Heavy duty suspension?

The normal suspension of the Grand Marshal is already heavy duty, it uses suspension based on the Roamer as far as I can tell. Heavy duty suspension I think is kinda something like if you put truck suspension on a car. So more durability, can hold more weight, survives harder driving and a bit of offroading or at least driving on dirt roads. This comes at the cost of making the suspension heavier, less comfortable driving, and making it less sporty. That's the way I see it, I could be wrong about this. The standard Grand Marshal suspension mostly fits this description I think.