Deciding on using a dynamo hub and lights
To Dynamo or not?
When racing ultra-endurance races, unsupported, you will find yourself riding deep into and perhaps through the night. Potentially for night after night. Thus without lights you’re not getting far at all! While lighting and power might seem like a secondary problem to solve in the kit selection game, I would however firmly place it in the priority category, with items such as: food, shelter, clothing. Simply due to the fact that without lights you will be going nowhere in dark, race over. In the same way as without food, you will be going nowhere.
Solving the issue of lighting is a two part problem. Step one is to decide if using a dynamo powered light is suitable for the event in question, and step two is to select the suitable light.
My decision making process will be different to yours, so a flow diagram might not be helpful. However, hopefully after reading the below you will have the tools to make a suitable analysis and decision yourself.
Running a SON Delux dynamo hub and Exposure REVO light for Two Volcano Sprint (road event)
1. Should you use a dynamo?
Generally I steer towards using a dynamo over not having one, most of the time. However, to decide if you should use a dynamo you need to determine if the race terrain is suitable for it to work and the race duration is sufficient to run out of battery in your battery powered lights, or other devices. Dynamos general require speeds over 10km/h to begin providing power, you can check a dynamo manufactures website. The Highland Trial 550, a proper mountain bike race in Scotland would be an example of terrain where a dynamo will be less suitable, as speeds are lower and inconsistent. Races on tarmac are generally very suitable for a dynamo and easier gravel events with longer stretches of constant speed are often suitable such as: Tour Divide, Atlas Mountain Race. There are other events such at the Silk Road Mountain Race, where there will be period a dynamo is not suitable, however given it’s remote nature and lack of charging opportunities, even with a dynamo being unsuitable at points, there will be many points where it is suitable and thus a very wise overall choice.
In order to determine if the event duration will require a dynamo, workout the number of hours you expect to be riding in the dark, by checking sunset and sunrise, misusing potential sleep hours and multiply that by the number of days you think you will be racing for, note it would be wise to add some contingency. Then compare the answer with the number of hours you battery light will run for, which it would be wise to have tested. I will often power up light with a stopwatch and check, not just go by the manufacturers guide. If the light needed is greater than available you have a few options, slow down and ride less at night. Charge your light during the day at an available service. Bring another light. Bring a battery pack. Or run a dynamo.
Running a dynamo will reduce your liability on finding somewhere to charge and potentially stopping for extended periods of time to charge. Running a dynamo will thus reduce stress and anxieties of running out of power and light. You will also be able to use the dynamo to charge other items thought a USB charger. It should be noted dynamos will cause a drag, thus slowing you down. However, this will likely be order of magnitude less that the increased stopped time to charge lights (unless you are stopping in hotels every night anyway).
One further consideration might be the amount of power you generate. As a 72kg male, I generate a reasonably amount of power, thus the drag caused and power lost by powering a dynamo is a lower percentage than that of a 45kg rider. So one solution does not fit all, and loosing 10 Watts to drag might be 10% of your generated power, rather than 5% of mine, a fair change.
Choosing a dynamo
When choosing a dynamo you do need to think about the terrain it will be mostly used on. For example SON make dynamos for road (SON Deluxe) , and off-road (SON 28). The off-road ones begin producing power at a lower speed (See graph 1 below). Therefore I have a few different dynamo wheelsets, depending on the terrain I will ride. If you can only get one dynamo, I would suggestion getting one that would be suitable for all terrains, not just select terrains.
It’s worth noting not all dynamos are built equally, both in terms of durability but also power production. Some will produce more power at lower speed, and produce a better distribution of power over a variety of speeds, or work with different lights best. Therefore, simply buying a certain brand because it is cheap, expensive or such is not advised. Considering the situation, demands and cross compatibility is. There has been extensive independent testing which you can read here:
For independent testing write up in English look here: https://www.cyclingabout.com/dynamo-hub-power-drag-testing-schmidt-son-shutter-precision-shimano/
And the original testing in Russian is here: https://skjegg.blogspot.com/2020/02/dynamo-hubs-for-your-pleasure.html
Given that dynamos add little extra weight, and their drag when not being used is negligible (SON is 1.5 Watts average) one might consider, if financially viable, running a dynamo as a default choice and supplementing with battery powered lights when wished. Doing so would built in flexibility and a backup to a bikepacking setup. As we all know, things can fail, and having multiple options for essentials is prudent.
Silk Road Mountain Race in Kyrgyzstan 2019. Running a SON 28 dynamo hub paired with an Exposure REVO and Diablo head torch.
Photo: Nadia Moro
2. Step two is to decide on the light to use.
This will depend on running dynamo or not. There is the option to use a dynamo but run battery powered lights, and simply keep a cache battery charged up from the dynamo and use this to charge your lights. However the perhaps wiser alternative, is to use a dynamo powered light, which takes it’s power directly from the dynamo. Note you cannot charge a cache battery and power lights at the same time, one or the other, as there is not enough current provided from a dynamo. For a road event I will often run a dynamo light only. However for off road events or those in more remote areas, I will run a dynamo light, and at least one battery powered light.
Selecting a dynamo light
It is worth noting that a light that is good for road, might not be good for off-road. The beam patterns desired for different terrains and speeds will very. For example K-Lite make two dynamo lights, one for on road with a longer throw (so you can see further) and one for off-road with a wider throw (so you can see around corners and to the side of trials). It’s worth investigating the main design use of the light further, for further example the Exposure Revo is mainly designed for road use. So before purchasing a light, determine what the main use will be, and find a light with a beam pattern that matches that.
Selecting a battery light
Generally if using a dynamo light, bringing a battery light as a backup or alternative is advisable. The choice of battery light will depend on your racing ambitions. If you are not riding through the night or in the dark at all, a light will only need to be a small addition, more as a backup than a main tool. However, if riding into the night a lot, or on bad terrain. Then it will be a far more serious tool. If running a battery light it is worth ensuring it can be charged from a cache battery pack as well as from the mains. Plus considering the charging time of said light, as if it does not charge fast, you might find yourself wasting time doing so.
My backup battery light is an Exposure Diablo head torch, which can be bar mounted. The benefit of a headtorch is that it can be used to fix your bike, or put up your tent in the dark – not possible with a dynamo only setup. Considering secondary requirements for lights will help you select the right tools.
Summary
Power and lights are the lifeblood of riding, and if you want to race properly, take them seriously. It’s worth pointing out that getting the brightest, most powerful and efficient lights/dynamo/charger is ideal, however other factors should be included in the decision process such as: terrain use, robustness, durability, serviceability. As it’s no good having the brightest light, if it breaks just when you need it most.
My biased opinion is that I use SON hubs, Exposure and K-lite lights. I am sure there are other great choices out there, these are just what I have used.
Graph 1: SON 28 versus Delux power output
