Ultralight Bike Lights

for UK Hill Climb racing to CTT Regulations

The problem

A few years ago, Cycling Time Trials introduced regulation 14)j):

(j) No competitor shall be permitted to start either a Type A or Type B event unless such competitor has affixed to the rear of their machine a working rear red light, either flashing or constant, that is illuminated and in a position that is clearly visible to other road users.

- all compentitors should have a rear light.

This makes a lot of sense and I fully support the stance towards fairly increasing safety (albeit with a small accessibility impact), but there's a key bit missing from the reg: an exemption for closed-road or circuit events.

As well as standard road time trials (traditionally 10, 25, 30, 50 and 100 mile, and 12 and 24hr), CTT also govern the vast majority of hill climb events. In hill climbing, weight is absolutely everything. Energy rejected to gravitational potential is so dominant over rolling restistance and air resistance that I've been able to predict my own times to within a few percent using p=mgh/t.

A typical bike light weighs between 30 and 60 grams. My relatively standard Exposure TraceR is 52g including the mount. That's worth 0.065% of my time in a hill climb. Sounds insane but over a medium-long 10-minute course that's 0.39s. That could easily be a place in the ranking.

UK Hill Climbing is famous for its' insessant and not-always-very-healthy addiction to saving grams. I can't not play my part.

The (well, my) solution

What do you really need to satisfy reg 14)j)? A red rear light that works and is visible. Assuming we want to use electric light (hmmmm), we need a light source and a power source a way to attach those in an appropriate position:

With the magic of a 3D printer, some LEDs, some CR2032 batteries, and a few design iterations...

I present to you the 6 gram bike light:

Top features include:

  • Surprisingly waterproof somehow
  • Only 6g
  • Made of PLA which some coffee shops claim is compostable but that's pushing it a bit
  • No need to remember to switch it on (because you can't)
  • Battery life tested at around 20h so you can just put the battery in when you start the warm-up for your A-race and forget about it

    • Real-world uses and testimonials

    I bravely handed hese out to teammates at Bristol South CC in the lead up to a pretty historical event; the 2021 National Hill Climb Championships at Winnat's Pass in the Peak District.

    That waterproofness I mentioned turned out to be well and truly tested on the day...

    No problems reported!

    As you can see from the results, the 45g saved might have made all the difference in earning me 151st place rather than 152nd.

    I even got a mention from GCN themselves:

    Make your own

    As usual, I've uploaded the design to Thingiverse. Find it here. It's designed to be printed with PLA with no supports required.

    You'll also need a CR2032 battery, a red 1.5v LED, and a cable tie of your choice. Enjoy!

    License: Creative commons attribution, non-commercial, no derivatives.

    E-mail me