niznai

You're never going to get any serious ground clearance on a mini chassis because the arms are too short and very quickly you strain the driveshafts beyond the point where they can actually work.

That being said, you can get about 16mm without problems.

The best mini chassis in this situation is not a mini chassis, but the old 1/12 Porsche 959/Celica GrB chassis (which by coincidence-?! has the same wheelbase as a short mini chassis, I have the Alpine Renault body on it). The wheels are a bit larger on those cars as well, so you get another few mm. Tires with spikes help too. Downside, the chassis is very fragile. I have used strips of PCB (glassfibre reinforced plastic) to keep it together in as an inconspicuous way as I could. Lots of fun, but don't push it too hard.

Grass is a pain for anything below 1/8 scale, even for buggies like the DF03 based ones, or whatever else you want, unless clipped very short.

I prefer sawdust laid alleyways in public parks which are plentiful where I live. It is the best surface for these cars, and you can get very spectacular drifting through corners spraying sawdust everywhere, pretty much as you see on TV, in real rally stages. My avatar is one of my cars at full chat on a sawdust alley, some ten years ago. You can see the sawdust spray coming off all four whels even at top speed (car no longer accelerating). Chassis is a custom modified TA02 with shorter plates (by 2cm) made after the Tamiya FRP upgrade kit, to accomodate shorter bodyshell wheelbase.