Interesting info about these tires from the Kyosho Mini-Z/dnano development blog:
http://ameblo.jp/kyoshoblog-en/page-11.html#main
Excerpt from blog (note in a previous entry the guy says that these tires are expensive since they're all made by hand !
The suitable surface is of cource the dNaNo home circuit, but these sponge tires also show better grip than rubber tires on smooth concrete floors and wooden floors!!
However, the sponge tires are not very good on dusty surfacs, so before running clean the floor with a damp cloth.
These tires also show good grip on carpets but the tire wear might be fast because of the high grip.
Lastly, on urethane tracks, the car overturns due to the super high grip. So I recommend rubber tires.
ＤＮＴ004-20 Sponge tire(FA/FRA/20°/2pcs)
This tire fits FA and FRA size wheels.
This 20-deg type is good for FRA rear wheels.
ＤＮＴ004-30 Sponge tire(FA/FRA/30°/2pcs)
This tire also goes with FA and FRA size wheels.
This 30-deg type is good for front wheels.
ＤＮＴ005-20 Sponge tire(RA/20°/2pcs)
This tire is for RA size wheels.
Good for rear.