Question:
I have just got a rear wheel back from my LBS after having a new spoke
fitted, and to have the whole thing trued. But "listening" to the tension of
the spokes, they do not seem to have much tension. How much tension should a
spoke have? Obviously the tension on each spoke needs to be roughly
equivalent, but what is the test to make sure they are the correct tension?
I know for all you wheel builders out there this is a no-brainer, but I'm
trying to bridge my knowledge gap : )
Answer:
The maximum which the rim will stand is the answer, but I know it doesn't
help you much!
Generally, you keep increasing the tension until either the nipples don't
turn any more or until the rim stays deformed (into a 'pringle shape') after
you stress-relieve it. This is not difficult to do yourself, but read Jobst
Brandt's book first.
what happens when you cycle is that the bottom spoke detensions. As long as
there's still tension in it at the bottom it will not unscrew. If there
isn't it will.
The correct tension depends on the load then.
As much as possible without deforming the wheel is the best. This makes the
strongest wheel.
The block-side spokes are the tight ones - the other side will always be
quite a lot slacker because of the wheel dishing.
When I started building my own wheels, I used to get them as tight as
possible (even to the extent of having a butted spoke snap in the middle),
but I found that I was getting problems with cracks around the eyelets in
the rim, and the eyelets started to pull through after a while.
Another symptom of excessive tightness is very small adjustments chasing a
wobble round the rim.
What I do now is build them so I can only just push the spokes apart where
they cross (3x pattern) - fingers round one spoke, push on the other with
the thumb. If I try to hold them apart, it's definitely uncomfortable where
the spoke presses on the thumb.
Loading the wheel only reduces the tension of the spokes. Think of pushing
down on the hub and you reduce the tension in the spokes underneath. Its
known as the wheel standing on its spokes after the description in Jobst
Brandt's book The Bicycle Wheel.
Many of the problems with spokes are with too little tension so that under
dynamic loading the spoke tension goes to zero allowing the nipples to
unscrew etc.
