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Racing roadkill
Guru
If you’re hearing ‘spokey dokeys’ and you have no ‘spokey dokeys’ your hanger is likely hitting the spokes. It’s often caused by the spokes ‘bowing’ under load, which happens to a greater degree, as the wheels wear out over time, or a bent hanger. If it’s a bent hanger, the indexing will likely go to pot as well. If it’s just the spokes ‘bowing’ your wheels are starting to get worn. In the interim, you can wind the ‘L’ screw on the rear derailleur clockwise, a fraction, it will move the limit of the mech outwards a bit.
Cycleops
Legendary Member
- Location
- Accra, Ghana
Your hanger shouldn't be anywhere near the spokes .Cage maybe?
dantheman
Veteran
- Location
- Hitchin, Hertfordshire
A small bend or looseness in the hangar can cause the derailleur to catch, more likely than the hanger itself. You should see marks on the spokes either way - adjust the screw maybe as said, make sure all tight and straight and if continues don't ignore it . I did one year and as I went round a roundabout the derailleur caught properly and ripe off snapping the hanger etc. Luckily it didn't cause a fall or crash and I wasneed too far from home.
rogerzilla
Legendary Member
I get this although the rear mech is well clear of the spokes when parked in the largest sprocket. Something is flexing a lot. I effectively have 9 speeds rather than 10 speeds because I can't use the biggest sprocket for climbing - which is its only purpose.
JtB
Prepare a way for the Lord
- Location
- North Hampshire
Guess I must be one of the few who doesn’t remove the “dork” disc just in case.
Tenacious Sloth
Guru
- Location
- Huntingdon, UK
Why don’t you put a some tipex or similar on the inside of the rear mech?
If it doesn’t wear off then it’s not hitting the spokes.
If it doesn’t wear off then it’s not hitting the spokes.
Ajax Bay
Guru
- Location
- East Devon
This is most likely caused by rear mech hanger alignment (as has been suggested above) @screenman where are you. Get it vertical.
Otherwise, assuming the frame is not flexing abnormally, then the adjustment of the RD is too close to the spokes and wheel flexing under heavy climbing load is causing the cage/spoke interaction. To remedy this I suggest two courses of action: check that the spokes are generally at a decent tension - if confident one could just tighten every spoke by half a turn; and secondly, screw the 'H' limit screw in until it stops the chain climbing on to the largest sprocket (small chainring) and then unscrew it till it will change, just.
2) I wonder what load would cause spokes to 'bow under load'? All spokes stay in tension (in any normal spoked wheel), even when 'unloaded' (ie even the spokes at the bottom quadrant of the wheel).
Otherwise, assuming the frame is not flexing abnormally, then the adjustment of the RD is too close to the spokes and wheel flexing under heavy climbing load is causing the cage/spoke interaction. To remedy this I suggest two courses of action: check that the spokes are generally at a decent tension - if confident one could just tighten every spoke by half a turn; and secondly, screw the 'H' limit screw in until it stops the chain climbing on to the largest sprocket (small chainring) and then unscrew it till it will change, just.
1) As has been said: how can the hanger possibly hit the spokes?
2) I wonder what load would cause spokes to 'bow under load'? All spokes stay in tension (in any normal spoked wheel), even when 'unloaded' (ie even the spokes at the bottom quadrant of the wheel).
Yellow Saddle
Guru
- Location
- Loch side.
[QUOTE 5396085, member: 9609"]Well at least that what it sounds like, the truth is I don't know what is causing the noise.
If I am working at full power in first gear on a steep hill, (esp if the road surface is uneven) I will occasionally get pinging noises as if the hanger is catching a spoke.
I can't recreate it in a way that I can watch what is happening, so any thoughts ?
at rest the hanger when in first is 10mm from nearest spoke.
how much do spokes flex when at full power? or for some reason does the hanger get pulled towards wheel when the chain is at full strain ?[/QUOTE]
A spoke catching on the derailer cage has to do with how the wheel is built. It can be built to avoid the probem but not many wheelbuilders are aware of the problem or understand the mechanism that causes it.
Most derailer cages are chamfered on the spoke side to prevent a touch becoming a catch. The latter is thoroughly unpleasant.
If you look at a typical rear wheel and specifically at the spokes on the right side, you'll notice that the spokes are crossed and interlaced. Crossing most people understand but interlacing is where one spoke is woven over the other so that they touch and pull each other out of line from what would have been a straight line from nipple to hub.
Further, there are two modes of operation for spokes on driven (rear) wheels). The one spoke pushes and the other pulls. These are arranged alternatively. You can figure out which is which by looking at the wheel and imagine twisting the hub as by pedaling. You'll notice that the rear facing spokes will increase in tension and the forward facing ones decrease in tension with pedaling forces. The change in tension is slight, only about 5% for an all-out effort.
However, if the spokes were arranged in such a way that the pulling spoke pushes the pushing spoke inwards with a pedaling pulse, then the spokes move away from the derailer. Arrange them the wrong way and the pulling spoke will push the pushing spoke into the derailer. You can figure this out for yourself by looking at the wheel, imagine the twist in the hub, making vroom-vroom noises and visualising the effect. Remember, the spokes don't follow a straight line and the triangle changes when you increase the tension in the one spoke and decrease tension in the other.
This is exacerbated by having too-few spokes in the wheel. Commercial wheel designers overcome the problem in several ways: by using flat spokes, by radial-lacing the right side spokes (in itself a very bad idea because then the other side has to be crossed and the hub beefed up to transmit torque) or pretending it doesn't exist.
You can fix your wheel by re-building it the other way round.
The problem exists on hub-brake front wheels as well. Here, braking hard, and remember you can decelerate quicker than you can accelerate, spokes can be pulled into the brake caliper if there is too little clearance. In this instance, you have to build the front wheel so that the spokes are pulled into the wheel, not towards the caliper. Shimano even includes such advice in the brochure for front, disc-brake hubs. However, Shimano doesn't bother to explain why.
Some derailers are naturally closer to the spokes than others. Campag is angled to be closer than Shimano, for instance. That's just how it is.
Rim weakness has nothing to do with the phenomena. Lack of rim stiffness deforms the perimeter of the rim. Imagine it changing from a circular to daisy-shape. That's because there is a 10% difference in tension between adjacent spokes under load. When the load is relaxed, the spokes return to even tension.
I hope the last para answers your first question. The other question was about the hanger moving. I take it you mean the "cage moving" because the hanger is part of the frame and doesn't move. The cage is the part of the derailer that houses the two pulleys. The cage doesn't move either, it is the spokes that move towards the cage. The hub, hanger and rim all remain stationary relative to the frame.
If I am working at full power in first gear on a steep hill, (esp if the road surface is uneven) I will occasionally get pinging noises as if the hanger is catching a spoke.
I can't recreate it in a way that I can watch what is happening, so any thoughts ?
at rest the hanger when in first is 10mm from nearest spoke.
how much do spokes flex when at full power? or for some reason does the hanger get pulled towards wheel when the chain is at full strain ?[/QUOTE]
A spoke catching on the derailer cage has to do with how the wheel is built. It can be built to avoid the probem but not many wheelbuilders are aware of the problem or understand the mechanism that causes it.
Most derailer cages are chamfered on the spoke side to prevent a touch becoming a catch. The latter is thoroughly unpleasant.
If you look at a typical rear wheel and specifically at the spokes on the right side, you'll notice that the spokes are crossed and interlaced. Crossing most people understand but interlacing is where one spoke is woven over the other so that they touch and pull each other out of line from what would have been a straight line from nipple to hub.
Further, there are two modes of operation for spokes on driven (rear) wheels). The one spoke pushes and the other pulls. These are arranged alternatively. You can figure out which is which by looking at the wheel and imagine twisting the hub as by pedaling. You'll notice that the rear facing spokes will increase in tension and the forward facing ones decrease in tension with pedaling forces. The change in tension is slight, only about 5% for an all-out effort.
However, if the spokes were arranged in such a way that the pulling spoke pushes the pushing spoke inwards with a pedaling pulse, then the spokes move away from the derailer. Arrange them the wrong way and the pulling spoke will push the pushing spoke into the derailer. You can figure this out for yourself by looking at the wheel, imagine the twist in the hub, making vroom-vroom noises and visualising the effect. Remember, the spokes don't follow a straight line and the triangle changes when you increase the tension in the one spoke and decrease tension in the other.
This is exacerbated by having too-few spokes in the wheel. Commercial wheel designers overcome the problem in several ways: by using flat spokes, by radial-lacing the right side spokes (in itself a very bad idea because then the other side has to be crossed and the hub beefed up to transmit torque) or pretending it doesn't exist.
You can fix your wheel by re-building it the other way round.
The problem exists on hub-brake front wheels as well. Here, braking hard, and remember you can decelerate quicker than you can accelerate, spokes can be pulled into the brake caliper if there is too little clearance. In this instance, you have to build the front wheel so that the spokes are pulled into the wheel, not towards the caliper. Shimano even includes such advice in the brochure for front, disc-brake hubs. However, Shimano doesn't bother to explain why.
Some derailers are naturally closer to the spokes than others. Campag is angled to be closer than Shimano, for instance. That's just how it is.
Rim weakness has nothing to do with the phenomena. Lack of rim stiffness deforms the perimeter of the rim. Imagine it changing from a circular to daisy-shape. That's because there is a 10% difference in tension between adjacent spokes under load. When the load is relaxed, the spokes return to even tension.
I hope the last para answers your first question. The other question was about the hanger moving. I take it you mean the "cage moving" because the hanger is part of the frame and doesn't move. The cage is the part of the derailer that houses the two pulleys. The cage doesn't move either, it is the spokes that move towards the cage. The hub, hanger and rim all remain stationary relative to the frame.
