Dura-Ace 7900 rear hub numbers
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Dura-Ace 7900 rear hub numbers
Contemplating a build using a 7900 straight-pull 20H hub. I have so far deduced that Shimano made the 7900 rear hub as standard drilled flange and also as a straight-pull 20H on Dura-Ace wheelsets only e.g., C35. The perplexing thing is that I see no part numbers which distinguish the two hubs. There is tech data from Shimano giving the 7900 dimensions but I'm guessing this is for the standard flange model which came as part of a group set. Any insight on this? Does anyone know the hub data for the straight-pull hub?
Addendum: I know it can be measured. The the exact spoke circle would, I think, have to be computed using the polygon formed by the five spoke anchors. This is a polygon inscribed in a circle with the veritices on the circle. We're solving for the circle perimeter only knowing the length of the polygon sides. I can't find or recall the procedure for that. I think this what was called "squaring the circle" (impossible). Any math types feel free to weigh in there.
Addendum: I know it can be measured. The the exact spoke circle would, I think, have to be computed using the polygon formed by the five spoke anchors. This is a polygon inscribed in a circle with the veritices on the circle. We're solving for the circle perimeter only knowing the length of the polygon sides. I can't find or recall the procedure for that. I think this what was called "squaring the circle" (impossible). Any math types feel free to weigh in there.
Last edited by crewdoglm; 12-31-13 at 01:03 PM. Reason: More
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I suspect that all tech info relating to the shell and spoking would be for the standard drilled hubs, since Shimano didn't (doesn't) offer the straight pull version for sale separately. The rest of the data, such as service and internals may be common to both.
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I have a pair of Shimano WH-R560 prebuilt wheel (~105 level) that uses a specific radial laced front hub and a specifically designed rear hub laced radially on the drive side and 2X on the non-drive side and both hubs have the nipples at the hub flanges. I have never seen anything like them sold as individual hubs. Their internals and freehub body are otherwise completely conventional Shimano.
#4
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Measuring j-bend hubs is easy but I have no idea how to measure a straight pull hub.
This is taking the long way around, but you could look at the tech docs and see what spoke length Shimano used. Then figure out the ERD of the rim they used. This might get you in the right direction???
This is taking the long way around, but you could look at the tech docs and see what spoke length Shimano used. Then figure out the ERD of the rim they used. This might get you in the right direction???
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Measuring j-bend hubs is easy but I have no idea how to measure a straight pull hub.
This is taking the long way around, but you could look at the tech docs and see what spoke length Shimano used. Then figure out the ERD of the rim they used. This might get you in the right direction???
This is taking the long way around, but you could look at the tech docs and see what spoke length Shimano used. Then figure out the ERD of the rim they used. This might get you in the right direction???
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However I believe that MrRabbit here on BF has a conversion, or a calculator for these. Otherwise I've always done it with a sketch and a calculation of the straight line distance to which I add 1mm for every 10mm of center-to-flange measurement.
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That is good info. Thanks. If the right center-to-flange is 18, understand you would add 1.8MM to the number given for a J-bend?
As to my initial question, thanks to Dr. Peterson of Drexel University for straightening me out. (This is not a case of "squaring the circle.") Happy to now know: there is a constant relationship of "regular" polygons to a circumscribed circle around said polygon. The constants are set forth in the CRC Standard Mathematical Tables. Measuring one side of our pentagon-shaped hub yields a drive side diameter of 48.14 MM and a left side diameter of 28.3. I would be fascinated to learn how this compares Shimano's unpublished data. The difficulty is in positioning the calipers to measure precisely between the spoke heads.
As to my initial question, thanks to Dr. Peterson of Drexel University for straightening me out. (This is not a case of "squaring the circle.") Happy to now know: there is a constant relationship of "regular" polygons to a circumscribed circle around said polygon. The constants are set forth in the CRC Standard Mathematical Tables. Measuring one side of our pentagon-shaped hub yields a drive side diameter of 48.14 MM and a left side diameter of 28.3. I would be fascinated to learn how this compares Shimano's unpublished data. The difficulty is in positioning the calipers to measure precisely between the spoke heads.
Last edited by crewdoglm; 12-31-13 at 06:07 PM.
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In a perfectly tangent spoke pattern the spoke length would be very close to 1/2 the ERD plus the CTF adjustment.
Looking at your hub, calculate/measure how far from the halfway plane the spokes end at, subtract from half the ERD, add for CTF and you'll be within 1mm. I do this using a careful sketch of the hub profile, then indicate the spoke routing and measure.
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Got it. Your technique obviates the need for a spoke circle diameter number. And that number is often absent with the "star" hub. Still straight pull wheels are being built all the time which invites the question of a standardized technique. I guess I'm thinking there must be a correction for j-bend lengths out there using an effective spoke circle D. DT Swiss publishes this number for their straight pull hub which has a less pronounced star shape.
Last edited by crewdoglm; 12-31-13 at 07:20 PM. Reason: error
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Got it. Your technique obviates the need for a spoke circle diameter number. And that number is often absent with the "star" hub. Still straight pull wheels are being built all the time which invites the question of a standardized technique. I guess I'm thinking there must be a corrected j-bend lengths out there using an effective spoke circle D.
BTW-mas I said earlier, I believe MrRabbit has a spoke calculator that handles star hubs (or a formula for adjusting standard measurements. If he doesn't post here soon, you might PM him.
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Last edited by FBinNY; 12-31-13 at 07:23 PM.
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Roger that. Sounds like you've got some years on me but FWIW I appreciate that perspective truly. I teach math/charts & graphs stuff in aviation and see I excessive reliance on technology. The problem is that bad conceptual knowledge prevents errors from being caught. (The machine isn't wrong but it won't tell you when you're f--ing up either.)
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Roger that. Sounds like you've got some years on me but FWIW I appreciate that perspective truly. I teach math/charts & graphs stuff in aviation and see I excessive reliance on technology. The problem is that bad conceptual knowledge prevents errors from being caught. (The machine isn't wrong but it won't tell you when you're f--ing up either.)
I built wheels for over 20 years and never knew the spoke tension. There were only three tensions following the Goldilocks rule -- too loose, too tight and just right. I still use my judgement, and tactile feedback while building, then use a tension meter only as a sort of reality check. While the tension meter gives me a number, it's not that useful since I don't have a predetermined target number, only a range.
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Impressive. I am happy as hell to get it true and tight any way I can and the tension meter plays heavily into that. LAUGHING AT MYSELF HERE. Those aviation crashes you mention are ultimately driven by the dollar. When every flight must produce revenue, the company wants to minimize the number of human beings in thing receiving a salary. Worse, they're never going to admit that the lack of a real systems expert (flight engineer or the loadmaster) is what killed everybody. The FAA could start requiring it... Happy New Year to you.
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Those aviation crashes you mention are ultimately driven by the dollar. When every flight must produce revenue, the company wants to minimize the number of human beings in thing receiving a salary. Worse, they're never going to admit that the lack of a real systems expert (flight engineer or the loadmaster) is what killed everybody. The FAA could start requiring it... Happy New Year to you.
Do you tie and solder?
Do you tie and solder?
As for airplanes, I don't think an additional crewman would make a difference. The problem is that the avionics are so good, and so reliable that many pilots have zero experience actually in control. So, in those rare instances where the systems fail you have a pilot that despite 10 years flying, and never dealt with a crisis. Moreover that have no feel for the controls and are incapable of seat of the pants flying.
I learned this when I was certified as a scuba diver, where the process involved many hours of classroom work, learning nonsens like decompression theory, and how to plan dives using tables. That was followed by pool and open water work drilling emergency procedures such as such as controlled out of air ascents. At the end of the course the instructor commented that, sadly, all the drills were probably wasted effort since the equipment was so reliability that years might go by before we needed to manage a crisis, and by then we'd have forgotten all the drills.
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True the equipment is very reliable, but failures are essentially random so though years may go by between failures on average, it's possible for only a day to go by before one. You can choose to remain current with emergency procedures either by reviewing and practicing procedures on your own, or by taking recurrency classes. Failures are really rare in commercial passenger airline operations too, but pilots are required to undergo recurrency training twice a year anyway.
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True the equipment is very reliable, but failures are essentially random so though years may go by between failures on average, it's possible for only a day to go by before one. You can choose to remain current with emergency procedures either by reviewing and practicing procedures on your own, or by taking recurrency classes. Failures are really rare in commercial passenger airline operations too, but pilots are required to undergo recurrency training twice a year anyway.
If you look at the diving world, most open water divers are pretty complacent, however cave divers who are very aware of the unforgiving nature of the environment do multiple predive checks, including various emergency drills before every dive.
I'm not anti technology at all, but it's important to recognize that relying on technology means a loss of the day to day experience that creates the instincts we may need in an emergency. Somehow we need to find a way to use modern tools without letting old skills atrophy.
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Working with straight pull hubs and spokes from a calculation standpoint is pretty simple actually:
1. Just like the end points of the spokes define a virtual circle with a virtual diameter we call "ERD"...
2. Straight pull spoke seats define a virtual flange diameter that we typically reference as flange diameter - center-to-center.
With twin-thread setups it's even more fun - because you have to establish the minimum insertion required by the manufacturer - THEN - define the virtual flange diameter. It'll always be smaller then the physical flange - just like with standard hubs.
Calculating the spokes as usual is a piece of cake.
I share the beef of others who wish manufacturers of boutique wheels would publish their hub dimensions with references and their rim dimensions with references - not everyone trusts the repair skills of the LBS that sold 'em the boutique wheel.
=8-)
As an aside, one of my favorites is the bmx hub that looks like a straight pull hub but requires traditional j-bend spokes. I don't remember whether it's Atomlab or someone else...
You stick the j-bend spoke in - and then turn the spoke 90 degrees - just like that you have a straight pull j-bend spoke.
So the "effective flange diameter" - otherwise hereby know as "EFD" (smacks self in face) is roughly 2mm or 3mm below the surface of the the hub shell.
Yeah...I know...
Hippy New Beer!
...and enjoy your knew reference.
=8-)
1. Just like the end points of the spokes define a virtual circle with a virtual diameter we call "ERD"...
2. Straight pull spoke seats define a virtual flange diameter that we typically reference as flange diameter - center-to-center.
With twin-thread setups it's even more fun - because you have to establish the minimum insertion required by the manufacturer - THEN - define the virtual flange diameter. It'll always be smaller then the physical flange - just like with standard hubs.
Calculating the spokes as usual is a piece of cake.
I share the beef of others who wish manufacturers of boutique wheels would publish their hub dimensions with references and their rim dimensions with references - not everyone trusts the repair skills of the LBS that sold 'em the boutique wheel.
=8-)
As an aside, one of my favorites is the bmx hub that looks like a straight pull hub but requires traditional j-bend spokes. I don't remember whether it's Atomlab or someone else...
You stick the j-bend spoke in - and then turn the spoke 90 degrees - just like that you have a straight pull j-bend spoke.
So the "effective flange diameter" - otherwise hereby know as "EFD" (smacks self in face) is roughly 2mm or 3mm below the surface of the the hub shell.
Yeah...I know...
Hippy New Beer!
...and enjoy your knew reference.
=8-)
__________________
5000+ wheels built since 1984...
Disclaimer:
1. I do not claim to be an expert in bicycle mechanics despite my experience.
2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:
Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life
5000+ wheels built since 1984...
Disclaimer:
1. I do not claim to be an expert in bicycle mechanics despite my experience.
2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:
Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life
#18
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Working with straight pull hubs and spokes from a calculation standpoint is pretty simple actually:
1. Just like the end points of the spokes define a virtual circle with a virtual diameter we call "ERD"...
2. Straight pull spoke seats define a virtual flange diameter that we typically reference as flange diameter - center-to-center.
With twin-thread setups it's even more fun - because you have to establish the minimum insertion required by the manufacturer - THEN - define the virtual flange diameter. It'll always be smaller then the physical flange - just like with standard hubs.
Calculating the spokes as usual is a piece of cake.
I share the beef of others who wish manufacturers of boutique wheels would publish their hub dimensions with references and their rim dimensions with references - not everyone trusts the repair skills of the LBS that sold 'em the boutique wheel.
=8-)
As an aside, one of my favorites is the bmx hub that looks like a straight pull hub but requires traditional j-bend spokes. I don't remember whether it's Atomlab or someone else...
You stick the j-bend spoke in - and then turn the spoke 90 degrees - just like that you have a straight pull j-bend spoke.
So the "effective flange diameter" - otherwise hereby know as "EFD" (smacks self in face) is roughly 2mm or 3mm below the surface of the the hub shell.
Yeah...I know...
Hippy New Beer!
...and enjoy your knew reference.
=8-)
1. Just like the end points of the spokes define a virtual circle with a virtual diameter we call "ERD"...
2. Straight pull spoke seats define a virtual flange diameter that we typically reference as flange diameter - center-to-center.
With twin-thread setups it's even more fun - because you have to establish the minimum insertion required by the manufacturer - THEN - define the virtual flange diameter. It'll always be smaller then the physical flange - just like with standard hubs.
Calculating the spokes as usual is a piece of cake.
I share the beef of others who wish manufacturers of boutique wheels would publish their hub dimensions with references and their rim dimensions with references - not everyone trusts the repair skills of the LBS that sold 'em the boutique wheel.
=8-)
As an aside, one of my favorites is the bmx hub that looks like a straight pull hub but requires traditional j-bend spokes. I don't remember whether it's Atomlab or someone else...
You stick the j-bend spoke in - and then turn the spoke 90 degrees - just like that you have a straight pull j-bend spoke.
So the "effective flange diameter" - otherwise hereby know as "EFD" (smacks self in face) is roughly 2mm or 3mm below the surface of the the hub shell.
Yeah...I know...
Hippy New Beer!
...and enjoy your knew reference.
=8-)
So when you do a length computation on a funky straight-pull hub, having found the EFFECTIVE flange diameter, is there any OTHER correction made to the length indicated for a J-bend spoke? Guessing not Thanks!