I run a T4, which is similar to the e-Firestome, on grass tracks and there are a few tyres that I have found that work well.
Firstly the fronts:
Good grass covering - Schumacher Mini Spikes (blue for wet and yellow for dry)
Dryish grass with bare soil - Proline Hole-Shots (very dry) or Proline Bowties (dry)
Rears:
Good grass covering - Schumacher Vee-2 yellow (dry), Vee-4 blue (wet)
Dryish grass with bare soil - Proline Lugnuts, Step Pins both M3 compound (dry)
or
Proline Snake Eyes, M3 compound (very dry)
All of these tyres are standard 2.2 inch 1/10th truck tyres but you will need wheels on top (make sure you drill through inside of the rim so they are not sealed. As for inserts I only use a soft foam as you get a better contact area.
Hope this helps.
