Wheel building

[ian peacock]

Good moaning, I am about to rebuild a rear wheel which has a 27" Weinmann rim on an Airlight L/F hub. Currently it has 4X spokes: why did they do this? I intend to rebuild it 3X with new spokes (the originals are chrome and in poor condition).

[Mick F]

Four-cross is usually for extra strength for heavy work and touring.
Three-cross would be fine for normal riding.

[Jamesh]

I've done two wheels 2 cross and they gave been fine...

3/4 cross for touring / tandems.

[531colin]

......... 4X spokes: why did they do this? .........

Take a look at the existing wheel.
40 spoke 4 cross means the spokes are pretty much exactly tangential to the hub flange, so adjacent spokes are pulling at the hub flange in opposite directions.
Contrast this with radial spoking, where adjacent spokes are pulling radially at the hub flange....and from time to time you will see a radial spoked wheel where the spokes have succeeded in pulling a bit off the hub flange, with predictable results.

Also, if you build "one side at a time" rather than "putting all the inbound spokes in and twisting the hub", then 40H 4x is a logical geometric pattern....the (near) parallel pairs of spokes form a cross.....we used to call this "Maltese cross" lacing.
....the old spoke numbers.....40 rear, 32 front.... are "numbers divisible by 8".....8 is your Maltese cross

[thirdcrank]

I'm no wheelbuilder but Colin's post has encouraged me to mention that a large flange hub makes his explanation "even more so." (AIUI)

[531colin]

I'm no wheelbuilder but Colin's post has encouraged me to mention that a large flange hub makes his explanation "even more so." (AIUI)

And Airlights are pretty big!

[rogerzilla]

x4 is normal for 40 spokes or more. It is a bit iffy for 36, as the spoke angle at the rim is way off perpendicular.

Those Airlite hubs sometimes have loose flanges when dismantled. They won't fall apart when laced up - spoke tension keeps them very well clamped together - but you need to ensure the spoke holes are offset properly before you build the wheel. Otherwise it will be a right pain.

[ian peacock]

Thanks for all those replies, they have been very helpful. I shall have a go at building 4X. I have built lots of wheels in the past, but always 3X.

[531colin]

x4 is normal for 40 spokes or more. It is a bit iffy for 36, as the spoke angle at the rim is way off perpendicular.........

Not sure about that.
There is a theory that you can reduce the differential in spoke tension in a dished wheel by building with fewer crosses driveside than non-driveside; fewer crosses get a better "bracing angle" of the spokes, because with fewer crosses the spokes come from further out on the flange....(ie closer to the rim......its difficult to explain....with fully tangential spoking, the near parallel pairs come from diametrically opposite sides of the flange, ie at the level of the axle.....with fewer crosses, ie less than tangential, the near parallel pairs of spokes originate closer together in the hub flange, so higher up or further out than the axle)
So I duly built a 36H 700c wheel with 2 cross driveside and 4 cross non-driveside, on a 6 bolt disc hub (which is "large flange" in old terminology). Its impossible to get a really good impression from a picture, but I took one anyway.....

IMG_5608 by 531colin, on Flickr

Suffice it to say I don't think there is a dramatic difference between 2 and 4 cross sides in terms of the angle at which the spokes approach the rim.
(and if there was an improvement in the differential spoke tension, it was too subtle for me to measure with a Park tension gauge)

Just for comparison, a picture of a 2 cross 36 spoke 700c Rohloff wheel. I think the spoke nipples here are at a worse angle than the 36 hole 4 cross, because the hub is really big.

IMG_5609 by 531colin, on Flickr

[531colin]

OK, so heres the thing I was struggling with yesterday.....

36 spoke 700c wheel laced 3 cross; distance between the heads of 2 spokes forming a near-parallel pair is 57mm
Radial spoke has the best angle with the rim, 90 degrees.
So these spokes are 28.5mm away from that.

IMG_5610 by 531colin, on Flickr

36 spoke 700c wheel laced 4 cross; distance between heads of spokes as above is 60mm
so these spokes are 30mm away from a radial spoke.

IMG_5614 by 531colin, on Flickr

1.5mm over the length of a spoke makes no great difference to the angle between the nipple and the rim

On a small flange hub, the actual distances will be smaller, but I imagine the ratios between them will be the same.
36 spoke 4 cross on a small flange hub might risk some interference between adjacent spokes at the flange.

[SimonCelsa]

Just for comparison, a picture of a 2 cross 36 spoke 700c Rohloff wheel. I think the spoke nipples here are at a worse angle than the 36 hole 4 cross, because the hub is really big.

IMG_5609 by 531colin, on Flickr

Bejesus!! I wouldn't be happy with that wheel. I would take that apart and try again.

[531colin]

.............
Bejesus!! I wouldn't be happy with that wheel. I would take that apart and try again.

Usual caveat....impossible to get a representative photo.
I think I have the camera at an angle (not square to the axle/not parallel to the rim) so some nipples present an exaggerated angle. (and some a reduced angle)
but its 2 cross, which is what Rohloff say, and I have made sure the spokes are "set" (ie bent) to that bend, not "stressed" (ie flexed) to the bend. (Fatigue is much quicker when the inevitable repeated stress cycles caused by riding the thing are superimposed on an already stressed spoke compared to a spoke with a set.)
I couldn't get a rim with offset spoke holes at the time. Thorn now build 1 cross, I didn't know that at the time, either!

[rogerzilla]

x1 can play havoc with spoke calculators, as can radial. The heads-out spokes take a significantly shorter path to the rim when there are no crossings.

[home]

I think the spoke nipples here are at a worse angle than the 36 hole 4 cross, because the hub is really big.

Would cupped washers on the inside of the rim help? I though because of the size of the hub Rohloff recommended surprising few spokes/cross over while claiming it was strong enough.

I note your rims have eyelets. What's the low down as far as filing poor machine holes in order to get better spoke angles? I wouldn't be happy with such a tight bend.

(Having written that, allow me to confess. In the past, using a rim that the holes had not been drilled at an angle, I have used both a cupped washer on the inside and manually filed the holes a bit to allow the nipples to run inline with the spoke. Never read about it. The idea of washer was to make up for any potential variance by spreading the load. It's a big problem on 20" wheels with 3 crosses.).

[531colin]

A bend at the nipple is only a problem if the spokes fatigue and fail at the bend.
The usual "correction" is to "set" the bend, ie take the spoke past yield point so that the bend is permanent, the spoke is set at that angle, not flexed to the angle. (rapid fatigue occurs in a bit of spoke which is flexed to an angle, because the stress of changes in tension every revolution are superimposed on top of the static stress of a being stressed to shape; this is why spokes fail at the elbow bend at the hub flange unless they are set to the proper angle and stress-relieved at that angle)
It remains to be seen whether or not I succeeded in setting my spokes bend; although at 75 years and 70 Kg I'm not really a harsh test of a wheel!
I built 2 cross because thats what Rohloff say; their flanges don't have a good track record.
Thorn now build 1 cross, I understand, with all the spokes from the same side of the flange.
I have never tried cup washers, I can't envisage them being much help...... the nipple is domed and the rim is cupped already?
Never tried filing the holes either, it will work only if its the bore which limits the angle ?
Sapim reckon their "polyax" nipples give more articulation.
"Brucey" I think recommended "tweaking" the rim eyelets to a better angle using a bit of thin rod/thick wire in the hole....Seemed a bit difficult to control to me.
Why not build 20" wheels 2 cross? Or 1 cross?
I don't think torque is a problem.....i have just typed all that out here viewtopic.php?t=151833