The one thing I noticed when I came over to US soil back in 1999 was how much warmer the ground temperature was, I of course came over with tyres used in the summer time of England where we had to run 25 and 30 compound to find any grip, and it was only after running on a US track that I found the 25's going to jelly after 2 minutes and the 30's in under 3 minutes.
What i had to find was the standard kit Kyosho tyres which the US guys were selling us Europeans at $35 a pair just to keep the tyres together for the 5 minute runs.
Now the opposite happened here with F1 cars, they made Rubber tyres the only tyres to use in the Tamiya series, and no one could find the grip and was simply doing doughnuts, of course it killed the interest in F1 in the UK.
Rubber may work on the hotter tracks of US soil, but they do not work on the colder tracks of Europe. We have to run Foam to get any grip.