Dynamos for the bicycle lights

It’s a nice feeling to have permanently installed lighting on the bike, which works with the flip of a lever, just like you know it from cars. Welcome to the world of the bicycle dynamo (sometimes called alternator).

People from baby boomers remember clunky whining contraptions that ran on the side of the tire. The light flickered and was meager at low speeds. The bulbs burned out if you went too fast and you were slowed down by the dynamo when you activated it. And one day the things suddenly stopped working.

Modern dynamos are far superior mechanically and electrically to these old devices. They produce the same amperage, but through electronic output control, significant advances in LED technology and lamp optics, they produce much better light at all speeds – even when you stop. Even competitive endurance cyclists have modern dynamos and LED lighting and ride them for many hundreds of miles in competitions that last for days and nights on end.

Table of Contents

Advantages and disadvantages


Maintenance free and always ready! You want to extend your evening ride? You’re traveling and can’t recharge batteries or don’t want to have to worry about it? You don’t want to have to worry about new batteries or constantly forgetting to pack your clampable light? No problem!

Theft-proof! Dynamos and their lighting systems are permanently mounted on the bike while clamp lights can be taken by any passerby. If necessary, theft-proof fasteners can be used for additional security. You don’t have to disassemble the light and take it with you when you park your bike.

Environmentally friendly! No battery waste, no toxic materials.

Higher electrical reliability! The electrical connections on the dynamo are usually permanent. Battery lights often suffer problems with poor connections. Particularly affects battery contacts or external wiring, which are frequently unplugged and plugged in.

Higher mechanical reliability! Many battery lights are comparatively windy designs, often held together only by small plastic tabs and clamped to the handlebars so they can be quickly pushed out of position by hands or knees. Often these lights misalign just by passing through a pothole. Dynamo lights are typically more stable.

Higher system reliability! The most common reason for battery lighting failure is a lack of battery capacity – either disposable batteries that are depleted, or rechargeable batteries that are not sufficiently charged (anymore). Rechargeable batteries lose capacity over time and often fail unexpectedly for the rider. Dynamos just work all the time.


More difficult to find! Meanwhile, dynamos and associated lights are less common than battery lights. Due to changes in the 2016 StVO, battery lights are also allowed on bicycles under certain conditions. Therefore, one must resort to online ordering more often

More difficult to mount!. Side-rotor dynamos and roller dynamos (see below) must be properly aligned with the tire to minimize drag. You have to lace a hub dynamo into a wheel. Lamps must be bolted down and wiring should be done properly. Some units have difficulty with carbon forks. In general you can say that you should have some mechanic skills and some electrician skills. However, once a system is properly installed, there are few problems.

Resistance! This is a minor problem that is often overrated. Chris Juden, technical editor of the Cyclists Touring Club of Britain Has noted that modern dynamos produce a resistance equivalent to a rise of about 3.8 meters per kilometer (20 feet per mile). Really good models are the equivalent of 1.15 meters per kilometer (six feet per mile). However, this may still seem important to some. An unintentional test by article author Frank Krygowski showed that an unintentionally turned on dynamo had reduced his average speed from 32 mph to 30 mph.

Smaller maximum power! Typical dynamos have an output power of three watts and some models perform even six watts. Battery lights can consume up to 20 watts. However, modern LEDs and carefully crafted optics are perfectly adequate for road use at a power of three watts. However, a mountain biker will be better off with battery lights.

Noise! Side-wheel dynamos may emit an audible whine where they touch the tire. Most other types are more or less silent.

Danger of slipping! Roller dynamos mounted on the bottom bracket shell can slip when mud covers the tire surface. Side-wheel dynamos can slip in heavy rain or snow unless special drive wheels are fitted. Hub dynamos are immune to such problems.

Difficult to replace from bike to bike! In general, one dynamo set is needed for each bike you want to ride at night – at least for each front wheel.

Burning out bulbs, no light when stopped! This is a problem from the (literal) dark past. Modern lamps have better electrical control, their LEDs last virtually forever and built-in capacitors keep the light on for quite some time before it goes out when stopped. If you don’t want to buy a new dynamo, you can at least help yourself with a new lamp. Many new lights will work fine with the low output power of a Sturmey-Archer Dynohub.

Expensive! A modern dynamo typically costs about twice as much as a battery-powered system with comparable light output.

Dynamo or battery?

Dynamos are preferred for bicyclists who cannot predict in advance how long a ride will take in the dark, who are taking a bicycle trip, or who are otherwise traveling and taking a bicycle with them – for example, taking a train trip and using a bicycle at their destination. Cyclists who use the bike for sports can be better equipped with battery lights. However, it has been found that participants in Paris Brest Paris (a 1200km randonnee) who used dynamo lighting were significantly more satisfied with their lighting than battery light users. Mountain bikers will probably almost always be better off with battery lights.

How it works

A bicycle dynamo has a stationary wire coil that is connected to the front light and usually also to the rear light. Permanent magnets rotate inside the coil either through a roller that contacts the tire or the magnets are connected to the rotating parts of a hub. When a magnetic field moves near an electrical conductor (for example, a wire coil), electrical voltage is built up in the wire (equivalent to pressure in a pipe). When the wire is connected to a carefully selected electrical load (for example a light bulb), current (equivalent to the flow in a pipe) is generated and light is produced (very simplified illustration).

The faster the rotation of the magnets, the more power is produced. In the past, this often leads to bulbs burning out when riding very fast. Nowadays, the problem has been solved by advances in electrical control technology in the systems.

Dynamo types

There are three known types of dynamos that use rotating magnets to generate electricity. Each of these types has its own advantages and disadvantages.

Side-wheel dynamo

This type was the most common for many years. The shape of the dynamo is roughly reminiscent of a bottle and the drive wheel is roughly the shape of a crown cork. Therefore this type is also called "Bottle Generator" (bottle dynamo). the drive wheel leans against the side wall of the tire. Some tires have an extra grooved "dynamo track". The wheel thus drives the drive train of the dynamo. Inside, this strand drives the magnets. In the picture on the left you can see a modern bush& Muller side rotor dynamo.

  • The cheapest version
  • You can often find used ones to give away
  • They are small and light
  • They can be mounted on both the front and rear wheel
  • Switching off requires only swinging the drive wheel away from the wheel of the bicycle
  • In the switched off condition (thus contactless) no resistance
  • During use (i.e. in contact with the tire) they have the highest resistance of all types.
  • They have a tendency to slip in heavy rain or snow.
  • They produce noise.
  • In the case of very light tires, there may be increased tire wear.
  • To minimize resistance and wear, the dynamo and the mounting point must be carefully aligned to the wheel.
  • If the wheel has a figure eight, the dynamo will slip through
  • Clamping devices are attached to fork or frame and are not advisable for carbon.
  • Dynamo and mounting clamps are visible and affect the appearance of the bike.

Roller or bottom bracket dynamos

This little used unit was usually mounted between the cranks and rear wheel underneath the bike. The roller is in contact with the center of the tread and not the sidewalls of the tire. This type is no longer manufactured and you can occasionally find roller dynamos NOS or little used.

  • Small and very inconspicuous
  • A slightly more protected position, which can be valuable especially on folding bikes.
  • In switched off condition no resistance
  • Few problems with tire wear, because only the tread of the tire is used.
  • The large pulley produces slightly less resistance than the pulleys of side-wheel dynamos
  • Quieter than side-rotor dynamos
  • Higher tendency to slip in mud or snow conditions
  • Sticky asphalt collects on the roller and can cause vibrations
  • Roller and bearing wear are accelerated by dirt.
  • Difficult to activate and deactivate without getting off the bike
  • Mounting can be difficult when space around the bottom bracket shell is limited.
  • Cannot be combined with bike stands mounted on the bottom bracket shell.

Hub dynamos

This type replaces a hub on the front or (rather rarely) on the rear wheel. You build up a wheel with them as hub, if you don’t buy a complete wheel with hub dynamo. Most hub dynamos have no external moving parts. there are few models that have an external clutch that can be used to further reduce resistance. Hub dynamos are often considered the best dynamos for bicycles and have rapidly gained market share in recent years. Especially popular on transport bikes from European manufacturers, as it avoids having to (re)assemble the wheel.

The first hub dynamo was the Dynohub from Sturmey-Archer, which was produced from 1936 to 1984. Sturmey-Archer (now no longer British but Taiwanese) launched a new model in 2010. In the article Dynohubs you can find more information about these models.

The fanciest and most expensive hub dynamos are made by the German manufacturer Busch& Muller distributed. Their special feature is the protection against condensation and moisture inside the dynamo. The models are manufactured for a wide variety of installation widths and tire sizes.

  • They are the most efficient and reliable bicycle dynamos that have the least resistance when you activate them.
  • No slippage possible
  • Very inconspicuous and therefore low probability of theft.
  • Easiest to move from bike to bike if wheel sizes remain the same.
  • The most expensive type, especially as a spare part.
  • You have to build a wheel around the dynamo, which most cyclists only leave to a bike repair shop.
  • Minimal resistance even if it is turned off – but this is almost negligible for most models.
  • Unlike other types, small wheels require special models because the speed of rotation increases significantly with small wheels. (The speed of the tread is not affected by the wheel size, so this is not an issue with sideways or roller dynamos.)
  • Some hub dynamos produce a very slight vibration on the handlebars at certain speeds.
  • Lights may flicker at very slow walking speeds. Possibly. this is even an advantage, because more attention is produced than with constant light.

Dynamo mounting and wiring

As mentioned above, it takes more mechanic skills to mount any dynmao than it does to clamp on a battery light. A little knowledge of electricity is also quite helpful. Here are a few tips and considerations.

Mounting points for sidestage and roller dynamos must be stable. Loctite or other threadlockers are useful. Side-rotor dynamos should be mounted in front of the fork blade or seatstay, and never behind it, to eliminate the risk of the dynamo getting caught in the spokes.

Side-rotating dynamos come in different varieties for mounting on the right or left side. If the correct variant has, the dynamo swings properly against the side surface of the tire presses and unnecessary resistance is avoided.

All dynamos need two wires. the electric current flows to the light and a wire is needed back to close the circuit. Some old sidestage dynamos used the metal of the bike frame to close the circuit and a pointed screw was driven through the paint to the bare metal of the frame. this was a regular problem. It is much better and easier to use two wires. one is the conductive wire and the other is the "ground". Hub dynamos are supplied with two conductors. Conducting bifurcations are just right for this purpose. A carbon fork or carbon frame does not conduct electricity. Here two wires are essential as conductors.

Never swap the two wires. Some people take bundles of two and connect the power conductor to ground. this looks unsuspicious at first, but you will not be able to generate light. You should follow the two wires closely and pay close attention to which wire is connected to what.

Keep control of the wires. Smooth the wires before you mount them – there should be no kinks or bends – and make them run in a straight line. Possibly. the back of the fork blade is a good clue. Following the brake or shift lever also works very well. By means of cable ties you can fix the wires to the frame or to the traction sheaths. However, leave them loose enough for the fork to move freely. The following illustration shows how to wire a Shimanodynamo.

Hub dynamos need a switch. As the magnets always rotate with the hub, it is normal that a hub dynamo needs an on/off switch. In the case of a headlamp that is not switched, you can either retrofit a switch in the circuit or always ride around with the lights on (daytime running lights). side and roller dynamos do not require a switch.

Side rotor dynamos need proper alignment. Roller dynamos must be accurately aligned parallel to the wheel. Usually this is guaranteed by the mounting plate soldered firmly to the fork on the frame. The rotation axis of the dynamo must overlap with the rotation axis of the wheel. this requires meticulous alignment. In addition, the drive pulley of the side-wheel dynamo should not run over parts of the sidewall with elevations such as embossed brand names or the like. Some tires have a special dynamo track on their sidewall. These are smooth except for a slightly roughened surface. A few side-rotor dynamos have rubber rollers that can also run on the brake flank of the rim. These are very quiet and have little tendency to slip.

Additional connections. A dnymao can also be used to charge a lamp for overnight camping. Or you charge a GPS device or your cell phone. See also Harriet Fell’s article RideWithGPS (English)

What about carbon? The popularity of plastic bicycles in particular has made it more difficult to fit sidestage dynamos. Clamps on fork or frame are rarely recommended. One needs specially made clamps, if that is actually possible. Hub dynamos have no problem with carbon parts. In general, you can say that who can afford a carbon frame, also has money for a hub dynamo!

Think about the position of the headlamp. Headlamps on handlebars are quite popular, but there are better positions on the bike. If you mount the headlamp between 65 and 75 cm above the ground on the crown of the fork or above the front rack, the lamp can illuminate the asphalt similar to a car light. Potholes can be seen better, stones and bumps in the road are clearly illuminated and glare in snow and rain is minimized. Randomly ripping off the wire is almost impossible. There’s no interference with handlebar bags or a rain cover, and you have more room for your bike computer, GPS, a compass and your Mickey Mouse bell! Some lights have a better light pattern than others. See also more in the article The right choice of LED lamp.

Light and optics

Bicycle lighting has come a long way while illuminants have steadily evolved. In the 1970s, dynamo and battery lights with simple incandescent bulbs were never really bright and also got dimmer over time. These lights could be considered marginal at most, and they really only served to make sure you were seen and could ride in well-lit city streets.

Halogen bulbs appeared in the late 1970s. These were significantly brighter than comparable incandescent bulbs and didn’t get dimmer over time. Simultaneously, the reflectors and lenses of headlamps were designed to cast focused light onto the road in front of the bicycle – similar to motorized vehicles. Since light was not wasted by lighting the street trees above, one could now recognize potholes and objects on the roadway. Bicyclists now became more visible to motorized people.

In the 1980s came the first LED tail lights. These red turn signals were even more energy efficient than the modern halogen bulbs, so small batteries lasted for a whole season. Although not allowed in Germany, this brought attention to the fact that there was a cyclist on the road. Bright LEDs were only available in red at that time.

In the 2000s, thanks to an invention worthy of a noble prize, it was possible to produce powerfully luminous white LEDs. Since then, the efficiency of white LEDs has skyrocketed year by year, producing more and more light for the same amount of power. Battery lights can now produce light bright enough to rival a car’s high beams. Even dynamo light can be proverbial dazzling.

In the U.S., bicycle lights are virtually unregulated. There are a few vague minimum standards ("visible up to 150 m away"). So it is technically legal to use a light that blinds oncoming motorists. This is even worse for oncoming cyclists on narrow bike paths with oncoming traffic.

In contrast, in Germany, the need for proper optics was followed early on. Lights on vehicles in Germany are subject to the German Road Traffic Licensing Regulations (StVZO), which prescribe minimum light levels at various positions within the light beam and maximum brightness above the shield to prevent glare for oncoming vehicles. The best lights for road use are those that comply with StVZO regulations, whether they are battery or dynamo lights.

The benefits are possibly greatest for dynamo lights. The efficiency of modern white LEDs and the efficiency that must be met by the StVZO allow a luxurious road illumination, if you use a modern dynamo. Expected further advancements in LED technology will certainly improve this situation even more.

Test the lighting!

One last tip: Some overly presumptuous cyclists ride at night with tiny lights or even without them. Some overly cautious riders are overly afraid to ride at night and start with blinding lights and distracting strobe lights. How to decide what is really reasonable?

The best way is probably to rely on the help of friends. Go for the usual night rides – whether off-road or in town – and have a friend ride your bike so you can watch the lights yourself. First look at it as a passerby on foot and if possible also again from the perspective of a car driver. Observe the light from several perspectives if possible. After that you can probably decide if the light is bright enough or too bright and if the reflectors in combination make you visible enough.

Now do this favor for your friend too and he can test his lights. It will pay off!

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