Calcuating tension ratio for different spoke lacings
I've got a set of hubs (Suzue Classica) whose rear hub has pretty dramatically different flange-to-center distances between left and right. When I feed the data into Edd, I get a crazy small left/right tension ratio, something like 41%. In contrast, old Campy Nuovo Record low flange hubs yield a 58% ratio.
One way I can try to move the tension more toward 100% is to reduce the number of crosses on the left side, so 3x on the right, 2x or even 1x on the left. I'd like to get a decent estimate of the resulting tension ratio. Is this something which is easily calculated? Edd doesn't support different number of spoke crossings left v right. Are there online spoke calculators which do? Maybe just a simple formula involving spoke lengths? |
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Where did you learn that by changing the number of crosses would change the tension ratio? I never heard of that.
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That's a large part of the reason I'm asking if the tension ratio can be easily calculated or if there is a spoke length calculator which can take different crossings into account. |
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Like bikinchris said, the most meaningful way to change the spoke tension balance for given flange offsets is to change the number of spokes on each side. This doesn't always require a special hub or rim. For example, you can lace a 32 hole rim to a 32 hole rim by using 16 spokes on the right and 8 on the left, in a quasi "G3" lacing pattern. Or you could use a 24 spoke rim with a 32 hole hub if the rim is center drilled. I've done this several times, and it can work quite well when a stiff rim is used. Out of curiosity, what are the flange offsets of the hub in question? |
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That is an unusually large left flange offset. 130mm road hubs more typically have a 33-36mm left flange offset. Those flange offsets make it a good candidate for 2:1 lacing. If you do build it up with traditional 1:1 lacing, I'd suggest using differential spoking - very thin spokes on the left, and thicker spokes on the right.
By the way, the tension balance is going to be the ratio of the Sines of bracing angles of the right and left spokes. Because the angles are small, they the Sines will nearly proportional to the flange offset distances. So a good approximation of the spoke tension ratio will be the ration of the right/left flange offsets. The ratio of 17.5mm right flange offset and 42.5mm left flange offset is 0.412 (41.2%), which is what the Edd calculator reported. |
Assuming Mark McM's numbers are correct, and we're talking a different number of spokes on each hub flange, then there's little to no value in making an effort to equalize left/right spoke tension.
You want more equal tension for longer lasting wheels-get an off-center rear rim. I build with them and I approve this message. |
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Edit: Also, there's no opportunity to move spacers from right to left, as it's a cartridge bearing hub. |
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https://pacenticycledesign.com/cdn/s...g?v=1547211290 The spoke hole offset will decrease the spoke angles on the left and increase the spoke angles on the right, decreasing dish and tension differential. Asymmetric rims are available from Boyd, DT Swiss, Kinlin, Pacenti, and others. Asymmetric rims are most often found in 25mm - 30mm depths, deeper than a shallow box section rim like an Ambrosio Elite 19mm. The shallowest assymetric rim I'm aware of that is close to a traditional box section rim is the Kinlin XR22RT, which is 24mm wide and 22mm deep. |
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