When to use Intermediates or Full rain tires?

Is there a particular strategy that managers use to determine when it is best to use Intermediate or Full rain tires? I can't tell from the 2D screen, and the forecast just says rain.

Any tips?

I was thinking about asking this!

I was wondering this too when I had a rain affected race on Monday at Hungary, where it rained mid-race. After 2 laps of it starting to rain, the dry tyres were beginning to cool even on push hard. After about 4 laps on the intermediates the times began to drop off to a point where 3 laps later the times were 4 seconds slower (I did a 7 lap stint on intermediates). I then came in for the full wet tyre and fuelled to the end. I went about 4-5 seconds faster on these tyres in higher fuel than my intermediate stint. It turns out that if you study the rain guage on the weather icon, the amount of water in the guage is the amount of surface water on track. I would think that use full wets when the rain guage is near the top, intermediate tyres when it is about one quarter to maybe just over half full, and dry tyres when there is barely any or no water in the guage at all.

This is just from what I've experienced, so my recommendations may be a bit off.

I thought the gauge was a measure of humidity?

The gauge is track wetness. Generally speaking anything below 75% wetness all the way down to 0-5% wetness is inters.

Great thanks!