The 12 hour Time Trial

By Richard Bideau

Yorkshire district together with cycling team Vive Le Velo are promoting a new 12 hour event in 2023. A lot of work is being done to widen the appeal of what has become something of a niche event. I’m told that there are already a good number of entries, particulary from triathletes. To help raise awareness of this rather special type of time trial I’ll share some of my own experiences on this post.

CTT entries for the event are here.

There is also a facebook page with up-to-date information on the course.

Format of a 12 hour time trial

Sometimes known as the half-day event, the 12 hour differs from the fixed standard distances in that instead of being a specified distance, the time trial is for a fixed duration. The beginning is the same as for any time trial with riders setting off at one minute intervals from a specified start location. The finish is a little different. A ‘finishing circuit’ is used during the final hours. This is a section of road of no less than 10 miles in length that is covered repeatedly. Instead of having a single finish timekeeper, there are many, distributed around the circuit and typically around 2 miles apart. When 12 hours have elapsed, the rider continues at race speed until the next timekeeper is passed. The times at which the rider passed this timekeeper and the preceeding one are used to generate the result. As the distance to each of these two timekeepers is known from the course measurement and the number of laps of the finishing circuit completed, the distance that the rider completed in exactly 12 hours is estimated by linear interpolation. Between the start and the finishing circuit events typically use a number of different circuits, the riders being directed by marshals as to when to move to the next circuit.

Regulations regarding 12 hour courses are covered by CTT regulation number 35.


Good pacing is essential for sucess in all types of time trial. For the 12 hour it is especially difficult to get right because few riders have much experience of efforts of that duration. My own experience is consistent with other riders that I have spoken with – a 12 hour is ridden in zone 2, ‘endurance’ level.

For each of the 12s I have ridden, I have targeted a power of 70% FTP and that has seemed about right. This power level feels extremely easy in the first few hours – certainly the first 100 miles seems almost like cheating when compared to a 100 mile event. However, the same power in the final hours on the finishing circuit feels extremely hard to sustain.


When planning my first 12 hour, I did some basic energy calculations to help me understand how much I needed to eat.

The figures are rather daunting: at my target power the energy I was to push through the cranks would exceed 10000 kJ. In round numbers this meant I would burn around 10000kcal (it just so happens that the typical energy conversion efficiency of a trained athlete is the same as the 0.238 conversion factor between calories and Joules).

10000 kcal! That is a lot of food! Too much in fact. During excercise the maximum amount of ingested carbohydrate that the body can process is typically around 90g per hour, equivalent to approximately 340kcal per hour, or around 4000kcal over 12 hours. That leaves a big deficit. It is likely to be even worse as the 90g per hour fails to take into account the many factors that affect ability to eat after hours of riding. My own experince is that eating in the final hours is out of the question.

Clearly, a lot of energy has to come from stored fat. Nonetheless, it is essential to make as much use of additional food as possible.

To be continued…