Very little info out there on the Fastrax tyres, aside from being targeted at bashers.
I found a link to a tyre chart on PetitRC -
http://www.petitrc.com/setup/tires/1...yTireChart.pdf
From that, Losi X-2000, especially Pink, was suggested as working on almost any hard surface;
Full list of Losi tyres available from Horizon UK