Bicycle Dynamo Hubs & Lights (Commuter’s Guide + Recommendations)

Ever forget to charge your lights, or trying to eke a few more minutes out of a super-low beam?

Or remember to charge them…only to forget to put them back on before heading out the door?

Bicycle dynamo lights take charging out of the equation. They also let you use headlight models with specially design that help you see more and reduce glare to others.

If you’re in a hurry for specific bike suggestions, then skip over to this run-down of my favorite dynamo-equipped bikes for commuters.

Otherwise, read on to learn more about how these nifty systems work and why you might (or might not) want one.

How do dynamo hubs work?

Remember that electromagnetism lecture way back in physics class? Well, it’s about to come in handy.

In short, when the right sort of coils rotate around each other, they create an electric current (as in Faraday’s law). Bicycle wheels are practically always moving, so sticking the coils inside a hub is a simple way to keep the current coming. And with that flow of electricity, you can simply connect a pair of wires to power a headlight, taillight, and even USB charger forever.

In practice, it looks something like this:


You might be thinking:

“OK, but what happens when I stop? I don’t want to get run over when my lights go dark.”

That makes two of us!

Fortunately, the engineers are a few steps ahead on that point. Nearly every decent dynamo hub on the market today includes something called a capacitor, which works a bit like a rechargeable battery.

If you’re riding more than a couple miles an hour, the hub will generate more electricity than the lights require. The excess overflows into the capacitor, which stores it for later use. It thus keeps the lights on when stopped for up to a couple minutes.

To be clear, the headlight in particular is dimmer when at a standstill, lest it drain that reserve before the stoplight changes. Taillights stay closer to full brightness since they use so much less power in the first place.

You do have to ride for perhaps 15-60 seconds (depending on speed) to “fill” the capacitor, but it’s only a concern if your ride begins at a dead stop on the street. And if so, then buy a cheap clip-on light as a supplement, which never hurts to have.

It’s also worth noting that a flashing light is impossible (to my knowledge) with dynamo-powered lights. But a flashing beam is useful around traffic, especially in the daytime. If that’s a situation you typically ride in, then it’s worth supplementing your dynamo lighting with a cheap rechargeable light with a non-strobe flashing pattern.

Why would I want dynamo lighting?

Far and away the biggest benefit of dynamo lighting is that it literally never requires charging. For commuters, it’s nice to avoid the headache of remembering to charge (or dealing with the consequences of forgetting to do so). For touring cyclists, it’s essential for all-day, all-night lighting without carrying stacks of spare lights or batteries.

Another oft-neglected benefit of dynamo lighting is that most headlight designs are simply better.

How so?

First, consider that clip-on lights can be mounted literally anywhere. That calls for a round beam that projects identically whether right side-up, upside-down, or anywhere in between. That entails a circular beam that’s very bright in the center…but fades to nothing toward its perimeter.

But with dynamo headlights, they’re always fixed (by a screw-on mount) into one single position. The manufacturer knows and requires that they’ll always be in one orientation, so they can optimize the beam to use the squared-off pattern of car headlights. That means more even illumination for you (no bright center/dim edges) and far less glare for others.

(There are actually a few clip-on lights with squared-off beams, like the inexpensive PDW Pathfinder I own, and a few nicer but rarer B&M models that I’d quite like. You’re just not likely to find them in a local shop.)

So why doesn’t every bike have dynamo lights?

The upfront issue is cost. Most North American manufacturers typically leave accessories up to the owner, and that’s all the more true for expensive “accessories” like dynamo lighting. (I consider it an essential, not a necessity, but our sport-driven bicycle market says otherwise!)

Likewise, retrofitting your bike will add significant cost: from a few hundred dollars on the low end to (at least) many hundreds for top-of-the-line everything. The lights themselves can be had for not much more than than good clip-on lights, if you’re on a budget. The real expense is the front wheel: you’ll need to replace the front wheel or have your current one rebuilt around a dynamo hub. That’s a prudent and minor expense on a bike you’ll ride daily for many years, but it’s not cost-effective otherwise.

Money aside, there are some small disadvantages in weight and efficiency.

Even the extremely light Shutter Precision S-8 hub (350g) still adds a couple hundred grams–roughly half a pound–over an inexpensive standard hub. That’s irrelevant for practical and casual riding, but it’s enough for many racing cyclists to care about.

There’s also a slight drag in the front hub when the light is on and the coils are active. That’s just a byproduct of converting motion into electricity, since it’s physically impossible to do that with 100% efficiency. This is very low on good, modern hubs–especially compared to the horrendously inefficient sidewall dynamos of yesteryear. Just like weight, the hub’s internal drag is trivial for practical cycling but a minor drawback for performance riding.

Which hub and light brands should I look for?

Virtually any modern dynamo hub from any reputable retailer will perform well. The market just isn’t that big, so you’ll likely choose from:

  • Kasai
  • KT
  • Schmidt/SON
  • Shimano
  • Shutter Precision (rebranded as BioLogic Joule on some bikes from Tern and perhaps Dahon)

You will not go wrong with a recent model from any of them. Your decision may come down to axle and disc brake compatibility.

The general consensus seems to be that SON has the lowest drag of all, but Shutter Precision gets remarkably close for remarkably less money. And as a Shutter Precision owner twice over, I’ve never even contemplated buying another. The only exception would be if you need maximum power for USB charging at lower speeds–perhaps 10 mph or less–where the SON is reportedly more efficient. Then again, that need doesn’t arise unless you’re touring. It’s simply overkill for commuting, transportation, or leisure cycling.

Importantly, all the above are 6V3W (“six-volt, three-watt”) hubs, unless you’re dealing with outdated models. That’s critical because it ensures compatibility with as many lights as possible.

Speaking of lights, most of your thought and money should go toward the headlight. It’s much harder to design a perfect beam for illuminating your path than it is to design a visible taillight. Consequently, headlights are more expensive but also make a bigger difference for the rider.

Busch & Mueller is by far the most common light brand for aftermarket dynamo upgrades. I’ve owned and adored both the B&M IQ-X (likely the brightest on the market at 100 lux) and IQ-XS (smaller but still plenty bright at 70 lux), both of which have wide, even beams with ample light for totally dark conditions.

Entry- and mid-level B&M lights are also common on stock bicycles. They usually give 30-40 lux and have narrower beams. That’s fine for urban riding, since streetlights and buildings cast a lot of ambient light. But for unlighted paths or trails, it’s worth upgrading to one of the above.

As with hubs, Schmidt/SON also has a well-regarded but expensive headlight called the Edelux (which apparently uses a B&M mirror to shape the beam). At 90 lux, it’s a bit less bright than the IQ-X, but not consequentially so. And the Edelux’s smaller body may be easier to mount in certain ways.

For taillights, the Busch & Mueller Toplight Line Plus is impossible to beat. The “Brake Tec” edition even has a pulsating brake light for extra visibility! And at only $60, give or take, there’s little sense in trying to save a few more bucks.

Spanninga and Herrmans are also popular and reputable brands with good headlight and taillight options. Spanninga taillight are common on North American bikes, but otherwise, they seem far more prevalent in Europe.

That’s not the entire market, by any means, but I’ve yet to find a scenario that one of the above don’t excel in. As a rule, do your homework on no-name or proprietary lighting, which may lack important features like a squared-off beam. That’s not always the case, but well worth verifying.

Quick picks: stock city bikes with dynamo lights

In Europe, there are too many options even to list. They’re not only common, but nearly universal on city, commuter, and even touring bikes.

But in North America, the list is regrettably short. A few hundred dollars for a dynamo upgrade is worth it for daily use on a bike you’ll own long-term.

Still, it’s nice to save money and hassles by buying something fully equipped off the rack. And if that’s what you’re after, then check out this guide to some good value bikes with all that and more.