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Your Custom Wheel with a Hub Dynamo

A hub dynamo provides power for lights and charging smartphones and GPS on the bike. We’ll show you what to look out for when building a dynamo wheel.

Whether you want to equip your everyday bike with lighting or want to have a self-sufficient power supply on rides and multi-day tours, there are many reasons to have a front wheel with a hub dynamo. It’s always a relief when the lighting on your commuter bike just works whenever you need it. Charging battery lighting is a thing of the past, and so are those unfortunate moments on a ride when you realise that you had forgotten to do it. A hub dynamo on your bike can also be a real asset when bikepacking. In addition to providing light across long distances, it can power your navigation system and smartphone and saves you from constantly searching for power outlets. However, why lace it yourself when you could order a ready-made wheel? There are arguments in favour of custom wheels in general: in addition to the fun of DIY, the process of creating them can fulfil very specific requirements or simply serve to further individualise your bike. We have compiled ten good reasons for custom wheel building in a special article. When installing a hub dynamo, you probably only want to change out the front wheel and not the whole wheelset. Building a custom wheel gives you the advantage of creating a match for your rear wheel – namely something with the same rim and the same nipples and spokes. We’ll go over what you should look out for when it comes to hub dynamos.

Choosing the right hub dynamo

When it comes to hub dynamos, there are more aspects to consider than with conventional hubs. Power output is an important feature, and all models produce a voltage of six volts – however, they differ in what power they deliver. Until a few years ago, the StVZO stipulated a nominal voltage of six volts and a nominal power of three watts, and practically all dynamos available in Germany met these criteria. The value was reasonable to operate halogen lighting. Since the strict regulation from the StVZO has been dropped and efficient LED lamps have replaced other light sources, there are also hub dynamo models with a lower output of 1.5 or 2.4 watts, which are lighter and rotate with less resistance. Whether this is a sensible option for you also depends on the light you choose. There are models that reach their maximum light output with 1.5 watts and those that can only be fully exploited with a three-watt dynamo. For everyday use in the city, 1.5-watt combinations are adequate. For cross-country trips or passages in the forest where maximum light output is important – even at low speeds – we recommend three watts. Since the rotational frequency at the same speed depends on the wheel size, there are hub dynamos that are optimised for this purpose – for folding bikes, for example. Most of them are constructed for universal use, but it is always worth taking a careful look at the description.

Important key figures about hubs

Besides the power output, hub dynamos differ in aspects that you probably already know from normal hubs: the number of holes determines how many spokes you can use. Most of the time, this is already predetermined by the rim. Generally speaking, more spokes make for a stronger and more durable wheel. Hubs with a low number of holes are useful for applications with lower loads and for small wheels – for example folding bikes. Over locknut dimensions and axle type are important factors that are specified by your fork. For the brake system you can choose between rim brakes and disc brakes. When deciding between six-bolt disc and centre lock, we recommend choosing the same system as on the rear wheel. If you are not only putting together a new front wheel, but rather a complete wheelset, you have to weigh things up. Six-bolt hubs have the advantage that you can choose from a wider range of brake rotors. They are mounted with six T25 Torx screws each, and the matching key can even be found on most multi-tools. Center lock has the advantage of significantly faster and easier mounting and dismounting. However, you need the right cassette removal tool: the rotor is placed on a gearing on the hub body and screwed on with a lockring, which has either internal or external gearing. With the help of adapters, six-bolt rotors can also be fitted to centre lock hubs and vice versa.

Lacing a hub dynamo differs only slightly from lacing with a classic hub. The biggest difference lies in the required spoke length.
Lacing a hub dynamo differs only slightly from lacing with a classic hub. The biggest difference lies in the required spoke length.

Lacing a hub dynamo differs only slightly from lacing with a classic hub. The biggest difference lies in the required spoke length. © bc GmbH

Rims and spokes for hub dynamos

When choosing a rim, there are several factors to consider depending on the intended use, rider weight and riding style. As previously mentioned, it is a good idea to build a custom front wheel with the same rim as on your existing rear wheel. Of course, this is not absolutely mandatory: many intentionally install lighter or narrower rims from the same manufacturer on the front wheel, which visually match the rear wheel but are designed for the lower loads at the front. If you want to build a complete wheelset, you have the freedom to choose. The brake system (rim brake or disc) and the diameter are basically determined by your frame. When deciding between a carbon or aluminium rim, you should consider not only your budget but also how much you value stiffness and weight. Carbon rims are usually lighter or stiffer for the same weight, while aluminium rims are cheaper and can sometimes also be more comfortable. Also, the rim width should match the tyre width. Both tyre and rim manufacturers provide helpful advice on this front. You can find detailed tips on choosing the right rim here. Regarding the spokes, the main thing here is to find the right length. Since hub dynamos usually have slightly larger flanges than normal hubs, you will probably need shorter spokes, in which case a spoke calculator will come in handy. Our wheel building guide has further instructions on how to determine the dimensions you need to make this calculation, and also outlines the differences between various types of spokes.

Lacing and truing with a hub dynamo

If you need general advice on lacing and truing wheels, feel free to check out our tips for wheel building. It will give you theory and practical guidance in the form of video tutorials and overview texts. A special feature of the hub dynamo is that the generator already contains some resistance without a load applied by a light. When you turn the wheel in the truing stand, you will notice this as a slight stutter or jerk on some models. This should not worry you, as it is virtually imperceptible while driving. A stable truing stand helps to ensure that truing is kept precise and easy. With a hub dynamo, pay attention to the correct running direction. This is self-explanatory with dynamos for disc brakes, but the rule of thumb helps with rim brakes: connect the power on the right.

A stable truing stand makes it easier to spoke and true your new wheel.
A stable truing stand makes it easier to spoke and true your new wheel.

A stable truing stand makes it easier to spoke and true your new wheel. © bc GmbH

The right lighting

Now that you have a new wheel with a hub dynamo, you will probably want to install lighting on your bike. You should make sure that the front and rear lights match the dynamo as well as each other. In contrast to lights for classic side-rotor dynamos, those for hub dynamos usually have a switch. Otherwise, they would be permanently lit since the dynamo cannot be switched off. To make full use of the dynamo’s potential, the power consumption of the light should match. For a three-watt dynamo, it is also worth buying a three-watt light. These days, LED has become the standard light source. If you want to install a rear light and front light from different manufacturers, you should check whether the rear light has an integrated capacitor for the parking light. This is not the case with some manufacturers, as the rear light then relies on the capacitor in the front light. When retrofitting a lighting system, think about the mounts and the wiring as well. Does your bike have cable guides on the fork and frame? Are there places where you can mount lights? To help you choose the right bicycle lighting, we have a light comparison test with current models from various manufacturers as well as detailed advice.

A hub dynamo ensures that you can never forget your light on your bike. And: you’ll always have power with you on the road, which you can use to charge your smartphone or GPS devices.
A hub dynamo ensures that you can never forget your light on your bike. And: you’ll always have power with you on the road, which you can use to charge your smartphone or GPS devices.

A hub dynamo ensures that you can never forget your light on your bike. And: you’ll always have power with you on the road, which you can use to charge your smartphone or GPS devices. © bc GmbH

Power supply for other devices via USB

On long tours and trips, a hub dynamo is an ideal power supply for your smartphone, bike computer and other devices. For this, you need an additional device that regulates voltage and current and channels them via a USB charging socket. In most cases, a buffer battery provides constant current for charging, even when you’re at rest. The brand busch+müller currently has two chargers in its range, the E-Werk and the USB-Werk, which are attached to the frame. In addition, there are front lights that combine light and USB charging function in one device. Cinq offers the Plug5 system with or without a buffer battery. It sits inconspicuously in the steerer tube instead of the headset cap on the stem. Hidden installation in the steerer tube is also offered by the AppCon system from NC-17. However, the units differ in terms of power output. The products’ descriptions include information about the speed at which they deliver power and how much. To be able to charge devices that are not mounted on the handlebars, we recommend a small padded bag on the top tube or a handlebar bag.