Hanger Catching Spokes

[Tenacious Sloth]

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.

Welcome back.

 

[midlife]

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.

Yup, welcome back too sounds to me like the OP has something out of alignment

 

[Salty seadog]

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.

hello you.

please stay around, I've learnt lots from you.

 

[Red17]

Had a similar thing about a year ago, only on steep hills in lowest gear. I originally blamed the wheel but actual cause was a slightly bent hanger.

 

[DCBassman]

Just had exactly this. Very slightly bent hanger just lets the cage touch. Using a long Allen key of the right size, insert into the derailleur fixing bolt on the lower end of the hanger and apply some outward pressure briefly. Do not use a lot of pull.
Should sort it easily. Then check indexing. Then source new hanger anyway, as you don't know what happened to bend it, and it may be failure prone. I'm being VERY cautious here, but...

 

[screenman]

For the few minutes it takes I a baffled as to why people do not check for correct alignment as part of their regular servicing.

 

[Ajax Bay]

Welcome back. On the West Highlands 1000, on the way north from Campbeltown to Oban, I stopped at a hostelry local (as was) to you and described you / your particular strengths/knowledge. "Oh yes" they said "but he's moved - missing him already." I hope 'Loch side' suits (went through there as well, but before dawn).

 

[Yellow Saddle]

For the few minutes it takes I a baffled as to why people do not check for correct alignment as part of their regular servicing.

Because a bent derailer hanger has very specific symptoms which, when absent, doesn't necessitate checking the hanger.

A bent derailer hanger always affect gear changes in an apparently erratic way. Even just a slight bend cause the gears to change fine in one direction but hesitate in the other.

The OP made no mention of any gear change issues at all. For a hanger to bent enough so that the derailer cage hits the spokes, only the completely mechanically unsympathetic cyclist would not have complained about poor shifting.

 

[screenman]

There are I guess plenty that fit that last bit. I think my post was just a thought in the empty space between my ears rather than a reply to the op.

 

[DCBassman]

I've had just this problem. Very slight bend, intermittent pinging, nary a smidgin of poor shifting. This was why I wasn't originally suspecting the hanger, the shifting was fine.

 

[Levo-Lon]

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.

Nice to see you posting @Yellow Saddle

 

[rogerzilla]

I think a lot of modern wheels and frames are just too flexible; only people of a certain weight and leg power who try to pedal them up steep hills ever find out. Mind you, my 1951 Holdsworth had such a flexible fork that it was impossible to ride out of the saddle without really severe, draggy brake rub. I replaced it wirh a heavier fork and all was fine again.

 

[Yellow Saddle]

[QUOTE 5448663, member: 9609"]For some reason it has been fine this last month, but tonight it (the cage thing with the jockeys in) has started to occasionally touch the spokes when under full power.

The cage thing no longer hangs plumb p and down, it has about the same angle as the spokes, top of the cage is about 10mm off the spoke and the bottom jockeys is about 10mm off too.

It also seems quite loose (a lot of sideways play) I guess its just worn. Is it savable, or do I just need a new one. Any suggestions on what I need to buy ?

I don't know how to rotate the video and that music was on the radio - not my choice

View: https://www.youtube.com/watch?v=MU3jQwnlKgQ[/QUOTE]

I still don't suspect the jockey. Remember, tension in the chain only runs along the top of the chain. The bottom doesn't know whether you are putting force on the pedals or not. But now that you've shown a picture of the wheel, I can see it was laced the wrong way around. The spokes on the left move to the centre of the wheel under torque, whilst those on the right move to the right. Maybe another jockey will put a plaster on the problem but the cure is with correct lacing.

 

[Yellow Saddle]

Yup.

 

[fossyant]

[QUOTE 5448663, member: 9609"]For some reason it has been fine this last month, but tonight it (the cage thing with the jockeys in) has started to occasionally touch the spokes when under full power.

The cage thing no longer hangs plumb p and down, it has about the same angle as the spokes, top of the cage is about 10mm off the spoke and the bottom jockeys is about 10mm off too.

It also seems quite loose (a lot of sideways play) I guess its just worn. Is it savable, or do I just need a new one. Any suggestions on what I need to buy ?

I don't know how to rotate the video and that music was on the radio - not my choice

View: https://www.youtube.com/watch?v=MU3jQwnlKgQ[/QUOTE]

Your rear mech is knackered - way too much movement where the cage attaches - you can see it move between the cage and body - it shouldn't. If lucky, you may be able to tighten the bolt that holds the cage on, if not, it's worn out. New one needed.