Wheel balance

term1te
term1te Posts: 1,462
edited June 2011 in Workshop
When I've got the bike up on the work stand, held on the top tube, and spin the wheels (front or back) the bike rocks up and down. I guess this is due to the wheels not being balanced, i.e. the weight not evenly distributed around the rim. They are both true with no lateral movement in the rims. Is this going to be a problem? If it were a car wheel they'd add those little weights to balance it, but I've never heard of this on bike wheels. I have another set of wheels where the rocking is hardly noticable, so I guess these are balanced?

Thanks

Comments

  • P_Tucker
    P_Tucker Posts: 1,878
    Its the valve, and you'll be fine.
  • term1te
    term1te Posts: 1,462
    P_Tucker wrote:
    Its the valve, and you'll be fine.

    Should have said their tubs, and its there with or without the tubs fitted. Its not the computer magnet either. I doubt it makes much of a difference, but why do they balance car wheels, but not bike wheels? I guess its the speed?
  • rake
    rake Posts: 3,204
    its usually the sleeve join of the rim makes it heavier opposite the valve.
  • skinnypunter
    skinnypunter Posts: 144
    Posher wheels seem to be less prone to this. My Bonty SSRs wobble a bit, a mate's Rovals wobble a tiny amount, and leader of the kit packs Dura-Ace hoops which are smoooooooooooooth. Mind you, he tends to use shorter valve stems than me, and I think there's some reasonable weight there.
  • balthazar
    balthazar Posts: 1,565
    Term1te wrote:
    P_Tucker wrote:
    Its the valve, and you'll be fine.

    Should have said their tubs, and its there with or without the tubs fitted. Its not the computer magnet either. I doubt it makes much of a difference, but why do they balance car wheels, but not bike wheels? I guess its the speed?

    The answer is even more straightforward: bike wheels aren't balanced because it isn't necessary. As we all know from personal experience, unbalanced bike wheels present zero problems at high speeds. Unbalanced car wheels cause obvious problems, which presents the need.

    The reason why it isn't necessary, cannot be speed: bicycles have gone over 100mph many times, setting records for this and that. If my car wheels are out of balance I feel it intrusively at 50mph, a speed I reach most cycle rides.

    I'd guess it has more to to with tyre flexibility, and relative masses: bicycle tyres are small, highly pressurised hoses, whereas car tyres are much higher volume constructions at considerably lower pressures. I can imagine that "shimmy" is induced in this highly elastic structure more readily.

    -edited for clarity-