Wheels are perhaps one of the most complex parts of cycling in that they are the contact between the rider and the ground or pavement and can be considered the best upgrade a bicycle can have. Properly trued and tensioned wheels at all levels greatly improve the quality of the ride and the longevity of their peak performance. Attention to detail, patience, and practice will provide you with worry free operation time and time again. In the rest of the article, I’ll be referring the true and tension of a wheel as simply wheel truing because both are necessary to keep a wheel straight and rolling correctly.
I believe that anyone can true their own wheels (except for some tubulars and several specific racing wheels) with a bit of guidance and attention to detail. Taking the time to check your wheels after long rides and on a regular basis will allow you to minimize the amount of truing needed. A wheel can only be trued so many times before there are no more threads left to tighten on the spokes. Below is a diagram of a section of rim, a spoke, and a spoke nipple.
In this diagram, the spoke is threaded into the spoke nipple, which is anchored by the small lip on the inside of the rim. There are about 10mm of threads on the majority of spokes. Usually, 5-8mm of threads are threaded into the spoke nipple, based on correct spoke length calculation. This leaves several millimeters of thread to be tightened during the life of the rim and spokes for truing.
Tightening the spoke nipple will guide and pull the rim to the left or right laterally as well as pull it inward towards the hub. A diagram below illustrates this.
In this diagram, several of the elements were recreated from the first diagram (the spoke, spoke nipple, and rim). This is a cross-section of the rim to show how tightening and loosening the spokes will cause the rim to move to the right or left. Notice that the spoke and spoke nipple does not anchor to the rim at a direction 90 degrees, but at an angle because of the fact that the hub (the center part of the wheel) is wider than the rim. If you tighten the spoke from the spoke nipple in this diagram, the rim will be pulled to the left. If you loosen the spoke from the spoke nipple, the rim will move to the right. This is how, over the course of the rim and all the spokes, that the rim can be straightened and thus, trued.
Now that the concepts are a little clearer, we can then focus on how much to tighten and loosen the spokes. Once a wheel is built the tension of all the spokes should be relatively even. Factory built wheels tighten all spokes to a specific tension, causing the rim to usually be slightly out of true once it gets to the shop from a distributor. The reason that the rim is not true from every spoke being at the exact same tension is because of all the variables in the wheel add up and even high quality parts have small imperfections and variations in machining and manufacturing, summarized by the term, tolerance. Remember that term because it will come up later.
When truing a wheel, it is wise to make small adjustments each time until the rim is straight (1/8th turns to 1/2 turns). Never just crank down on one spoke and tighten it until the rim straightens. This will cause uneven tension of the wheel, which will lead to spokes breaking and the rim to develop a ‘set’ and a shorter lifespan. Spin the wheel and notice how much the rim moves side to side and settle on the worst sections first. If you see the rim move to the left or right over a section, take note of how many spokes pass throughout the bend. Find the worst part of the bend and tighten that spoke about a half turn and then the spokes on either side coming from the same side of the hub. Tighten those spoke less and less the farther it gets from the spoke you first tightened a half turn, tightening less as the bend recedes. Lightly squeeze spokes with your hands and spin the wheel in between truing to settle the adjustments. This ‘shares the load’ between the spokes to straighten that section of the rim and allows the tensions to be gradually increased. The spokes in a wheel do not work individually as much as being a team. All must help to share the load of the rider on a bike.
Earlier I mentioned that spokes could also be loosened. This is only really acceptable in very small amounts and as a second option after tightening spokes. Loosening decreases tension in the wheel, which can also lead to spokes breaking and less threads engaged in the spoke nipple. In particularly difficult sections of a rim, tightening and loosening is used to correct a bend, but only with practice and experience over time. Even with this basic tutorial to help you better understand how a wheel is trued, your first few wheel truings will be a little frustrating. Know that as you progress and true more wheels, you will begin to understand how much you must tighten a section of spokes to eliminate bends in the rim. Lastly, sharp bends in a rim are nearly incurable and you will notice that one or two spokes must be tightened by a large amount to even get the wheel ‘mostly’ true. If this is the case, the rim may need to be replaced and new spokes. The spoke itself is very very strong and can easily hold 300lbs hanging from its end without much wear. This being said, the spoke’s main enemy is uneven tension and the fact that there are only so many threads on the spoke’s end to tighten.
In summary, remember these two things. No spoke works alone and thus, tighten groups of spokes to share the load small increments at a time. The tolerance of machines and production allow a wheel to be only so true. Low quality wheels can be trued to moderate expectation and high quality wheels can be trued to high expectation. This is the difference in tolerances of machining.
Feel free to email or message me regarding any questions you might have. People have written many books on this subject and I could continually talk to you about wheel theory all day. Hopefully this article will help you to better understand wheels, how they are adjusted, and your confidence in being your own bicycle mechanic. Thanks for reading. Monday night, I’ll be posting Part One of the Specialized Turbo S Long Term Review and what things I have come to learn about working on them, adjusting the electronics, and general knowledge as far as how the technology is progressing.