A driver log is a record of all information pertinent to track days. If you go to the track with any sort of regular frequency, you will eventually ask yourself questions like "how many track days do I have on these brake pads", "what tire pressures did I use last time" or "what are my best lap times at this track". Your driver log should be able to answer all of these questions. Without a driver log, you will not be improving your driving or car setup as effectively as you could be, or you may run out of consumables at the most inconvenient times.
The log should have two properties:
- It should be convenient to add bits of information to it.
- It should be easy to recall existing information.
A log that is so cumbersome you never write to it while at an event is not ideal. A log that you cannot find anything in is similarly not very useful.
I used to have pocket-sized notebooks that I used for taking notes while at the track. Realistically the only things I was able to read back were tire pressure settings, tire temperature measurements, and which way the shocks were adjusted.
The notebooks were easy to write in, but impossible to find the information in.
At the same time I had a website I used for keeping track of car maintenance, parts bought, useful information found on the Internet and such. It was easy to write in when I was at home and had an Internet connection and not so easy to write in at the track when the track had no wi-fi. Browsing the website was easy at home and typically impossible at the track. This was another "write-only" solution.
Eventually I settled on a custom computerized solution that I can write to at the track (but don't, primarily due to the lack of time), and can read and search at the track. It is pretty close to the best I can do.