I have used and recommended dynamo setups for over a decade as I love not having to think
about charging battery lights or sourcing power for my devices.
You will often hear remarks like 'my dynamo hub doesn't slow me down at all'.
While it may not feel like it, there is always a cost when it comes to bicycle power production,
and today, I'll tell you how much a dynamo setup will likely slow you down.
Finding the exact number is surprisingly tricky.
It depends on dozens of factors including rider weight, fitness level, bike weight,
wheel size, tyre width, road surfaces, cycling speed - and the specific hub, charger and lights that are fitted to your bike.
To get a sense of the drag, I will be creating two different rider scenarios and simulating them on both flat and 5% road gradients.
We will then calculate the speed differences of both the highest and lowest-drag hubs when paired
with a USB charger and dynamo lights.
Let's start with a quick overview of the dynamo components.
Hub dynamos generate power by passing magnets over a copper coil, and it is here where the physical drag occurs.
Hubs actually vary a surprising amount in terms of both efficiency and power output,
you'll be able to see the lowest-drag hubs on some graphs shortly.
USB chargers convert the power from your hub into a useable form at the USB plug.
Depending on how the electronics have been designed, there are power output and efficiency differences here too.
But importantly, the resistance at the wheel is based on how much power your plugged-in device is drawing from the hub,
and this can vary quite a bit.
For example, a Garmin GPS at 25KPH would likely have 6 or 7x less resistance than a big smartphone.
When it comes to lighting, brighter lights will typically slow you down more than dimmer lights.
Most dynamo lights achieve their maximum brightness, and therefore drag, between 15 and 20KPH.
For today's estimations, we will look at two different rider scenarios.
The smaller rider weighs 60kg and their bike plus gear is 25kg.
As the average cyclist pedals at around two watts-per-kilogram on a long ride, this rider will be pushing 120-watts for the simulation.
The bigger rider is 90kg and their bike plus gear is also 25kg. They will pedal their bike at 180-watts.
I am using dynamo power and drag data collected on Skjegg Blogspot.
You can find links to the original test and my interpretation of the results in the video description.
I have then used Bike Calculator to determine the speed differences at different power outputs.
Through my own real-world testing, I have found this tool to work with very high accuracy.
Let's start with the hub drag with nothing connected.
This graph shows the drag of four different dynamo hubs at speeds between 5 and 30KPH.
You will notice that most hubs increase in resistance the faster you go; the exception is the Schmidt SON
which has some black magic going on to achieve a somewhat steady drag at different riding speeds.
The smaller rider on a flat road is between 14 seconds and 54 seconds slower per hour.
This drops to between 7 and 43 seconds under our bigger rider.
The smaller rider will be 29 to 43 seconds slower on a climb, while the bigger rider will be 22 to 32 seconds behind.
Essentially, with nothing connected, dynamo hub drag will be imperceivable to a rider.
Now let’s look at how much a very bright 100lux dynamo light will slow you down.
I have selected the data from the B&M IQ-X, which is one of the brightest options available and one that I personally recommend.
On the flat, a smaller rider with a dynamo light is 2:38 to 3:36 behind per hour depending on the hub.
A bigger cyclist is less affected by drag with a time penalty of 1:48 to 2:24 per hour.
The Shimano UR700 hub has pretty substantial time losses on the climb - it's 3:22 to 3:47 behind per hour.
The SON28 has approximately half the drag, so the time losses are 1:41 to 1:52 per hour,
although it is also offering approximately 20% less light at those speeds.
We will be using a kLite USB charger for this example, and we will be assuming that your device is consuming
all power available at the USB plug.
As the Shimano UR700 provides 25% more power at the USB plug than the SON hub, this is not a perfectly fair comparison.
But alas, when a charger is providing good power on a flat road, it will slow a smaller rider between 1:30 and 2:53 per hour,
and a bigger rider between 1:12 and 2:20 per hour.
On the climb, I cannot simulate the SON as it's not yet making good power with the kLite charger,
so we will compare the two Shimano hubs instead.
The smaller cyclist will be between 4 seconds and 2:24 behind per hour, and the bigger cyclist will be 11 seconds to 1:48 behind.
I personally use a Cinq Plug5 Plus USB charger and Schmidt SON hub dynamo on my bike,
so I'm running these predictions more for my own curiosity than anything else.
Using the Schmidt hub charging efficiencies from the kLite graph and the power output figures of the Plug5 Plus
from some other independent testing, I can crunch the numbers to try to predict what my more powerful USB charger will
likely cost our two simulated riders.
On the flat, the smaller cyclist will be 2:13 behind per hour while the bigger cyclist will be 1:34 behind.
On the climb, the smaller cyclist will be 1:34 behind while the bigger cyclist will be just 1:08 behind.
Ok, to summarise, hub dynamos very run well with nothing connected.
On the flat, my Schmidt hub is probably slowing me down only 7-seconds per hour.
When charging a smartphone, I am likely losing around 1.5 minutes per hour, which I think is very reasonable
given how convenient it is to always have power on tap.
A low-power device like a Garmin GPS would likely cost me around 20 seconds per hour in comparison.
That said, dynamo lights are my number one reason to use a dynamo setup,
and I'm happy to lose a couple of minutes per hour at night for the sheer convenience.
But, if I was ultra racing at the pointy end of the field, this data would make me consider
whether I can get by with battery-powered lights, as I could potentially save 25-40 minutes in an overnight push
- which is a decent nap!
When an ultra course allows for it, less bright dynamo lights could be a better option.
The B&M Cyo, which is half the brightness of the IQX, would probably cost around a minute per hour with a SON hub.
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I'll catch you next video.