SelfPropelledDevo
In this case we are using a rear MAVIC SpeedCity wheel.
Difficulty: Advanced
Tools:
1. Truing stand
2. Dishing tool
3. Spoke wrench(s)
4. Tensiometer
Time: 5 to 10 minutes. (when you are good at it)
Spokes are STRONG!
when they break they pull apart like taffy
The hub hangs in the rim.
Spokes are strong when pulling.
When you have a plain spoke in your hand, you can easily push it out of shape, but if you try to pull it, it is VERY STRONG. It behaves sort of like rope, string, etc. In fact, when you think of spokes, think along the lines of piano wire tension.
The rim has its own strength too. Its shape, unlaced, should be true. When a hub is laced to the rim, the spokes start to pull, and tension builds up in the hub flanges, eyelets, spokes, nipples, etc. At first the spokes are loose in the eyelets of the rim when you first lace up the wheel. (Building a wheel) You bring all the spoke nipples to the rim eyelets with a nipple driver, at this point, it is referred to as “Zero”. That is the spokes are slightly tightened up enough to seat the nipples in the rim eyelets, there is little to no tension in the spokes. (and the rim should be pretty straight in the stand)
Each spoke nipple is then tightened up using a spoke wrench. Counter clockwise 1/2 turn increments is what you really should use at first. This small amount (at this stage) applies light tension. As you make your way around the wheel think of it as adding “layers of tension” to the wheel. Every so often you stop to dis-stress the spokes, and let things get a chance to seat more if needed.
On to TRUING. There are two sides to a wheel. The Drive side and the Non-drive side. Spokes radiate out from the hub on both, Drive and Non-drive sides. When the wheel is out of true, in this case lets say it pulls, or wobbles to the left (non-drive side). Basically what you need to do is pull the rim to the right (drive side) at the point where its out of true. And the way you do that is to use the correct spoke wrench on the spoke nipples and make the adjustments.
Typically what you would do in a case like this, is to pull the rim to the drive side by tightening the drive side spoke nipple at the wobble and possibly loosen the non-drive side a bit by turning the spoke wrench clockwise. This pulls the rim to the drive side, and releases tension/distance on the spokes of the non-drive side. Hopefully the rim pulls into shape.
(On Tension)
By all means, if the above was actual, and the wheel had been properly built up with uniform spoke tension, and lets say i did a bunny hop up a curb, but actually hit the curb, and now my wheel is out of wack (true). What the actual damage is that the rim is actually bent. To now make that bent rim (bent wheel) straight, and behave like a true wheel, we have to pull the rim back into shape. But pulling on spokes adds tension. However you can often let some tension loose on one side, and pull it tighter towards the other. A give and take of sorts. The wheel will NEVER be the same again after something like this. In order to get the wheel straight, the tension is now not uniform. That means some spokes have significantly more tension than others. This wheel is now prone to going out of true. Why?
When a wheel is first built the rim is straight and spoke tension has been uniformly applied. The tension keeps the spokes in place. Remember that the hub hangs in the rim by the spokes. If a spoke is loose it is easily pushed out of shape. Repeating this flexing action, a spoke does not like! Typically they will crack, then snap, due to the flex cycle. It happens almost instantly, and all you hear is a tang from your wheel. When you flex a spoke back and forth, it will fail. When you pull on a spoke it is incredibly strong. They take something like 150psi, and it starts to pull apart like taffy. A set of spokes will easily collapse a rim in a wheel set when you tighten it to that extent. Often i have seen spoke nipples pull out of rim eyelets.
When we hit all those little pot holes, and just thru daily life, wheels take a beating. They are subjected to all sorts of forces. they have to pull, brake, keep things aligned, and go thru a myriad of situations. All that use usually makes a rim start to break down at some weak spot, and remember this is all dynamic, that is its spinning and under load! The rim has some strength, but what we are really depending on is uniform spoke tension.
Saturday, June 16, 2007
How to true a wheel.
