Wheel deformation under braking

Discussion in 'Bicycle Mechanics and Repairs' started by Armegatron, 7 Apr 2010.

  1. Armegatron

    Armegatron Active Member

    I have noticed that when front braking with my front sus, disc brake bike - the wheel "leans" left in the forks. I have inspected the forks and cant seem to find anything in there that could be the cause, I have also checked the QR tightness and that seems to be ok.

    Im thinking it could be the wheel spoke tension but Im not sure - when viewed from above at rest the spokes on the disc side are protruding from the rim at a shallower angle than the other side (really sorry if this isnt clear).

    Any ideas?

  2. PpPete

    PpPete Guru

    Chandler's Ford
    This is wheel "dish". Much more pronounced on rear wheel with the width of the cassette. In short whatever gubbins hangs on the side of the hub: cassette, disc or whatever, the rim should still be central in the frame.

    Depending on the way it is laced a rear wheel's leading spokes can push against the trailing spokes under heavy load....I've only been aware of this because of potential for spokes to foul the rear mech, but I suppose it would also change the dishing very slightly.... and the reverse effect under heavy braking on a front disc wheel.

    However, it it's as noticeable as you say, I would certainly wonder about spoke tensions. Go round the wheel, one side at a time, plucking the spokes like a guitar string. You should be getting a fairly high clear note, which is more or less the same for all spokes on each side. Disc side should be a slightly higher note.
  3. OP

    Armegatron Active Member

    Thanks Pete,
    Ill have a try plucking them tonight :biggrin: I forgot to mention that when viewed from above and not braking the wheel still sits just slightly to the left of central to the frame. Perhaps the pulling to the left has affected spoke tension and consequently the resting position of the wheel over time.

    Getting a bit disheartened with her at the moment, as the forks are looking a bit rusted (bubbling under the paint) and the bike is barely a year old. :sad: I think (hope) its just cosmetic rust but its not pleasant having a misbehaving wheel and worrying forks :smile:
  4. Globalti

    Globalti Legendary Member

    Have you ridden the bike in salty conditions? The salt will get under the finish on the forks and spread in little fingers.
  5. OP

    Armegatron Active Member

    Rode it all through winter on gritted roads, but washed it after every ride. However, I didnt take the forks apart and wash them out - I just cleaned and lubed up the dust seals at the top each time. What you describe sounds like whats happening though, as the paint is flaky around the bubbles of rust. The colour of the stuff that I got out of the fork when I dismantled it wasnt a rusty reddish colour, it was more of a fine white powder so I suspect that it could have been salt perhaps.

    I cleaned it out with a wire brush and compressed air before lubing up with teflon grease and reassembling and they seem to be smoother in operation. The bits that came out when cleaned were fine and white so I reckon the rusting hasnt compromised strength.
  6. Globalti

    Globalti Legendary Member

    The fine white powder could have been aluminium oxide. Gulp!
  7. 02GF74

    02GF74 Über Member

    Are you saying that you can see the wheel lean over when you apply the front brake?:smile:

    You do not say what bike and or wheel it is.

    I am guessing, and may be far off the mark, but you have a £ 200 full suspension bike so to sell for that price, it was to have parts made from cheese and other cheap componentry - sorry. :biggrin:

    Otherwise there is something wrong, certainly should not do that.
  8. OP

    Armegatron Active Member

    Bike is Scott Sportster P55:

    Wheel is Zac19 or something.

    I think the problem is linked to the forks, and I suspect that when I receive the new parts for the fork (a plastic sleeve on each stanchion that takes up the slack and play in the suspension) the problem should resolve itself, as it appears that is where the play is at as opposed to the wheel being an issue. The new sleeves should have a tighter fit and take up any slack between the two sides.

    I twanged the spokes as suggested and there were no dull tones, everything seemed "bright".

    I also took another look inside the fork housing and the white powdery stuff has gone leaving behind a smooth looking surface where I had cleaned it off - so perhaps it was dried grease (the forks insides were quite dry when I disassembled them) or something other than metal / rust?

    Ill try and get some photos tonight of everything to explain what Im seeing.

    Globalti: could this be Aluminium Oxide? I think the forks are steel. Whats the implications if it is alu oxide - structural failure?
  9. 02GF74

    02GF74 Über Member

    Well, I have to eat my words. A google for you bike shows it as: £999,999.00

    that is more than I paid for my house, bikes, cars and everything else I own., maybe by a factor of 2 or 3 !!!!

    .... but serioulsy, probably a £ 300 ish bike so the wheel should not be an issue.

    have to admit I am not really getting what you are saying with the wheel moving, spacers, and forks issue. in your price brakcet, the forks should be good'uns too.
  10. OP

    Armegatron Active Member

    :biggrin: I think I defiantly got a bargain of the century there then :biggrin: I paid £450 if I recall correctly. The new parts have arrived for the forks so I will be fitting them tonight to see if there is any improvement, but Ill also take some pictures to hopefully illustrate what is happening and what I believe is the cause.

    A quick look for my forks online reveals that CRC sells the 63mm (not the 50mm thats on mine) V-brake version for £39.99. Not sure if that's cheap or expensive to be honest. If it does turn out to be emanating from the forks and its beyond repair Ill either upgrade slightly (mechanical lockout) or buy something similar to the ones that are on it.

  11. 02GF74

    02GF74 Über Member

    RRP £ 50; even so, that is dead cheap for suspension forks.

    V-brake is no good for you since you have disc brake - but in theory apart from the sliders, the other bits may be compatible.

    For what I would call as decent forks, I'd say you'd need to spend circa £ 200.
  12. OP

    Armegatron Active Member

    I dont really do a huge amount of rough stuff, downhills or anything like that. I wanted some degree of front suspension to take some of the shock from smaller bumps as I found it helped my back (slipped disk). So super duper forks arent probably necessary for me, so perhaps £50ish for forks is a sensible price for my use.

    Cheers for the advice and help though - the parts that Im talking about are 2c on this exploded diagram:

    When I reassemble tonight, am I ok to use copious amounts of this Teflon grease:
  13. OP

    Armegatron Active Member

    Received parts but unfortunatly the part number on the sleeve is FEE460 - the part number sent was FEE460 yet the replacement is too big. Hopefully I will eventually get the right part but if not Ill need to start looking to buy some replacement forks.

    Pictures hopefully attached:
    The left plastic sleeve is in place, the right one is removed.

    The plastic sleeve takes up the slack between the "rods" and the housing.

    The inside of the fork housing now looks fairly clean.
  14. Tis a cheap fork with little structural rigidity. Applying the (disc) brake loads one fork leg which twists accordingly. The only components acting against this twisting are the built in fork brace (the arch which connects the two sliders) and the interface of the axle and skewer in the drop out. Upgrading the brace is impossible as it is a built-in part of the casting. Upgrading to a larger axle and the added tortional stiffness this would bring would require a new wheel. 'Spensive. The two remaining options are; Upgrade to a more robust skewer (Olde fashioned Shi**no steel ones are the best) or replace the fork.

    I suggest; if you stop looking at the front wheel when you are braking, the whole thing will cease being a problem.

    Fork manufacturers have been working on this issue for ever, the original 'upside down' fork equipped Mountain Cycle would veer violently to the right when you applied the brake.
  15. OP

    Armegatron Active Member

    Thanks. Im having trouble sourcing parts for the fork at the moment so it may come down to finding a replacement anyway - however with a tight budget I wont be looking at upgrading and may just go for something else in the £50-£80 range.

    I just found it strange that in the time Ive been riding it I have only recently noticed this, so while not looking at it while braking seems the cheaper option I would be concerned incase it got worse and be looking at it even more:sad:

    I have to say that so far Greyville who distribute Suntour forks in the UK have been very helpful and fingers crossed with their help Ill be able to find the parts to make the bike rideable soon before I go out of my mind.
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