bike bouncing with 50mm tubs

adamdavi3s
adamdavi3s Posts: 280
edited July 2011 in Workshop
Hi all,

I'm new to tubs an the joy of 50mm wheels so this might be totally normal...

When spinning the wheels up with the bike on the stand (checking gears) there was a massive amount of 'bounce', almost enough to bounce the stand over!

The wheels are true to 1mm and I did only have the tubs partially inflated!

I'm guessing its something due to the huge difference in aerodynamics of the wheel??

Comments

  • desweller
    desweller Posts: 5,175
    That's out of balance. Is the wheel radially true?
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  • thel33ter
    thel33ter Posts: 2,684
    Is the tub glued on straight?
    And now you know, and knowing is half the battle
    05 Spesh Enduro Expert
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  • adamdavi3s
    adamdavi3s Posts: 280
    I shall check both tomorrow!
  • nferrar
    nferrar Posts: 2,511
    Might not be balanced for the valve although most should be, if you have a sensor magnet on the wheel I'd put it opposite the valve
  • adamdavi3s
    adamdavi3s Posts: 280
    I'll whip out the truing stand tomorrow and see what's on!

    I did wonder if it was the valve but thought it was a daft suggestion.:-D
  • term1te
    term1te Posts: 1,462
    I've got the same issue with some Planet X 50 mm carbon tubs. Doesen't seem to make a difference when you're riding, but on the work stand they are well out of balance. Yes the wheels are true radially and laterally and I notice it with or without the tub glued on. I've put it down to the thickness of the carbon not being even around the rim. I've tried moving the magnet to different spokes, but makes little if any difference. But as I said, I don't notice it on the road.
    The Master
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  • Arghyrou
    Arghyrou Posts: 155
    I also have R50's (like above) from Planet x
    At first I had the same problem, I was using tape, I repositioned the tubs on the rim so they were nearly perfect (took a while), then I pumped up the front wheel to about 100psi and the rear to 140psi. I think this really made the difference as the different pressures dissipated the bounce in them. Definitely worth a try.
  • adamdavi3s
    adamdavi3s Posts: 280
    Thanks chaps these are PRO RC50's

    Firstly the wheels appear to be true so it isn't that!

    I've been experimenting with a magnet and a weight and it does seem to reduce the bounce when I put it opposite the valve.
    I've only got the front down here on the stand at the moment so I can't spin it up massively like the rear (Will be trying it later)

    I don't think it will show up out on the road, I'll find out if the road dries up!

    My only worry is that its not good for them... ?

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