How is the finishing stage of truing a laced wheel improved by adjusting spokes in groups of 4?
Note: This pertains to laced, not radially spoked, wheels
because a radial spoke applies no torque to its hub.


When truing a laced wheel, adjusting spokes in groups of 4
eliminates distortional side effects that would otherwise be relayed by
hub&nbsp;torque to all other spokes.

Hub torque is a turning force between hub and rim,
generally recognized in two main forms
where the rim has a tire that contacts the road.


Pedaling produces a driving torque on the rear hub.
A disc or drum brake produces a braking torque on either hub.


This is explained in
The Bicycle Wheel, Third Edition, by Jobst Brandt,
beginning with the section Torsional Loads on page&nbsp;22.
Three pages later,
Figure 11 exaggeratedly displays a typical complex of rim distortions
produced by hub torque
as half of the spokes experience increased tension
while the other half experience relaxation.


  Torsional Loads
  &thinsp;&middot; &middot; &middot;
  Spokes [.&hairsp;.&hairsp;.]
  transmit torque from the hub to the rim by becoming tighter and looser.
  &thinsp;&middot; &middot; &middot;
  


The converse is also true:
spokes&rsquo; tensions transmit torque from rim to hub.
Although a wheel being trued has no road to fight against,
its hub is nonetheless torqued relative to the rim,
by each and every spoke.

Spokes are commonly adjusted in rim-adjacent pairs
so that lateral or radial corrections
do not become, respectively, radial or lateral distortions.
This works well near such a pair spokes but the adjustment
often changes their combined hub torque enough to distort the rim elsewhere.
One example is a lateral rim adjustment made
by tightening one spoke while loosening its neighbor.



The preferred adjustment with four spokes includes
two additional rim-adjacent neighbors.



As spokes that are two holes apart on the rim
connect to symmetrically placed holes on the same flange,
equal adjustment of those spokes produces no combined change in rim torque.
Adjusting each spoke in this 4-wise group
half as much as its corresponding spoke in the pairwise adjustment
produces the originally intended rim correction,
as would be hoped, but without creating new errors elsewhere.