What is a strain gauge?

By definition, it's a device used to measure tension. However, searching for this term in Wikipedia, for example, reveals primarily information about electronic strain gauges—electrical systems that measure tension based on differences in resistivity or resistance. In a bicycle repair shop, much simpler tools are used. A bicycle strain gauge measures the tension of individual spokes using three pressure points and a spring. Every self-respecting repair shop should have at least one such tool. Why? Because when used correctly (which is unfortunately not always the case), it significantly improves the quality of the laced wheels. It allows for uniform tension, and therefore a durable and stiff wheel. Read about braiding rings

The principle of operation of a strain gauge

Above all, a strain gauge must be rigid to prevent deformation from affecting the measurement result. For this reason, thick, cut aluminum or carbon fiber sheet is typically used. All operate on a similar principle. Two support points are fixed, and one between them moves on a spring and is connected to a pointer. The spoke is inserted between the support points so that the moving point causes it to deform. The amount of deformation depends on the spoke tension and is measured by the tension of the spring connected to the pointer. Simple? Not entirely. The shape, thickness, and material of the spoke are also crucial. Therefore, the result displayed on the device should be multiplied by the appropriate factor provided in the manufacturer's table. Only then will the tension in newtons be obtained. While there are models with electronic displays on the market, their operating principle is the same. Only the method of displaying the result differs, though it's undeniable that high-end tools are more accurate. However, it's worth remembering that due to spoke manufacturing tolerances, measurement error is around 10%. Furthermore, due to rim imperfections, perfectly even spoke tension is impossible (at least not on a straight wheel). Typically, a maximum difference between spokes is assumed to be around 5-10%.

Why is the strain gauge so important?

Of course, you can build a functioning wheel without one – after all, mechanics have been doing it this way for decades. However, there's no denying that the results with a tension gauge are much better, and corrections after spoke alignment are usually cosmetic. Moreover, for high-end wheels, especially carbon rims and butted spokes, it's a must-have. It allows you to assemble a wheel from components with the exact tensions at which they will perform best. It certainly won't replace skill – without knowledge and experience, it's useless. However, in the hands of a skilled wheelbuilder, it will allow you to create much better wheels and get the most out of your parts. It's also a tool that aids self-discipline and protects you from wishful thinking. There's no such thing as "it looks good to me." You can't argue with measurement, however frustrating it may be. Would I recommend a strain gauge to amateurs? Probably not. It's a tool that only someone who's built dozens of wheels and is proficient in using it will benefit from. Without a feel for the wheel and experience with its behavior during centering, it will only add to the complexity. However, I advise avoiding any repair shop that doesn't have a strain gauge.