Pulsing Vibration at High Speed

Discussion in '6th Generation 2002-2013' started by A.M, Nov 6, 2016.

  1. A.M

    A.M Moderator Staff Member

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    Coming home tonight, I noticed something strange at speeds 83 mph or higher:

    1-one thousand, off, 1-one thousand, off...

    The interval for pulsing vibration felt in handlebars.

    I thought it might be road surface. But after fiddling around in gears and speed, it was obvious that:

    No matter the gear, if 83 mph or higher, the pulsing viBratton begins.

    Any ideas?
     
  2. 34468 Randy

    34468 Randy Secret Insider

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    First thing that comes to mind is balance or air pressure in tires. Easy to check and eliminate. Take a look to see if you are missing a wheel weight from your rims. I use dyna beads in mine. Has worked before and no ugly weights on my nice, al be it right now very dirty, white wheels.
     
  3. A.M

    A.M Moderator Staff Member

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    That's where my mind went first as well.

    Air pressure in tires was 32/40. So I had aired up north of Fayetteville, AR to 36/42. So I dismissed that thought.

    There are wheel weights on my rims. Ugly bastages for sure...

    Great idea! I didn't think to check and see if one went missing. I will in the morning though.

    Sent from my SM-G930T using Tapatalk
     
  4. 34468 Randy

    34468 Randy Secret Insider

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    Another thing to look for is cupping on your front wheel. I have no idea what causes this. I have posted up here way back when for ideas why it happens and tried some of the recommendations, but absolutely every front tire I have had on this bike (6 or 7 of them) has cupped. But the only time I noticed any shuddering from this is during an aggressive brake application from high speed.
     
  5. Terry Smith

    Terry Smith Member

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    What you describe sounds like a harmonic vibration where two different frequencies overlap and "beat". So like a wheel weight vibration and (and I'm grasping here) chain vibration, that combine at or above a certain speed.
     
  6. fink

    fink Member

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    best to check your tyres cold and every time before you go for a ride.


    If you saying it's on for a sec then off for a sec then it won't be a wheel weight or chain at that timed interval it is miles too long for that speed. Also not likely to be engine or drive as it was still there regardless of gears/ revs.

    If it had throw a weight then the vibes would have been constant as opposed to on off. I would put it down to road surface.
     
  7. Jeff_Barrett

    Jeff_Barrett Member

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    I couldn't remember if you had beads or weights on your tires. Our tires (T30 Evo) don't seem to get along well with beads - especially in the front tire at the speeds you're indicating. Both times I tried beads in my front tire with the T30 Evos I had to remove the beads and manually balance.

    You could be missing a weight if they were manually balanced.

    Another possibility is that it might be time to replace your front wheel bearings, or something is happening in your front brakes. Have you noticed any change in your fuel economy?

    Also as Randy suggests, cupping - though I haven't experienced that with the T30's like I did with the PR2s (the PR2s were horrible for this).

    Chain is possible too, but you'd likely be feeling it more in your foot pegs, the left one in particular. The chain is practically new though, and your sprockets were in good shape when you changed the chain.
     
  8. kennybobby

    kennybobby New Member

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    It was good to test different gears, speeds and rpm to rule out a lot of other possible culprits.

    Another test you could do is to clamp or tape some weights to the handlebars--try to add at least 1 lb using whatever is available, ankle or small hand weights, etc. securely attached and ride it again to see if the frequency and periodic nature changes.

    At 83 mph the wheel is turning about 20 times/second, or 20 Hz, which is a low bass frequency that you might feel before you could hear it. The tires have about 50 sipes, or channels, per side for shedding water, so that generates a frequency of about 1000 Hz, which is easily heard and felt like 2 octaves above middle C on piano or EVH shredding guitar below the 12th fret on the first string.
    bridgestone_t30_evo_tires_detail.jpg

    You can listen to see what you can hear:
    20 Hz to 20 kHz

    Those sipes could be exciting a resonance of some mechanical thing on the forks or handlebars, which is why adding weight could damp out the vibe and change the effect.

    The sipes are not symmetrical, so they could be generating 2 different frequencies somewhat close together, the result is a beat frequency similar to what you described.

    beats.jpg
     
  9. A.M

    A.M Moderator Staff Member

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    kennybobby, how in the world are people like you so knowledgeable? This is very interesting indeed. Science yo!

    Thank you for sharing. I'm definitely testing next chance I get. This makes complete sense.
     
  10. fink

    fink Member

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  11. James Bond

    James Bond Member

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    Always make sure your tire pressure is 36/42. If you ever get a scalloped wear pattern on your front tire, it's with you until you replace the tire. Ask me how I know. I found out my tire gauge (many years ago) read 4# low cause front (and rear) tire scalloping and eventually a crappy ride. Got a quality gauge and no problems since.

    Check your tire balance too. A tire out of balance doesn't show it at all speeds in my experience. Good luck!
     
  12. Diving Pete

    Diving Pete Member

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    i've not used the standard tyre pressure for years - just cant see it being that.

    Go to a tyre place, get them to remove & refit the tyres - they may have shifted on the bead & are now subtlely out of balance.
     
  13. RobVG

    RobVG Member

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    Put it on the centerstand. Have someone hold the bars tightly.
    Grab the front tire with your hands 180 apart and push and pull back and forth.
    Make sure there is no play.

    Get the front wheel off the ground and give it a spin.
    Look for anything odd.
     
  14. Terry Smith

    Terry Smith Member

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    Good suggestion Rob.

    Just be aware that a failing wheel bearing takes a bit of feeling for. I couldn't feel a problem with my hands at 180 degrees, but getting between the fork leg and the rim I was able to feel a bit of play, sure enough one bearing was on its way out.
     
  15. goinphaster

    goinphaster New Member

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    My bet is on the chain. I have over 50K on the clock and I changed the chain and it got reeeeeeaaaaalllllyyyyy smooooooooooth.
     
  16. DanBjR

    DanBjR New Member

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    Sorry to dig this up but was a solution found?
     
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