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Disc Flex

nickyburnellnickyburnell Posts: 18
edited September 2020 in Workshop
Real world experiment: Lots and lots of disc rub out of saddle. Shimano RS505 hubs HPlus Son Arch rims. 32/36 spoke. SPA Cycles build. Pulling rim side to side makes disc move. Messed about with dial gauge and confirmed not frame but actual hub movement. Checked cones, perfect adjustment. Bought a used pair of Mavics and voila, no rub no movement. I should add I would be a Shimano over Mavic person usually. My conclusion is cup and cone on discs is allowing some movement or the hubs are made of something very flexy. Time to find some hubs with same measurements as 505's and de-spoke. Comments more than welcome especially Malcolm :)

Posts

  • pilot_petepilot_pete Posts: 2,120
    The hub body can’t be flexing. Think about it - how can a solid piece of aluminium flex enough for a disc rotor to move by about 1mm?

    It can only be movement between axle and bearings/ hub, quick release (I’m assuming QR rather than thru axle?) or frame flex, assuming the disc rotor is torqued up correctly.

    Are you sure the hub is positioned correctly in the dropouts and the QR done up tightly? Some QRs can be problematic and simply don’t apply enough force. I had QR discs and swapped them for DT Swiss RWS thru bolts. Needed different end caps - not sure if they are available for the RS505 hubs, but they are much tighter when done up.

    PP
  • nickyburnellnickyburnell Posts: 18
    edited September 2020
    Yep, 100% tight, even used Dura Ace skewers. I have an automotive background so not overlooking
    anything. Has to be axle moving ie cone against bearing. I actually tried over tightening cones and it still moved. I would say at least twice the force needed by hand at rim to move the discs on the Mavics v the Shimano. Of course I am now the owner of a floppy Macic freehub but that's another story. I can't find it now but there was another post online ages ago where a change of wheels stopped rubbing, would have liked to have found out hub make. I weigh 90kg btw. I do keep having thoughts about wheel tension this morning though. If design of bearing allows easier movement of axle then as disc is free from axle......I have all the kit so may wind them up a bit more and see. Whatever though I would not recommend these hubs.
  • ugo.santaluciaugo.santalucia Posts: 28,047
    cup and cone moving a bit... you can tighten them, but that might result in premature wear...
    left the forum March 2023
  • david37david37 Posts: 1,313
    Disc brakes suck on road bikes. It's the way it is once you remove the marketing twaddle.
  • pilot_petepilot_pete Posts: 2,120
    Really.... ;)
  • wongataawongataa Posts: 1,001
    david37 said:

    Disc brakes suck on road bikes. It's the way it is once you remove the marketing twaddle.

    Mine don't suck on my road bike.
  • nickyburnellnickyburnell Posts: 18
    Just cured it. Spoke tension. Not knowing what spokes were I didn't go into the depths of calculations but compared a few other wheels, albeit with lower spoke count. Mine were 10 lower on the scale of my meter. Pretty easily wound them up 10 which was about 3/4 turn on all over three passes. No more rub. So hubs can and do flex, especially these. Person that built wheels obviously builds for comfort.
  • ugo.santaluciaugo.santalucia Posts: 28,047
    not sure how spoke tension can impact the disc rotor... but if that solves your problem, then Amen
    left the forum March 2023
  • pilot_petepilot_pete Posts: 2,120
    Spoke tension makes no difference to disc rotor ‘play’, which is attached directly to the hub either by centre lock nut or bolts and which is held by the bearings (cup and cone in your example) on the axle which is locked in the dropouts. Wheel flex yes, but not the hub.

    You could remove all the spokes and rim and still put the hub with rotor in the dropouts held by the QR. Only play in the bearings or movement of the axle in the dropouts can be transferred to the hub body and hence the rotor. I fail to see how spoke tension makes any difference.

    PP
  • Munsford0Munsford0 Posts: 606
    As above, I know how spoke tension can affect brake rub on a rim braked wheel, but I'm at a loss to explain how it could influence disc rub unless the hub is made of parmesan.

    But it clearly has done something; anyone care to theorise about the possible mechanism??
  • ugo.santaluciaugo.santalucia Posts: 28,047
    placebo
    left the forum March 2023
  • First.AspectFirst.Aspect Posts: 13,782
    Retentioning the spokes means you took the wheel out and put it back in properly.
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