SO!!!
     
  8. Industry_Hack

    Industry_Hack Total noob (& forum admin) Admin Staff Tavern Member

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    Carbon fiber and aluminum aren't really known for their elasticity.
     
  9. retromike3

    retromike3 retromike3

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    rigid frame is a misnomer

    I think the reason you are noticing the flex in your frames is that's all your looking at. Carbon fiber does flex quite a bit or your bike would hurt like hell to ride. the main problem with carbon frames when they first came out was that after a good hard season of riding they would delaminate. The problem was that after thousands of flexes the glue that held the layers together would brake and the tubes would get progressively more flexible. At a friends shop in Portland we had a guy who had a special Trek time trial bike made for the Tour. It was a design that was outlawed by the tour officials so he got it for a song. After about a year of triathlons the bottom bracket was quite "Limp" There was nothing we could do and it was not under warranty so I guess he has got a whole bunch of top line Durace parts and a neat looking sculpture to hang on the wall.

    There is a comparatively lot of movement in a bike frame under the loads when you ride your bike. and even with the wimpy 1/4 horsepower that the average club rider put out it will make a big impact on your bike when you are peddling it down the road or across the finish line.

    The reason steel frames are still being made today is the fact that they seem to have a almost unlimited ability flex and come back to the original shape millions of times without losing the "spring" or at least most of the spring that they came with. I don't know if they still publish the magazine Bike Science when they went all over those topics with F.E.A. (Finite Element Analyses) and It showed some interesting things.

    And the reason you don't notice all of this happing wile you "on the road" is that you are paying attention to that S.U.V. coming at you with the driver yelling into his headset instead of the 3 millimeter flex at your chain stay.

    JUst a thought Mike Frye the bike guy
     
  10. Industry_Hack

    Industry_Hack Total noob (& forum admin) Admin Staff Tavern Member

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    Please define "Flex".

    A bicycle frame should only ever "give" on one plane.
     
  11. retromike3

    retromike3 retromike3

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    flex or something like that

    B.I.T.D. one of my good friends did some work with F.E.A. on bikes. So I did get some of this information second hand but here is a link to the Sheldon sight that brings up just the data I was talking about.(sorry I could not paste it here my computer does not have a good graphics program so I could insert it here.
    Finite Element Structural Analysis: A New Tool for Bicycle Frame Design, by Leisha A. Peterson and Kelly J. Londry

    note the figure 7 and the relation to pedaling.

    Mike Frye
     
  12. retromike3

    retromike3 retromike3

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    sorry it was figure 6 not seven(its bin a long day.)