Kenneth
The question that I have is when would I consider a race as wet? Also would it be a bad idea to start a race with 1 mm of water on track in dry tyres? I've done a couple of races (3) in the rain but I still haven't figured out whether i should shove on inters.
Yes, its typically a bad idea to start on dry tyres with 1mm on track. But it can vary from track to track. Depending on the conditions 1mm can dry up pretty quickly.
In most cases inters will be quicker than dry tyres right down to 0.1mm, as long as they are not geting way to hot of course.
So the trick is to know if the track will stay damp long enough for you to take advantage of a stint on inters.
Wets come into use around 3.2 - 3.5, again depending on track, temps etc.