3 Cross or 4??? Help me decide

The Moloney's said:

I am building a single speed disc wheel for my 29er. I am going to lace a Paul SS WORD disc hub
into a 36 hole Mavic T520.

I weigh 215 fully loaded and ride mostly rooty, rocky single track.

Which would be a better lacing for me 3 or 4 cross?

3 is easier and just as good.

I weigh 250 and built all my wheels 36 3x. Thousands of miles and no problems.

CRM

One of The Moloney's said:

I am building a single speed disc wheel for my 29er. I am going to lace a Paul SS WORD disc hub
into a 36 hole Mavic T520.

I weigh 215 fully loaded and ride mostly rooty, rocky single track.

Which would be a better lacing for me 3 or 4 cross?

Generally 32 and 36 spoke wheels should be cross 3; 24 & 28 cross 2; 40 cross 4; 48 cross 5.

For unusually large hubs and/or unusually small rims, it is sometimes desirable to go to lower cross
numbers. There is no advantage to going to higher cross numbers.

The issue that this is about is the angle the spoke makes at the rim, and the distance the extended
line of the spoke passes from the axle.

If the cross number is too small, the driving or braking torque loads are not carried so well by the
spokes, and this creates greater stresses on the flanges.

For wheels that don't transmit torque, as with most front wheels, there's no problem with going to
smaller cross numbers, except that it may require oddball spoke lengths that might be hard to find.

If the cross number is too large, the spokes may overlap at the hub, which is an inconvenience in
lacing/replacing them. Worse, the spoke threads will tend to bend at the nipple. (Some rims used to
have the nipple holes angled to prevent this, but most modern bicycle rims don't have this feature.)

You didn't ask, but I don't think the T520 is a great choice for use with a disk brake, because it's
heavier than needed, due to the beefed up braking surfaces it has.

I would also add that I don't think disc brakes make a lot of sense for the rear of a singlespeed.
Unless you're using a frame with an eccentric bottom bracket, axle adjustments will change the
position of the disc with respect to the caliper. Also this would preclude the use of a flip-flop
hub, which is a very desirable feature for a singlespeed.

Hardly anybody rides a singlespeed in conditions that are mountainous enough that front and rear
discs are needed. By all means use a front disc if you want, and don't mind the extra weight, but
you'd be better off with a rim brake in back.

Sheldon "Spox" Brown +------------------------------------------------+
| Man will occasionally stumble over the truth, | but most of the time he will pick himself up |
| and continue on. -- Sir Winston Churchill |
+------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts shipped Worldwide
captainbike.comcaptainbike.comOpen ↗ sheldonbrown.comsheldonbrown.comOpen ↗

The Moloney's said:

I am building a single speed disc wheel for my 29er. I am going to lace a Paul SS WORD disc hub
into a 36 hole Mavic T520.

I weigh 215 fully loaded and ride mostly rooty, rocky single track.

Which would be a better lacing for me 3 or 4 cross?

You can probably use either successfully, but 3x is certainly more common. However, I don't know the
dimensions for your components. Regarding hub and rim spoke angles for some other rather common hub
and rim dimensions, the following provides a feel for what will result:

For 36 hole, 3 cross, 45 mm hub dia, 600 mm rim:

Quoted message said:

Quoted message said:

[hubSpAng, rimSpAng] = spokeangle(36/2, 3, 45, 600)

hubSpAng =
63. 8606
rimSpAng =
64. 8606

For 36 hole, 4 cross, 45 mm hub dia, 600 mm rim:

Quoted message said:

Quoted message said:

[hubSpAng, rimSpAng] = spokeangle(36/2, 4, 45, 600)

hubSpAng =
65. 2798
rimSpAng =
66. 2798

Obviously 4 cross is closer to tangential. As a side note, JB's book _The Bicycle Wheel_ lists a
"spoke angle" in the spoke length formula given at the rear of the text: it is *not* the relevant
spoke angle, although it works perfectly for the purpose of computing spoke length. I have given you
the relevant result here.

For those who give a [censored], the simple MATLAB code I wrote and used is as follows:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

function [hubSpAng, rimSpAng] = spokeangle(No, X, hubRad, rimRad)

%SPOKEANGLE Compute angle of spoke from radial.
%
%
% Syntax: [hubSpAng, rimSpAng] = spokeangle(No, X, hubRad, rimRad)
%
% No := Number of spokes on *one* side of hub.
% X := Number of spoke crosses. hubRad := Radius of hub's spoke hole diameter. rimRad :=
% Radius of rim's spoke hole diameter.
%hubSpAng := Spoke angle from perpendicular to hub circumference (degrees). %rimSpAng := Spoke angle
from perpendicular to rim circumference (degrees).
%

[No, X] = meshgrid(No,X);

hole2holeAngle = 2*pi./No; holeCrossAngle = hole2holeAngle.*X;

a = (cos(holeCrossAngle) - hubRad./rimRad)./sin(holeCrossAngle); hubSpAng = (180/pi)*atan2(1,a);
rimSpAng = (180/pi)*asin(sin(holeCrossAngle)./sqrt(1 + (rimRad./hubRad).^2 -
2*(rimRad./hubRad).*cos(holeCrossAngle)));

Sheldon Brown said:

If the cross number is too small, the driving or braking torque loads are not carried so well by
the spokes, and this creates greater stresses on the flanges.

Re braking loads: Are you referring to fixed-gear and hub (and disc?) braking only?

Quoted message said:

For wheels that don't transmit torque, as with most front wheels, there's no problem with going
to smaller cross numbers, except that it may require oddball spoke lengths that might be hard
to find.

Are 2-crossed spokes more likely to come undone? Or is that just a potential problem for
radial lacing?

Why aren't 2x 32-spoke front wheels more common?

Thanks ~PB

Moloney-<< I am building a single speed disc wheel for my 29er. I am going to lace a Paul SS WORD
disc hub into a 36 hole Mavic T520. >><BR><BR> << Which would be a better lacing for me 3 or 4
cross? >><BR><BR>

3 cross, 4 cross puts too much of the spoke over the hub flange.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote convenzionali costruite eccezionalmente bene"

I said:

Quoted message said:

If the cross number is too small, the driving or braking torque loads are not carried so well by
the spokes, and this creates greater stresses on the flanges.

Pete Biggs asked:

Quoted message said:

Re braking loads: Are you referring to fixed-gear and hub (and disc?) braking only?

No, applies to all hub brakes, including drum- and coaster brakes as well.

Quoted message said:

Quoted message said:

For wheels that don't transmit torque, as with most front wheels, there's no problem with going
to smaller cross numbers, except that it may require oddball spoke lengths that might be hard
to find.

Are 2-crossed spokes more likely to come undone?

No, as long as the spokes are laced where they cross.

Quoted message said:

Or is that just a potential problem for radial lacing?

Radial lacing or un-laced semi-tangent lacing.

Quoted message said:

Why aren't 2x 32-spoke front wheels more common?

They use oddball spoke lengths and offer no advantages over cross 3.

If you're that concerned about weight, radial makes more sense.

Sheldon "Don't Double Cross Me" Brown +-----------------------------------------------+
| Many workmen | Built a huge ball of masonry | Upon a mountaintop. | Then they went to the
| valley below, | And turned to behold their work. | "It is grand," they said; | They loved
| the thing. |
| |
| Of a sudden, it moved: | It came upon them swiftly; | It crushed them all to blood. | But
| some had opportunity to squeal. | --Stephen Crane |
+-----------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts shipped Worldwide
captainbike.comcaptainbike.comOpen ↗ sheldonbrown.comsheldonbrown.comOpen ↗

Sheldon Brown said:

Generally 32 and 36 spoke wheels should be cross 3; 24 & 28 cross 2; 40 cross 4; 48 cross 5.

For unusually large hubs and/or unusually small rims, it is sometimes desirable to go to lower
cross numbers. There is no advantage to going to higher cross numbers.

The issue that this is about is the angle the spoke makes at the rim, and the distance the
extended line of the spoke passes from the axle.

I use cross-4 lacing on 36 hole wheels when I can, because it approaches a perfect tangent
relationship to the spoke hole, giving the highest possible torque capacity. It has a small but
significant advantage over cross-3 lacing in this one respect, which is of extra importance in a
disc-braked wheel.

I just modeled a sample wheel to compare the two patterns. My diagram, using a 45mm spoke hole
circle at the hub and a 610mm ERD on a 36 hole wheel, shows an effective torque arm 11% longer when
laced cross-4 than when laced cross-3. (For comparison, the cross-3 lever is 32% longer than that of
the same wheel laced cross-2.) The angle of incidence at the rim is barely affected, the x3 spoke
inserting 3.8 degrees from perpendicular and the x4 spoke only 4.2 degrees from perpendicular.

That 11% improvement in torque arm length for a cross-4 wheel may be small, but it comes at no
significant cost, except that it is slightly more difficult to lace up and a slightly more elaborate
operation to replace a broken spoke. These issues are mitigated by using high-flange hubs, which
have an even more pronounced effect on the wheel's capacity to translate small spoke tension
fluctuations into large torques.

It does not seem like torque resistance is a critical property for a wheel, but my extreme-case
calculations predict a per-spoke tension fluctuation of +/-293 lbs! (That's a 300lb rider standing
on a 190mm crank with a 24t ring pulling a 34t sprocket, with a 36 spoke rear wheel laced cross-2 on
a 45mm spoke circle hub. I assume a thin-center hub where all the torque load is borne by the right
side spokes.)

300lb pedal load x .623ft crank = 186.89lbft

186.89lbft x (34/24) gear reduction = 264.76lbft

187.76lbft / 18 drive side spokes = 14.71lbft per spoke

188.71lbft / .05025ft spoke lever arm = 292.7 lbs

Chalo Colina

Qui si parla Campagnolo said:

Moloney-<< I am building a single speed disc wheel for my 29er. I am going to lace a Paul SS WORD
disc hub into a 36 hole Mavic T520. >><BR><BR> << Which would be a better lacing for me 3 or 4
cross? >><BR><BR>

3 cross, 4 cross puts too much of the spoke over the hub flange.

I've done 4x on 36 hole wheels with no significant problem. The overlap of the flange doesn't much
matter as best I can tell. Only getting on one spoke on top of the head of another is a problem if
replacement becomes necessary. Still, I tend to do 3x for 36 hole.

Some say that 3 cross is stiffer and gives a harsher ride, because the spokes are shorter. But the
only difference I've noticed is they are easier to lace.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": geocities.comczcornerOpen ↗

It makes no difference in the real world. 4 Cross allows the spoke to take a longer exit tangent
through the hub. This might have been important way back when flanges were much thinner than todays
to prevent the spoke fracturing the flange. But nowadays with better materials than ever, either
will work fine. The quality of the build will make a far bigger difference in strength than 3 vs 4
cross, which I seriously doubt could be measured without a laboratory. Find a good builder first,
use quality DT spokes and enjoy the ride.