I double click the share button just before the race starts, this will then start the recording timer for what ever duration you have set. If notifications are on, you should get a pop up to tell you once the recording reaches its timer limit and stops. Then just double tap the share again to record the next stint.
I have mine set to 30mins, so need to record the race in two parts.
I think you can get to the settings from the share menu (single tap on share button) or if you go into the main settings menu. There are a couple of other settings you can play with depending on you PS4 model!
You can also change the button sequence of what does what (double tap/single tap/tap and hold)
If you forget to start recording when the race begins, you can capture gameplay from the last 15/30 minutes (settings dependent) if you pull up the share menu and choose to save video.
Hope that helps
Anyone run any laps yet? I would like to get an idea of laptime. Need to be on pace for final showdown
Thanks for the info mate, very helpful 👍
Haven't done any laps yet, will do over the weekend.