Is there a setting that I can change to stop the software automatically requesting a pitstop for me during a race? Thanks.
Hmm... did you not see Dave's answer? The auto pit request is based on your scheduled stop. If you change that schedule (or have none scheduled at all) you won't get an auto request.
That's not true. I have had lots of times when I had a stop scheduled and the auto pit request came up off schedule. I've also had lots of times when I had already stopped, I had plenty of fuel there's no other scheduled stop and the game auto-requests toward the end of the race. Also it's come up when I had no pit stop scheduled at all. It may be linked to what the game calculates your fuel usage to be and when the game gets too helpful and requests a pit stop for you so you don't run out of gas.... except the game is often wrong.