Calcuating tension ratio for different spoke lacings

[smontanaro]

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?

[RobJ]

Originally Posted by smontanaro

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?

I have been using www.SpokeCalc.io and a number of their tools for spoke length, tension etc. No cost for the tools I’ve been using and very good docs and explanations too.

[Peter P.]

Where did you learn that by changing the number of crosses would change the tension ratio? I never heard of that.

[smontanaro]

Originally Posted by Peter P.

Where did you learn that by changing the number of crosses would change the tension ratio? I never heard of that.

A friend of mine locally with far more experience building wheels than I will ever have. Sorry, no online reference.

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.

[bikinchris]

Originally Posted by Peter P.

Where did you learn that by changing the number of crosses would change the tension ratio? I never heard of that.

Not crosses, but number of spokes. Campagnolo and others have some wheels with different numbers of spokes on each flange. When you tension the spokes and there are fewer on one side, it will require higher tension to bring the wheel to dish. The Campagnolo G3 have twice as many spokes on the drive side. That offers the chance to make tension from side to side more equal.

[smontanaro]

Originally Posted by bikinchris

Not crosses, but number of spokes.

I totally get that. You're spreading the total load out over fewer spokes. Each spoke will have higher tension. Note that all my wheels are either old or at least "old-compatible." Aside from my Monti Special, nothing's really newer than the early 80s, so using hubs with different numbers of holes on left and right isn't really appropriate.

[Mark McM]

Originally Posted by smontanaro

A friend of mine locally with far more experience building wheels than I will ever have. Sorry, no online reference.

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.

Lacing pattern can change tension balance, but only by a small amount. With only one exception, it's probably not worth changing the lacing pattern to change the tension balance. Varying the number of crossings might change the tension balance by about 1% at most. The singular exception is if all the spokes are laced to the inside or outside of the flanges (which can change tension balance ratio by about +/- 5%), rather than alternating sides of the flange as is usually done.. Note here that it is only practical to lace spokes to one side of the flange for small numbers of spoke crossings - depending on the number of spokes, that might only be 0 (radial) or 1 cross. Also note that on many hubs, lacing the drive side spokes all on the outside of the flange might result in the derailleur contacting the spokes.

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?

[smontanaro]

Originally Posted by Mark McM

Out of curiosity, what are the flange offsets of the hub in question?

Attached is the full detail from Edd for the rear. After a bit more careful measurement of flange distances, I think it's actually 43mm left, 17mm right.

[Mark McM]

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.

[Peter P.]

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.

[Mark McM]

Originally Posted by Peter P.

You want more equal tension for longer lasting wheels-get an off-center rear rim.

Yes, off-center (asymmetric) rims can reduce tension differentials for any dished wheels - multi-gear rear wheels, and disc brake front wheels. But their ability balance tension differential is limited. Asymmetric road rims can have a spoke hole offset of up to about 3mm, and to judge the effect on tension balance of a rear wheel, we can add the spoke offset to the right flange offset and subtract it from the left offset, so in this case the tension balance ratio would change to (17.5 mm + 3mm) / (42.5mm - 3mm ) = 52%. Better, but still quite low.

[smontanaro]

Originally Posted by Mark McM

That is an unusually large left flange offset. 130mm road hubs more typically have a 33-36mm left flange offset.

126mm OLD.

Edit: Also, there's no opportunity to move spacers from right to left, as it's a cartridge bearing hub.

[smontanaro]

Originally Posted by Mark McM

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.

Thanks. 2.0/1.5/2.0 left, 2.0/1.8/2.0 right?

Originally Posted by Mark McM

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.

Thank you! That was what I was looking for.

[smontanaro]

Originally Posted by Peter P.

You want more equal tension for longer lasting wheels-get an off-center rear rim.

What is an off-center rim? Example? Is there anything available in a silver box section rim. Think H+SON TB-14 (current production) or Ambrosio Elite 19 (vintage, early 80s).

[Mark McM]

Originally Posted by smontanaro

Thanks. 2.0/1.5/2.0 left, 2.0/1.8/2.0 right?

Yes, that would be a typical differential spoking combination. If aero spokes are used, then you could use the thinner Sapim CX-Ray spokes on the left and the thicker CX-Sprint spokes on the right.

Originally Posted by smontanaro

What is an off-center rim? Example? Is there anything available in a silver box section rim. Think H+SON TB-14 (current production) or Ambrosio Elite 19 (vintage, early 80s).

An off-center (asymmetric) rim has the spoke holes offset toward one side, for example the Pacenti Forza Asymmetric rim:



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.