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Weird Rear Wheel Bounce

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  • 09-08-2017 3:31pm
    #1
    devnull
    Moderators, Motoring & Transport Moderators Posts: 11,670 Mod ✭✭✭✭


    Has anyone had an issue with a hybrid/city style bike with a weird rear bounce that only happens when pedaling, it is highly annoying even on smooth ground.

    If I get up to a high speed and take my feet off the pedals it is very smooth which makes me think it must be chain related as the faster I pedal the worse it is but the speed the bike is going doesn't appear to have an effect.

    I have took the wheel off and checked it's in true almost perfectly and all other stuff and it looks totally fine apart from a very small dent which I don't think can be causing this bounce, I put a new wheel on it with new tyre and tube and it's only a tiny tiny bit better which suggests to me wheel is not the root cause.

    What should I be looking for to figure out what is causing it? All gear changes feel fine on all 7 speeds, maybe I'm missing something obvious however....


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    #2
    07Lapierre
    Registered Users Posts: 8,248 ✭✭✭07Lapierre


    Deflate the rear tyre, push the valve into the tyre, then reinflate.


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    #3
    Cee-Jay-Cee
    Registered Users Posts: 12,235 ✭✭✭✭Cee-Jay-Cee


    Is there possibly a small kink in the chain which is giving the effect of a bump each time it forces its way passed a certain part of the RD?

    If you turn the bike upside down with the rear wheel attached and spin the wheels using the pedals can you see any hop in the rear wheel? You might also be able to see if the chain is catching slightly anywhere along the chain line.


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    #4
    devnull
    Moderators, Motoring & Transport Moderators Posts: 11,670 Mod ✭✭✭✭devnull


    07Lapierre wrote: »
    Deflate the rear tyre, push the valve into the tyre, then reinflate.

    I would be surprised if that would help - I've tried a new wheel and new tyre and tube and it still happens which points to it being something other than wheel or tyre unless I am missing something?
    Cee-Jay-Cee wrote: »
    Is there possibly a small kink in the chain which is giving the effect of a bump each time it forces its way passed a certain part of the RD?

    If you turn the bike upside down with the rear wheel attached and spin the wheels using the pedals can you see any hop in the rear wheel? You might also be able to see if the chain is catching slightly anywhere along the chain line.

    I will check after work when I am at home, I didn't see anything obvious though since I checked that briefly when I changed the wheel, but I'll have a look in better light later on, I personally think it's chain related as well, just haven't been able to tie down exactly what the issue is.


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    #5
    tomasrojo
    Registered Users Posts: 11,769 ✭✭✭✭tomasrojo


    Check the chainstays for cracks as well. Not very likely at all, and shouldn't cause a bump, but it did happen to me once, and it does cause the bike to behave oddly on every pedal stroke.


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    #6
    com1
    Registered Users Posts: 459 ✭✭com1


    Maybe its you. If the fit is wrong on the bike you might be stretching too much / little in the pedal stroke causing your body to 'bounce' on the saddle. It is very obvious when looking at someone on a full suss bike that is the wrong size for them, The bike bounces along at every turn of the pedals.


    Try raising / lowering the saddle to fit (I believe your leg should be pretty much straight with your heel on the pedal at its lowest point in the stroke)


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    #7
    devnull
    Moderators, Motoring & Transport Moderators Posts: 11,670 Mod ✭✭✭✭devnull


    Cee-Jay-Cee wrote: »
    Is there possibly a small kink in the chain which is giving the effect of a bump each time it forces its way passed a certain part of the RD?

    If you turn the bike upside down with the rear wheel attached and spin the wheels using the pedals can you see any hop in the rear wheel? You might also be able to see if the chain is catching slightly anywhere along the chain line.

    I have done this now and honestly everything looks and sounds pretty smooth and is virtually silent, nothing catching whatsoever no matter what gear I use, so whatever it is, doesn't occur when the bike is upside down against the ground, but then again gravity might play a part here and obviously it can't when the bike is upside down.
    tomasrojo wrote: »
    Check the chainstays for cracks as well. Not very likely at all, and shouldn't cause a bump, but it did happen to me once, and it does cause the bike to behave oddly on every pedal stroke.

    Had a look and can't see any crack whatsoever, I took the chainguard off as well to see if it made any difference in-case it was catching there and nothing at all was the problem since it was no different with or without it, aside from louder noise from the chain when the guard was not there.
    com1 wrote: »
    Maybe its you. If the fit is wrong on the bike you might be stretching too much / little in the pedal stroke causing your body to 'bounce' on the saddle. It is very obvious when looking at someone on a full suss bike that is the wrong size for them, The bike bounces along at every turn of the pedals. Try raising / lowering the saddle to fit (I believe your leg should be pretty much straight with your heel on the pedal at its lowest point in the stroke)

    It's a bike with 28" wheels, I'm 6ft1 and I ordered the 28" size as opposed to 26" wheel size for exactly the reason you said, the weird thing is that I never had this problem before until a week or so ago and it was always right, I also tried adjusting the saddle profile a little bit yesterday to see if I was bouncing in the saddle and that was causing it, but again makes no difference.


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    #8
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    Perhaps a stupid question ...but are you sure your rear axle is properly seated and fully tightened down?

    (If not ...the torque during pedaling might cause a wobble whereas no pedaling will give a smooth run)


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    #9
    devnull
    Moderators, Motoring & Transport Moderators Posts: 11,670 Mod ✭✭✭✭devnull


    peasant wrote: »
    Perhaps a stupid question ...but are you sure your rear axle is properly seated and fully tightened down?

    (If not ...the torque during pedaling might cause a wobble whereas no pedaling will give a smooth run)

    I actually thought about that already, especially, thinking it could be gravity making the wheel bounce around a little bit due to the torque, so much so that I tightened the screws up further with a wrench and hammer to twist it an extra few mm as tight as it could after replacing the wheel, with no improvement!

    Unfortunately this bike doesn't have a quick release.


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    #10
    ximo
    Registered Users Posts: 20 ✭ximo


    It sounds very strange and annoyingly difficult to pinpoint. Here are a couple things I could think off.

    As you tested with a different wheel it's likely the issue will be near the cranks or the stays.
    It'd far, but did you check the headset for play? It could maybe cause a similar feeling.
    What about the BB, any lateral play?
    Same for the pedals, are they well seated in the cranks? Any play in any direction?
    Take a look to the frame in the places in which the wheel is closer to it. Any rubbing? While stopped, you can try to feel how much lateral play the wheel has by leaning the bike and pushing down from the axle.
    Which type of brakes do you have? Maybe the pads are rubbing?

    Is the bouncing following the speed of the bike or the cadence? Put the bike up to a speed you can feel the bouncing and then change gear. Feel whether the frequency of the wobble changes as well.

    Does the torque you put on the pedals influence in the bouncing? I.e. is the issue only noticeable when pushing hard, or is it evident even with light pedalling?

    Good luck!!


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