In my last blog post I covered how to lace up a wheel assembly with new spokes. This week I’ll discuss how to properly true the rim. Truing the rim is actually not too difficult. Once you understand the interaction between the spokes and rim, you will make quick work of the job.
To get started a truing stand of sorts needs to be set up. This doesn’t have to be anything special and I used a bench vice, adjuster block, rear axle, spacers, a series of old bearings and washers, and the axle nut. The reason I went to the trouble of clamping the hub in place was to eliminate any possibility of the hub sliding back and forth on the rim, which would make my truing efforts difficult.
This is by no means the only way to create temporary truing stand and you can use your imagination to come up with alternatives. Temporarily installing the wheel back into the swingarm may work equally well if you don’t have a bench vice.
Next, some sort of gauge will be needed so the amount of runout can be seen. I used a dial indicator attached to a magnetic base, however more simple solutions could easily be fabricated.
It isn’t absolutely necessary to measure runout, especially right away when major adjustments may need to be made. Instead you only need to see how the gap between the end of the pointer and rim changes as the wheel rotates. A coat hanger, piece of welding rod, or even a pencil could all be used to the same effect as the indicator shown.
Axial (side to side) runout will be corrected first. Here you can see there is a noticeable difference in gap size between the rim and pointer through a full revolution of the rim.
The goal is to tweak the tension in the spokes so that the gap between the rim and pointer is even as the rim is rotated.
To do this the gap can either be increased or decreased depending on which spokes are tightened or loosened. To decrease the gap, tighten the spokes originating on the side of the rim where you want the gap to decrease. In the previous photo I’m tightening the right side spokes, and in doing so I am pulling the rim to the right. An ⅛ to ¼ turn of the nipple is enough to induce a change. For the given area of the rim that must be pulled over, evenly tighten at least three of the surrounding spokes on the side being pulled. If the rim needs to shift a lot, loosen the opposite side spokes the same amount you have tightened the pull side spokes. This will help keep even tension on all spokes and help to shift the rim.
The process of tightening and loosening the spokes to pull the rim from side to side can be performed at all the high and low points surrounding the rim. Continue to turn and rotate the rim around until the gap between the rim and pointer evens out. Some areas may require tightening the spokes and pulling the rim one way while other areas may need to be loosened to allow the rim to move back the opposite way. Take your time and make small changes as you go. As I mentioned before, it doesn’t take much to see a significant change in rim location as the spokes are tensioned.
As the rim is fine tuned for side to side runout, the pointer can be moved closer to reduce the gap. Reducing the gap as the rim is trued will make it easier to see smaller differences in runout. To really fine tune things I like to use a dial indicator, setting the contact point up on the outer edge of the rim. Again, this isn’t absolutely necessary and similar accuracy could be achieved with a simple pointer.
Here I’ve snapped photos of the high and low points on the rim. The total runout is the difference between the high and low points. In the left picture the needle is 0.0075” (0.19mm) to the left of my zeroed point. In the righthand picture the needle is 0.008” (0.20mm) to the right of the zero. This gives me a total runout of 0.0155” (0.39mm). Most service manuals suggest a max runout of 0.079” (2mm) so I’m well within spec! Quite frankly I was very pleased to get the rim to 0.0155” since the rim is old and slightly dinged up.
The rim I was working on is centered on the hub. Some rims will be offset and it will be more important to pay attention to the relationship between the edge of the rim and a feature on the hub (usually the brake disc machined surface or the machined surface for the sprocket). Your service manual will provide specs for measurement points and specify how much offset should be present. Setting the offset correctly is important because if the offset is off, the front or rear wheel will not be inline with the other wheel. This can make the bike's handling very interesting! I don’t think a little misalignment is too noticeable on dirt, but it is definitely a problem on asphalt.
A straightedge can be used to measure from the indicated surface, outer edge of the sprocket, or brake disc to the edge of the rim. If measuring off the sprocket or brake disc, you’ll need to subtract the thickness of the sprocket or disc from your measurement.
If the rim is not quite positioned right after all the side to side runout has been corrected, it can be shifted at this time. To pull the rim one way or the other, simply evenly tighten all the spokes on the side you are trying to pull the rim to. The opposite side spokes can also be loosened to help allow the rim to shift over. Once the rim is set where it needs to be, half the battle is over!
Next, the radial runout must be corrected. To do this move the pointer so that it sits past the outer edge of the rim.
The gap between the pointer and outer edge of the rim will be monitored and tweaked to achieve evenness throughout the rotation of the rim.
This time to induce change in runout, all the surrounding spokes in the area will either be tightened or loosened evenly in unison. To increase the gap, as I’m doing in the following photo, all the spokes are tightened which pulls the rim inward, enlarging the gap between the pointer and edge of the rim.
To decrease the gap in a specific area all the spokes in that area can be loosened allowing the rim to expand outward towards the pointer. Just like with side to side runout corrections, the nipples only need to be turned an ⅛ to a ¼ turn to make noticeable changes in the gap.
As long as all spokes in the affected area are tightened or loosened evenly, the side to side runout will not be affected. Slowly rotate the rim and make the necessary tweaks until the gap between the edge of the rim and pointer is close to the same as the rim rotates around. The pointer can be moved closer and closer to refine the roundness of the rim. The surface of my rim was too beat up to take accurate measurements so I simply relied on eyeballing the gap to set its roundness.
Once the rim has been trued both axially and radially, the spokes will still be relatively loose. The spokes will all need to be tightened gradually and evenly so that all the efforts of truing the rim are not wasted. Since the majority of rims are either 32 or 36 spoke rims every 4th spoke around the rim can be tightened. This results in an even 8 or 9 step pattern which is repeated four times to tighten all the spokes. First all the red spokes are tightened, then the greens, yellows, and finally blues. Tighten each spoke ¼ turn at a time.
Alternatively, forum member ballisticexchris, suggested a pattern where every third spoke is tightened. This would allow the tensioning of both sides of the rim within the same revolution of the wheel. I've always had good results with the pattern I've outlined but believe his suggested pattern will work equally well and is another option for you to use.
As the spokes are tightened, not surprisingly, the nipples will become harder and harder to turn. The evenness of the spoke tension can be checked by tapping the end of the wrench against the center of the spoke. The spokes will emit a ringing sound and the pitch will be different for spokes which aren’t the same tightness. Continue to work your way around the rim gradually tightening the nipples until all the spokes are similarly tensioned.
Next, use your hand to squeeze the spokes which are parallel to each other together. Squeeze all the spokes evenly around the rim. Squeezing the spokes will help gauge the tension, ensure the heads are fully seated, and help relieve stress built up in the spokes.
After squeezing the spokes together, check the tension in the spokes one final time. Most spokes should only be tightened up to 6Nm and the rim I was working on called for 2.2Nm of torque. A spoke torque wrench is the appropriate tool to use to set the final torque of all the spokes, however I didn’t have one on hand and some of you may not either. Instead I based the final spoke tension on how the new spokes felt in relation to a previously laced rim. This method worked okay, but it is always best to use the right tool for the job.
After you’ve finished tightening all the spokes it is never a bad idea to check runout both axially and radially one final time to confirm the rim hasn’t shifted. As long as the spokes were tightened evenly, changes in runout should not be an issue. Once you have checked runout one last time you are all set to install a new rim strip and put on the tire.
I hope you enjoyed this two part series on building and truing rims. Now that you have the info to feel confident building your own wheels from here on out, and are able to save some cash in doing so, go for it!
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If you have tips and tricks pertaining to wheel building, I’d enjoy hearing them. Please leave a comment below!
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