I swapped SPRINGS to BARRELS.
It’s way more stable on bumpy soft off-road.
There’s a cons for real off-road : you loose the ability of springs to put you back to your initial direction after a wheel hit something.
YET, I got trouble with barrels 
:
I didn’t notice that at the moment. It’s front truck.
I was able to put this barrel in correct position putting all my weight at the side of the board.
I’m using the spring ajusters of the spring system, as @Trampa said it is a possibility on the old forum.
Actually, when installing the barrels, I didn’t get how the system works with the Top Bolts and the two different types of washers!? I mean the Top Bolts (M4) are thinner than the hole in the baseplate (M8). I don’t understand what the washers are supposed to do…
And this looks weird to me :
