Hi
I started a thread here to discuss all makes of foam tyres. The result was pretty mixed as some tyres perform on some tracks but not on others.
Mainly you have 2 typres of tyres. GRP rubber and JAP rubber. Ellegi, Power, Jaco and Fast along with a lot of others use GRP where Sato Seiki, Mono tuning (Rebadged sato Seiki) GQ and Speedming use JAP rubber (I'm sure this is not its technical name!)
GRP USUALLY! have high grip with high wear and also a tendancy to chunk at the edges where JAP have just as much grip on certain tracks and lower wear rate with less chunking.
Most tyres, GRP or JAP are made up of 3 rings of different compounds glued together to make the complete tyre. Yokomo (i think!) make a tyre where the rings are glued on top of each other and not next to each other and these are more expensive but i have heard very low wear and high grip.
In the end its what works on your track. I almost always use GQ 37s all round when out track is warm and dry. 40's in a longer final.
Cheers