Sorry guys - not interested in foams on Off-road cars - next thing we'll be mounting 200mm TC shells on them again...
Rubber road tyres, maybe. Something cheap, very hard wearing and relatively low grip.
I've mentioned these before, but the Proline Dirt Hawgs are popular in one or two clubs as a control tyre, and can be made to provide some grip. They last years, and mount on 2.2 rims. Something like
this.
They're also carpet-kind...