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What was actually carried by Jim Blackburn front racks?

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What was actually carried by Jim Blackburn front racks?

Old 12-28-20, 06:57 PM
  #51  
Duragrouch
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Regarding front racks:

Low riders are preferred, not just for lower center of gravity, but because it centers the load on the steering axis, so less rotational inertia. Having said that, it's harder to use low riders on a 20" wheel folder. Those small front racks just big enough for a trunk bag or six-pack of something (hence the rack name of "sixer"), while being small on a full size bike, are perfect size on a 20" wheel, and the ones that attach to the brake bosses are interchangeable, as the different distance to the axle center matters not. However, hanging panniers from it, with no struts to the ends of the fork, the panniers can hit the spokes, so on mine, I'll be adding something like that. But at $10 new price, the rack is a real bargain.

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Old 01-01-21, 08:00 AM
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Originally Posted by Duragrouch View Post
Unrelated, but is that front radial spoking on a vintage hub?
Sure. Lots of people used to do it. It actually wasn’t that vintage when it was built
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Old 01-01-21, 02:00 PM
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Originally Posted by Bianchigirll View Post
Sure. Lots of people used to do it. It actually wasn’t that vintage when it was built
The only reason I'm speaking is a potential safety issue, not style. Radial spoking should only be done on hubs designed for it. If not designed for that load direction, the hub will develop fatigue cracks between spoke holes (not immediate, but over time), and since that stress is equal all the way around the hub flanges, you could have a catastrophic failure where the crack "unzips" and propagates all the way around, causing loss of control of the bike. Hopefully, a failure at just one or two spoke holes will lesson tension enough on the other spokes to stop the propagation. More spokes helps to reduce stress, but also places the hub flange spoke holes closer together, increasing the stress between holes and likelihood of failure. Conversely, tangential spoking puts lower stress on the hub for the same tension because there is more metal to support the load in that direction. Older hubs were not designed for radial spoking, I've seen this failure before when radial spoking first became trendy but hubs hadn't caught up. If your hubs are not as vintage as the bike and are designed for radial spoking, no worries.
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Old 01-01-21, 03:15 PM
  #54  
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Originally Posted by Duragrouch View Post
The only reason I'm speaking is a potential safety issue, not style. Radial spoking should only be done on hubs designed for it. If not designed for that load direction, the hub will develop fatigue cracks between spoke holes (not immediate, but over time), and since that stress is equal all the way around the hub flanges, you could have a catastrophic failure where the crack "unzips" and propagates all the way around, causing loss of control of the bike. Hopefully, a failure at just one or two spoke holes will lesson tension enough on the other spokes to stop the propagation. More spokes helps to reduce stress, but also places the hub flange spoke holes closer together, increasing the stress between holes and likelihood of failure. Conversely, tangential spoking puts lower stress on the hub for the same tension because there is more metal to support the load in that direction. Older hubs were not designed for radial spoking, I've seen this failure before when radial spoking first became trendy but hubs hadn't caught up. If your hubs are not as vintage as the bike and are designed for radial spoking, no worries.
I am not sure I’ve ever heard of hub “unzipping” but I have seem the results of a flange break at a spoke hole. As strange as this sounds the rider didn’t suddenly and catastrophically tumble to ground suffering disfiguring injuries. He did have a nice slow wobbly ride home though.
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Old 01-01-21, 04:49 PM
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Originally Posted by Bianchigirll View Post
I am not sure I’ve ever heard of hub “unzipping” but I have seem the results of a flange break at a spoke hole. As strange as this sounds the rider didn’t suddenly and catastrophically tumble to ground suffering disfiguring injuries. He did have a nice slow wobbly ride home though.
There are two kinds of flange breaks possible, one where there is a separation of material from a single spoke hole, and the other, a crack from one spoke hole to another. I have experienced the latter, not with regard to radial spoking, but long before I became an engineer and understood the issues. I was in my youth and relatively poor and salvaged a wide-flange hub from a crash by straightening the bent flange, especially bad with aluminum as it has poor fatigue strength versus steel. Fortunately, like you said, the failure of spoke tension on two adjacent spokes immediately lowered spoke tension on the whole wheel, and thus did not unzip beyond those two spoke holes. But even that, you don't want, because then your hub becomes a paperweight, no? But I have also seen more severe failures on radial spoked wheels of others' bikes, when the failure happened under higher loading. This is more likely to happen with a high spoke number (like 36 hole) on a small flange aluminum hub (because the spoke holes are closer together) that is not designed for radial spoking.

I'm not against others using radial spoking on a non-driven wheel or non-drive side on a rear hub, especially when designed for it. But I, myself, avoid radial spoking (and low spoke count) like the plague for my own bikes, for higher hub stress, shorter spokes so rides worse, no spoke lacing to help maintain tension, etc. I don't need the reduced weight and supposed aero drag reduction of radial. But again, unless it's a safety issue, I say nothing. My only concern in your case was, given the wide flange hub, I thought it might be older, and thus possibly not designed for radial lacing.

I don't mean to step on you at all, just trying to share some things I have learned, especially with regards to safety, I worked in safety critical industries. My education and career as a mechanical engineer on wheeled vehicles helped me understand all things bicycle a lot better, especially part failures and vehicle dynamics.
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Old 01-01-21, 07:42 PM
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Originally Posted by Duragrouch View Post
There are two kinds of flange breaks possible, one where there is a separation of material from a single spoke hole, and the other, a crack from one spoke hole to another. I have experienced the latter, not with regard to radial spoking, but long before I became an engineer and understood the issues. I was in my youth and relatively poor and salvaged a wide-flange hub from a crash by straightening the bent flange, especially bad with aluminum as it has poor fatigue strength versus steel. Fortunately, like you said, the failure of spoke tension on two adjacent spokes immediately lowered spoke tension on the whole wheel, and thus did not unzip beyond those two spoke holes. But even that, you don't want, because then your hub becomes a paperweight, no? But I have also seen more severe failures on radial spoked wheels of others' bikes, when the failure happened under higher loading. This is more likely to happen with a high spoke number (like 36 hole) on a small flange aluminum hub (because the spoke holes are closer together) that is not designed for radial spoking.

I'm not against others using radial spoking on a non-driven wheel or non-drive side on a rear hub, especially when designed for it. But I, myself, avoid radial spoking (and low spoke count) like the plague for my own bikes, for higher hub stress, shorter spokes so rides worse, no spoke lacing to help maintain tension, etc. I don't need the reduced weight and supposed aero drag reduction of radial. But again, unless it's a safety issue, I say nothing. My only concern in your case was, given the wide flange hub, I thought it might be older, and thus possibly not designed for radial lacing.

I don't mean to step on you at all, just trying to share some things I have learned, especially with regards to safety, I worked in safety critical industries. My education and career as a mechanical engineer on wheeled vehicles helped me understand all things bicycle a lot better, especially part failures and vehicle dynamics.
I’ll just toss all my wheels in the trash since they are old and I have no way of knowing if the hubs were ever radially laced before I got them.
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Old 01-01-21, 09:58 PM
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Originally Posted by Bianchigirll View Post
I’ll just toss all my wheels in the trash since they are old and I have no way of knowing if the hubs were ever radially laced before I got them.
I suspect you are being facetious, but in case not, I think that might not be necessary. Periodic inspection for cracks is good. While ferrous metals can be inspected with a magnetic process like Magnaflux, a non-magnetic material like aluminum can be inspected with a simple "dye penetrant", basically any dye, even a sharpie marker and little solvent like alcohol, but they make dedicated spray liquids for this; The dye will accumulate in even tiny cracks, making them more visible.

Cross-laced spokes also leave "witness marks" in the direction of the spokes on the outside of the flanges where the spokes bend inward and contact the flange. This is not evident on radial lacing where the spoke head is on the outside of the flange and the spoke extends radially from the inside of the flange. However, you might be able to see a witness mark indicating spoke direction due to the bend radius at the spoke head, leaving a corresponding mark at each spoke hole on the inside of the flange. But again, even if used radially, with periodic inspecting for cracks, you may be fine. Fatigue cracks take a while to start and then propagate over time. Even if I'm using a hub in the matter intended (as well as other parts such as the bike frame), I've learned to periodically inspect, I've had cracks pop out of nowhere even under gentle use.
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