Spoking Patterns

[MikewsMITH2]

I am re-rimming and re-spoking a tandem rear hub. It has a built-in drum brake and is of large diameter - 105mm on 700C rims. I have noticed that it was only laced 2x. I am surprised by this. Is/was this standard for large diameter hubs? Should I lace the new rim 2x or go for 3x ? I never experienced a spoke breakage with the old wheel. It has 36 of 2.2mm spokes BTW.

[531colin]

Like rolhoff, the problem is the spokes approach the rim at a funny angle with huge flanges. You can then get fatigue failure where the spokes bend as they enter the nipple. There are 2 approaches;
1) go for 2 cross . Rolhoff specify 2 cross, and there are rims designed to accommodate the spoke angle (even though its less extreme than 3 cross), eg Rigida Andra - I think theres another, I cant remember the name. Its been posted on here somewhere, thats how I know.
2) manually set the bend at the spoke nipple, so spokes are not "stressed" to that shape. Same logic as manually setting the elbow angle at the flange, and "stress releiving" so spokes are not "stressed" ie flexed to shape, which is when they fatigue quickly.

[MikewsMITH2]

Thanks Colin. I have always used Sapim spokes without trouble, so I am thinking of "Sapim Strong" as the ones to go for on this build. The existing spokes are the old "rustless" 2.2mm. The rim I have is as Mavic A319 to match the front.

[531colin]

Sapim strong get my vote for this sort of job. Be pedantic and insist on Sapim nipples, the underside of the head is "mushroom shaped" so they can sit in the rim at an angle. They call them "polyax" nipples or come such.
I need to get out more.........

[PW]

There's a pair of 48 spoke large flange tandem wheels in my shed. Spoked X4 with the spoke line "Adjusted" at the rim. Dog knows how many miles they've done but it's plenty.

[MartinC]

Using 2 cross if the flanges are too large saves you dealing with the angle at the rim. It all gets a bit theoretical though - what's the real downside of bending the spokes at the rim and what's the real downside of lacing 2x? You pays your money and takes your choice.

[PW]

On a rear wheel I'd prefer the spokes as close to tangential as possible. Especially on a tandem with the pulling forces from 2 riders. If 2 cross has worked for you (anyone) in the past that's fine by me, I know the "4X and tweak it" method lasts and I'll stick with it.

[MikewsMITH2]

The 2 x have been on the bike since we bought it new.... In 1980 and never a broken spoke yet! Done plenty of miles sometimes heavily loaded and with only 36 spokes albeit tandem ones. With others using 40 or even 48 spokes perhaps we've been lucky.I'll take Colins advice he's built a few wheels!

[PW]

Colin's methods will work, no bother. That tandem of ours is a Claud Butler Majestic II from the early 80s, (I bought it at the beginning of the miners strike so that's early '83 I think). It carried us and the kids all over the UK and a good bit of northern France, usually with camping gear.

[531colin]

The 2 x have been on the bike since we bought it new.... I'll take Colins advice he's built a few wheels!

That's put me on the spot!!
Actually, Martin C grasped the decision perfectly. Whats the downside of bending spokes at the rim? Well, I'm never sure I have done it spot-on. Bending them at the flange, you have the whole length of the spoke to see if it makes a straight line. Bending at the rim, you are trying to judge if you have a "clean" bend, and if the nipple (which is a lot shorter than a spoke) is in the rim at an acceptable angle. And then you have to guess what effect changing spoke tension will have on the bend you have set.
Whats the downside of 2 cross? Well, tangential spoking "looks right" , but Jobst Brandt says that the pedalling load is shared between so many spokes that the load is insufficient to change the spoke tension enough to make a significant contribution to spoke fatigue. I conclude that 2 cross will support pedalling load adequately....but i will re-visit the section of the book where he considers numbers of crossings, its been a while.

[531colin]

Didnt find a great deal in Brandt. He says "(pedalling) changes in tension are about one tenth of those caused by the weight of the rider on a smooth road." (page 26) Doesnt say what design of wheel this "one tenth" refers to, and says rather little about number of crossings (page 72), this section goes on to deal with "identical and mirror image spoking" , page 74 finishes with "....best to use fewer crossings on the larger flange so that the spokes do not enter the rim at too great an angle."....talking about hub brakes.

[goatwarden]

There's a pair of 48 spoke large flange tandem wheels in my shed. Spoked X4 with the spoke line "Adjusted" at the rim. Dog knows how many miles they've done but it's plenty.

Unfortunately my dog died 10 years ago, so I just asked one of the neighbours' dogs. She wasn't exactly sure but guessed 12,483 miles.

[MikewsMITH2]

The plot thickens. I ran the spoke calculator and the lengths of the old spokes didn't come out for any standard cross pattern. So I dlooked out an old photo:



As you can see the hub was laced one cross, in a symetrical pattern with adajcent spokes with all spoked on the outside of the hub

[531colin]

I think thats probably unusual, if not unique! But the spokes sit nice and square in the rim, dont they?
I wouldnt want to copy that with an alloy hub!

[MikewsMITH2]

I wouldnt want to copy that with an alloy hub!

The hub is alloy! but there is plenty of meat. The spoke holes look elongated, but only on the outside where the spokes have rubbed against the hub. As you can see from the photos, the hub is a very sturdy thing!

I think thats probably unusual, if not unique!

I don't think so... Peugeot made thousands of them in the 70's and 80's. They must've had a good reason for lacing them that way. Peugeot learned a thing or two about bikes in a hundred years. Any ideas why? And would you still go for 2 cross?