I would run bald worn out tires on asphalt and bow ties for grass and dirt. If you run on some fluffy dirt you might want some thing more a gressive in tread pattern.
I would search for some BMX bicycle tracks to bash on. They are the best and usually if you do some exhibitions at the races while they sort the mains most tracks will let you bash there while there closed?
And I would gear conservatively in the grass and a couple of teeth higher on the pavement.
if you mixing it up gear foe the drag in the grass and watch the temps.
I like to temp about 140 when goofing in the street. Wheelie bars would be nice to.
The set up can be stiffer spring or thicker oil the traction will be higher. And the set up your running now will work at a BMX track.
GO FAST AND TRY NOT TO CRASH.................!