I have trialled and viewed a number of chairs / trikes that have mountain bike tyres as I am fed up of just using tarmac tracks.
I initially tried a trike (conventional wheelchair with mountainbike tyres and a big front wheel attached & pedals to the chair.
For me this would mean buying a new chair as the big front wheel would only fit to a non-foldable chair. As my normal chair is a foldable one it would not fit. You need the big wheel or the front castors would get stuck in the grass. This chair was operated by pedals that you steer with your hands.
I then tried a ‘mountaintrike’ which had mountainbike wheels and a big wheel at the back. I loved it. It was easy to move and steer and got me over losts of tough terrain.
They are not cheap to buy but the freedom I will get will make it worth it for me. It fits in the car with the seats down. It weighs 20kg so i need a hand to lift in / out. Google mountaintrike for videos of it. It’s cool!!
I love my bank manager!!