Dynamos and Dynamo lights

By Tristram |

This article was written way back in 2011. For a more up to date article try this.

Retro-fitting a dynamo is straightforward, but it does require rebuilding the front wheel and the hub and light are reasonably pricey, so it’s quite an initial outlay, but it will pay for itself over the years in reduced battery consumption and the ease and convenience of generating your own light.  What follows is a brief discussion of some of the dynamos, some of the lights and what is involved in a conversion.


Dynamo hubs in general have improved out of sight in the last 5 years.  The good ones generate enough power to run a very bright light with very little resistance. The charge is generated by running a series of magnets past each other.  If you have a hub on it’s own and turn the axle it feels notchy.  The notches you can feel are the magnets lining up and resisting being turned away from each other.  When the wheel is actually spinning though, this notchiness disappears.  This is because at speed, as one pair of magnets is trying to stop the wheel from turning past a spot, the next set of magnets is ready to pull the wheel towards the next spot and the two forces effectively cancel one-another out.  As a result, when the hub is not connected to a light which is turned on, it has negligible drag.  It might be too much drag for someone attempting a time trial, but not enough drag for the rest of us to even notice.  Even when the lights are on, the drag is very small, and close to unnoticeable.  They are  certainly a different beast to the old bottle dynamos which make it feel like you are riding up a hill the second they are engaged.

There are a few different options for dynamo hubs.  The two brands we carry are Shimano and Schmidt.  Both brands offer a range of models, but the variations between models within a brand are much smaller than the differences between the two brands.

Shimano dyno hubs are great value, very efficient, have high quality bearings and good seals.  The three hubs we most commonly sell are the 3n80, the Alfine and the LX.  They are pretty much identical to each other, but have different spoke counts, different provisions for disc brakes and come in either black or silver.

Schmidt hubs are similar to Shimano hubs, but are basically better in every respect and more expensive.  They have cartridge bearings, amazing seals, slightly better efficiency, weigh slightly less, and are as nicely made and finished as any hub on the market.  There are a few different models, again offering different combinations of colour, spoke count and disc compatibility.  There is also a distinction between SONdelux hubs which are lighter, lower-drag hubs with narrower flange spacing and SON hubs which are heavier, more robust hubs that generate enough power to run a halogen light at any speed.   When deciding which hub to use, the halogen issue is a bit of a non-starter, since LED lights have too many advantages over halogen to consider using a halogen light.  Furthermore, if you already own a halogen light the lower-drag hub will still run a halogen light, though it won’t output at full brightness until you are at a slightly higher speed.  The real advantages of the SON hubs are the wider flanges (which make the wheel a little stronger) and the fact that the higher energy output can help if you want to use the hub to charge devices other than lights, such as phones, GPS systems and computers.


Bike lights have also improved out of sight in recent years, thanks mainly to recent developments in LED technology.  For dyno-powered lights this means that less power is required to produce light and so lights can be bright enough to illuminate the road without making a significant difference to how hard the bike is to pedal.  LED lights are also immune to a problem which some halogen lights suffered from years ago, where the globe could overheat and pop if the speed of the bike was too high and the dynamo overpowered the light.  Modern lights also have built-in stand lights so that once the light has been run for a while there is a built up charge that keeps the light on when the bike is stopped.

There are a huge range of LED lights and we get many different ones in to order, but here are a couple we keep in stock most of the time.

The front light we keep in stock is the Busch and Muller IQ Cyo.  It is very bright and has an intelligently shaped beam of light.  The LED casts its light back onto a reflector which sends out light which illuminates the ground in front of the wheel and ahead of the rider.  The beam is cut squarely off at the top so that the light is less likely to dazzle oncoming cars/cyclists/pedestrians and so that the light is all going somewhere useful rather than just shooting off into the sky.

The rear light we stock is the Busch and Muller Toplight.  It is designed to mount nicely on a rack or fender, but we can rig it up to mount without either if needed.  It has built-in reflectors, is nice and bright, seals well and is very reliable.  It is connected to the front light and uses its stand-light so that when you are stopped at the lights people can see you.


Indicative price

Dyno systems are great value, but they aren’t cheap.  Building a replacement wheel with a dynohub, the original rim and good spokes comes in at around $300 and a pair of lights costs about the same.  But then battery lights with equivalent power are also expensive and they chew through batteries.

In the end the biggest practical advantage of dyno lights is their convenience – you don’t need to remember to replace or recharge batteries.  There’s also a lot of satisfaction to be gained not just getting to your destination under your own power, but also illuminating the way there using your own legs.


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