Designing the Rene Herse Taillight

Designing the Rene Herse Taillight

If you’ve been to the Philly Bike Expo last weekend (or looked at the photo feeds), you’ve seen many custom bikes with our Rene Herse taillights. (Above is Brian Chapman’s.) The taillight has been one of our more popular products.

As with so many projects, it all started when I needed a part for my bike and couldn’t find what I wanted: An elegant taillight mounted directly to the bike without clamps and brackets. Generator-powered – the last thing I want during a long ride is run out of batteries (or worry about it). And with the latest technology and safety: a bright and long-lasting LED that doesn’t burn out, and a standlight, too.

My taillight had to incorporate a reflector. Not only is it safer – in the unlikely event that the taillight stops working – but it’s actually required by law in many countries. My friend Hahn suggested using the reflector as the taillight lens. Not only does this eliminate the need for a clumsy separate reflector, it also gives a diffuse light that is easier on the eyes for cyclists drafting closely behind my bike. From a distance, it’s just as visible: The light output in lumens is the same, just spread over a larger area.

There was no taillight that met these requirements. So I decided to make my own.

Where to mount the taillight? That was easy, since René Herse figured it out long ago: I don’t carry huge saddlebags, so the rear of the seat tube is the perfect place for the taillight. Nestled between the seatstays, the light is well-protected, yet easy to see from behind. Routing the wire is easy, too, since it can go through the frame.

Finding a good circuit for the electronics was no problem, either: The B&M Seculite Plus has a bright LED and a standlight circuit. Its LED mounts in the center of the round capacitor that powers the standlight. The Seculite Plus represents the state of the art in taillights. It has proven ultra-reliable. And it has the right shape for my taillight.

Finding a good reflector was more difficult. It turns out that many reflectors don’t reflect well at all. I wanted mine to reflect at least as well as a car’s reflector.

Most reflectors are made in Asia these days, so I asked our engineer in Taiwan to round up every reflector he could get his hands on. At night, I put each batch on the rear bumper of a car, shone a light at them, and compared. It took a while, but we finally found a reflector that worked extremely well – and also was round and the right diameter.

I didn’t take photos during that initial test, so I recreated it using my bike with its taillight. The reflector works so well that one might think the LED inside is illuminated, but it’s just the reflector in the beam of a flashlight.

Then it came to designing the shape of the taillight. There are many beautiful taillights, but none have a flat lens. Reflectors are flat, so I needed something different: I quickly realized that all the shapes designed for domed lenses would not work.

Looking for inspiration, I finally came upon this JOS reflector. It’s prized by collectors, for not only is it ultra-rare, but it’s also very beautiful. I realized that the wide ‘ring’ is key to making the shape work with the flat surface of the reflector.

With the JOS reflector as a starting point, I drew a variety of shapes. It would have been easy to draw a simple ball, cut in half, but that isn’t really aesthetically pleasing.

The shape of the taillight was constrained by several factors. In addition to the flat rear surface, I needed enough space inside for the electronics, especially the big capacitor that powers the standlight. I finally came up with a shape that transitioned nicely from the lens to the taillight mount on the seat tube.

For a moment, I thought about the German requirement that taillights must be visible from all sides. Shouldn’t my taillight at least be visible from the sides for safety? Actually, your bike is moving forward – to avoid getting hit from the side, you need to be visible from a 3/4 front view. When you are right in front of the car, you’re no longer in danger: By the time the car reaches the spot where you are, you will be gone. It’s the same with wheel reflectors: They look very impressive when they light up in a car’s headlight beam, but they don’t do anything to make the rider safer.

So why do German taillights need to be seen from all sides? Andreas Oehler from SON explained: “It’s so that riders can look back and see whether their taillights still work.” Now I understand! That was useful in the days of filament bulbs, which burned out frequently. Not only do LEDs rarely fail, but it’s a non-issue on bikes with polished fenders: The reflection of the taillight is visible from the saddle even if the lens itself is not. You can see the taillight’s reflection in the top photo of Brian Chapman’s bike. I was glad to have resolved this issue!

The next step was to make the actual light housing. Machinists will laugh: I machined it free-hand, just shaving away material, ‘etch-a-sketch’ style, until I had the shape I wanted.

Now that I had all the parts, I sent them to our engineer, so he could make the production drawings. A few days later, the phone rang: “What is that shape? I’ve measured it, but I can’t find a curve that describes it.” I explained that there wasn’t a curve since the light’s body had been drawn and machined free-hand.

At that point, we both realized why the old lights are so graceful: They were drawn by hand, and the tooling was made from wooden masters that were also carved by hand. These days, parts are CNC-machined, so they tend to be composed of simple curves and straight lines.

Of course, we needed to CNC-machine our taillight housing, so it was up to our engineer to translate my prototype into a series of curves. It’s not impossible to describe a hand-drawn shape as a series of mathematical curves – it’s just a lot of work.

There was more to do. We also needed a braze-on. Since the seat tube is inclined, the braze-on has to be mitered just right. Plus, we wanted the braze-on to extend into the seat tube, so it acts as a stop for the seatpost and protects the wire. Otherwise, inserting the seatpost too far would damage the wire…

We designed a two-piece braze-on (this is the second version) that can easily be filed (at the square end) to move the light closer to the seat tube, giving the builder options for customizing the fit. There are also some parts inside the taillight to hold the circuit board securely and ground it against the light’s housing, so the frame can be used as a return for the current.

Then it came to producing the taillight. The housing is CNC-machined from aluminum, then polished. The internal parts are laser-cut from stainless steel. The braze-on is machined from steel. (This photo shows the first generation braze-on.) The wire is a special automotive wire, which is insulated with a cross-linked polymer that is extremely abrasion resistant: It won’t chafe through where the wire enters and exits the frame. We persuaded Busch & Müller in Germany to sell us separate circuit boards from their taillights.

The hardest part turned out to be the reflector. The lens was glued into the plastic housing. By pure chance, our first sample (for the prototype) had come apart easily, but when we bought a large quantity, we realized that most were glued in permanently. We had to saw off the housing and then break the reflectors loose. About half of the reflectors cracked during this operation. We talked to the sales representative for the reflector company about getting just the lenses, but that was not easy. It’s not a part the company usually sells, and we didn’t need a million of them, either. Finally, our sales guy took pity on us and simply picked up a box of reflectors when he visited the factory. We treated him to a nice dinner as thanks (and paid for the reflectors, of course).

All those parts are assembled right here in Seattle in small batches by our friend Alistair. The taillights have been very popular, and sometimes, he can’t keep up with demand. Recently, we’ve been out of stock, but Alistair has just completed another batch.

All this is a lot of effort for a ‘simple’ taillight, but we think it’s worth it – because there are no alternatives that work as well and look as nice.

We sometimes get questions for a fender-mounted taillight. It would make it easier to retrofit a bike with the taillight, and it can be an option for small frames where the rear wheel obscures the seat tube. We don’t offer a fender-mounted taillight yet, because we haven’t found a pleasant shape that is large enough to house the electronics. Simply sticking our taillight onto a fender wouldn’t look nice – the shape has to flow with the fender. Making an ugly taillight makes no sense – I’d rather mount a modern plastic light to my fender!


So for now, our taillight mounts on the seat tube. When you order a custom bike, it’s a great choice, or you can retrofit an old steel frame, as BQ team rider Steve Frey did with his Frek (a 1980s Trek converted into a randonneur bike, above).

Click here for more information on our lights.

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Comments (23)

  • Gerhard Kohl

    One can use your taillight as well to attach it to the chain stay, as my builder did it for my Rinko randonneur. My frame is not very large and I’m using for long Brevets a saddle bag.

    November 5, 2019 at 5:38 am
    • Jan Heine

      We’ve thought about this, too. Alex Singer mounted their taillights there, and, way back, BQ team rider Mark equipped his ‘Six Hands’ with a DIY light that’s mounted under the chainstay. My only concern is that the light is exposed there, and the aluminum housing can break off the (aluminum) threads if the bike falls over and the taillight hits the ground first. Maybe mounting the light close to the bike’s center, so that the saddle would touch first, is the solution…

      November 5, 2019 at 11:01 am
  • jamiroblog

    Absolutely wonderful work. Plus: Great illustration that simple solution require a lot of work (and to add somethinK).

    Looking forward to seeing your fender tail light, because many of us are using saddle bags, especially on longer tours.

    November 5, 2019 at 5:38 am
  • Nils Anders

    Dear Jan,
    the most gorgeous fendermounted taillight is the Soubitez Catalux No. 6.
    A shape like that should be big enough to fit all the electronic parts.

    Yours Nils

    November 5, 2019 at 6:20 am
  • Sean

    I love the light. However, as I don’t run a generator system, I would be so grateful if you could create a battery-powered light of the same design. Even better would be the ability of such a light to attach to a saddle bag.

    November 5, 2019 at 7:12 am
    • Jan Heine

      Attaching a light to a bag is convenient, since most bags have loops. However, it’s very difficult to design a good light that clips to a bag, because the angle of the light depends on your saddle position, the bike’s seat angle and how much you carry in the bag. To be effective, the light (and especially the reflector) has to be pointing straight at the traffic that is approaching from behind. If it’s at an angle, it becomes less bright (as seen from behind), or even invisible (as happens with most lights clipped to backpacks or clothing).

      A possible solution is to use several LEDs and reflectors, mounted in a semi-circle, so that one is always pointing in the right direction. To avoid wasting batteries on LEDs that aren’t visible, you could incorporate an angle finder that automatically switches off the LEDs that aren’t vertical. It gets very complicated (and expensive).

      November 5, 2019 at 8:05 am
  • Allen Potter

    I just switched out the battery operated light on my Boulder Brevet. After a while, you just get sick of worrying about batteries (I remembered to turn mine off about 95% of the time, which is not nearly good enough). I loved the shape of that light, but now that I have one of your lights connected to my hub generator, I am in love with it. Mounted right into the existing braze-on. No more worries about batteries, and the light is more powerful. The standlight function actually lasts longer than the front Edelux light. I hesitated to make this upgrade because it wasn’t cheap. Now that I have it, I’m really glad. Sweet product!

    November 5, 2019 at 7:20 am
  • Philip K. Lussier

    Elegant bicycle components all have their backstories. It’s nice when we can learn some of them.

    November 5, 2019 at 7:33 am
  • Sean H

    Regarding the fender mounted light: You’ve fabricated most everything else so far. Why not take it one step further and design (or have designed) a PCB (printed circuit board) to hold the electronics in a shape to match your desired housing profile? It would truly be in the spirit of Rene Herse!

    November 5, 2019 at 8:15 am
    • Jan Heine

      Making a circuit board isn’t hard, but making one that survives the shaking of 10,000s of miles of gravel roads at race speeds is a lot harder! Others have more experience with this, so we’re happy to work with B&M on this. 😉

      November 5, 2019 at 8:33 am
  • Rod Bruckdorfer

    I am amazed at the number of dynamo driven tail light. As an example bush&muller has 14 and I am to believe Rene Herse is better.

    November 5, 2019 at 9:49 am
    • Jan Heine

      Since Germany requires generator-powered taillights, there is a huge market for them… The B&M lights are great. The Rene Herse is a little brighter than the Seculite that uses the same internals, since the aluminum housing doesn’t absorb as much light as the black plastic one, but it’s not a lot. The main reason to use the Rene Herse is that we like the way it looks and the way it mounts on the bike.

      November 5, 2019 at 11:53 am
    • Matthew J

      Thus the beauty of market variety.

      As Jan says, there is not one Busch Muller designed to mount on the back of the down tube.

      Not so much a competition for being the better light, but rather filling a niche B&M does not currently fill.

      November 7, 2019 at 5:43 am
  • RickH

    Great story in how much effort goes into a light that is otherwise taken for granted. Some people may think you pull a design out of the air, give it to a factory who will deliver the product to you next week. Not so, especially if you want it perfectly to your design.
    I like your patience and tenacity to stick with your design. Well Done.

    November 5, 2019 at 12:44 pm
  • John Edward McClain

    Jan, I’m a machinist, and I wouldn’t laugh at all. I don’t do “cnc” I do the old school, and think that is a beautiful piece of work, well designed, and I’ve dealt with the same issues on motorcycles, as well.
    I’ve got a rusted old Packard or something the like, which has a beautiful contour, would just have to be down-sized, to go on a fender. I believe I will get one of those lights.
    Very nicely done.
    Semper Fi,
    John McClain

    November 5, 2019 at 2:58 pm
  • billm

    I never give any thought to my little RH taillight. It just works.
    That is meant as high praise btw. If only more technology were like that.

    November 5, 2019 at 3:52 pm
  • willemjongman

    This is really beautiful. However, it does not seem to meet the K920 specification to make it legal in e.g. Germany (I am sure it will be more than good enough, however).
    As for fender lights, Schmidt make a very neat and tiny one, of course, even if it does not have an inbuilt reflector. For my town bike (a 1988 Koga Miyata) I did something different that looks authentic though perhaps not that nice. I used a modern B&M taillight for an incandescent bulb, and replaced the bulb with a reflectalite led bulb. This is quite a bit brighter, but uses the existing approved reflector. The only downside is that it does not have a standlight function.

    November 6, 2019 at 1:39 am
    • Jan Heine

      The cost of getting the taillight approved in Germany is too high for us to make it worth the effort. However, when mounted on a bike with fenders, it meets all the requirements regarding light intensity, reflectivity and visibility from the rider’s view (to check that it’s working).

      For your taillight, I recommend our LED Retrofit Taillight Bulb. It screws right into the socket for an old incandescent bulb, but it’s brighter and lasts forever, and it does have a standlight, too.

      November 6, 2019 at 12:39 pm
      • willemjongman

        Yes I can see that getting type approval is too difficult, but for some of us it is important. Thanks for the link to the Led taillight: yours has a standlight function as well, I see, an dthat is very good. I solved the problem of the missing standlight by adding an approved Philips battery taillight to the rear rack. In fact, that light is absolutely brilliant and testimony to Philip’s century of experience with electric lighting. Unfortunately, they quickly decided that their products may well be among the best in the market, but that they were not going to make enough money, so they discontined their activity in this market, and sold the technology to Spanninga (Ellips series of taillights and their Axendo headlights).

        November 6, 2019 at 1:22 pm
        • Jan Heine

          German type approval: I remember the long and difficult process SON went through to get their Delux generator hubs approved for use with 650B and 700C wheels. They put out enough power for 20″ wheels, but modern LED lights use so little power that the light output was more than older lights had. The problem was that the law required not a certain amount of light, but a certain amount of Watts at a certain speed. In the mean time, we’d been using the old SON20 with larger wheels for many years – as long as you ride above walking speeds, it’s fine even with old halogen bulbs… The law in the U.S. is different in each state. Our state requires the light to be visible from a certain distance. It doesn’t specify whether that is in total darkness or in the environment where the bike is ridden. And WA State doesn’t require a taillight at all, just a reflector.

          For most of us, being safe is more important than complying with every detail of the law.

          November 6, 2019 at 2:49 pm
  • Rawland Rambler

    This sounds great. And “too bright” is a real issue. A cyclist went by me at dusk last evening and his rear blinking light was so bright it was blinding, and that was at dusk. It was literally a safety hazard, and of course will tick off a lot of car drivers. Of course he probably had no idea this was happening, but it’s something to be aware of.

    November 6, 2019 at 8:32 am
  • Wilfried A

    Thanks Jan for this storie about the design of my favorite taillight !!

    November 7, 2019 at 4:47 am
  • Eric Hancock

    This is a fantastic article. It reminds us that making things is difficult.

    The light really is a thing of beauty, particularly integrated into a beautiful bike like that Chapman.

    November 7, 2019 at 8:17 pm

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